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Unsolved Problems

Strings

Printing

Retrieve a string containing ampersands from the variables in a url

My PHP script first does a query to obtain customer info for a form. The form has first name and last name fields among others. The customer has put entries such as "Ron & Jean" in the first name field in the database. Then the edit form script is called with variables such as

"http://myserver.com/custinfo/edit.php?mode=view&fname=Ron & Jean&lname=Smith".

The script variable for first name $_REQUEST['firstname'] never gets beyond the "Ron" value because of the ampersand in the data.

I have tried various functions like urldecode but all to no avail. I even tried encoding the url before the view screen is painted so that the url looks like "http://myserver/custinfo/edit.php?mode=view&fname="Ronxxnbsp;xxamp;xxnbsp;Jean"&lname=SMITH". (sorry I had to add the xx to replace the ampersand or it didn't display meaningful url contents the browser sees.)

Of course this fails for the same reasons. What is a better approach?

java

Map<String, String> params = new HashMap<String, String>();
params.put("mode", "view");
params.put("fname", "Ron & Jean");
params.put("lname", "Smith");

StringBuilder buffer = new StringBuilder();
for (Map.Entry<String, String> entry : params.entrySet()) {
buffer.append(URLEncoder.encode(entry.getKey(), "UTF-8"))
.append("=")
.append(URLEncoder.encode(entry.getValue(), "UTF-8"));
}
System.out.println(buffer.toString());

groovy

// Given the nature of the question text, I am assuming the question
// is how to produce a application/x-www-form-urlencoded compliant string

def basename = 'http://somedomain.com/somebase/'
def parameter = 'Bart & Lisa'
// equivalent to php
println basename + URLEncoder.encode(parameter)
// recommended approach is to specify encoding
println basename + URLEncoder.encode(parameter, "UTF-8")

scala

import java.net.URLEncoder

val params = Map("mode"->"view", "fname"->"Ron & Jean", "lname"->"Smith")
var url = ""

for ((k, v) <- params) { url += URLEncoder.encode(k) + "=" + URLEncoder.encode(v) }

println(url)

import java.net.URLEncoder
val params = Map("mode"->"view", "fname"->"Ron & Jean", "lname"->"Smith")
(for ((k, v) <- params) yield URLEncoder.encode(k) + "=" + URLEncoder.encode(v) ).mkString("&")

python

# I'm not really sure this is what the site is for,
# but the one unsolved problem for python was grating me.
# Anyway, I think this is what you're looking for.

from urllib import urlencode

query_dict = {'mode': 'view',
'fname': 'Ron & Jean',
'lname': 'Smith'}

print urlencode(query_dict.items())

# Which will be 'lname=Smith&mode=view&fname=Ron+%26+Jean'.

fsharp

//the problem arises due to the fact that you've attempted to apply HTML entities encoding rather than URL encoding to your data!
//in F#, for example, assuming you would call this function with fname and lname parameters, this would produce the desired output
let getProperUrl fname lname = sprintf "http://myserver.com/custinfo/edit.php?mode=view&fname=%s&lname=%s" (HttpUtility.UrlEncode fname) (HttpUtility.UrlEncode lname)

php

/************************
* This is definitely not what this site is about
* This is not a site where you can get help with various problems
* It's a site where you can say:
* "How do you do the following in your language"
*
*************
*
* Anyway...
* I would use urlencode like you have tried
* (or to be on the safe side: rawurlencode() )
************************/

$parameter = "Bart & Lisa";
echo "<a href='".basename(__FILE__)."?fname=".$parameter."'>?fname=".$parameter."</a><br />\n";
echo "<a href='".basename(__FILE__)."?fname=".rawurlencode($parameter)."'>?fname=".rawurlencode($parameter)."</a><br />\n";

echo "<pre>", print_r($_REQUEST, true), "</pre>";

/***************
* Try to save this as a file and run the script
************
* If you hover the mouse over the link, they will look exactly the same
* but if you click them, they will output differently
***************/

// Cheers, "Josso"

echo("The given input URL is mal-formed; it should be URL-encoded. Use urldecode() on each argument to decode it.");

Declaration

Define a multiline string

Define the string:

"This

Is

A

Multiline

String"

ruby

text = <<"HERE"
This
Is
A
Multiline
String
HERE

text = "This\nIs\nA\nMultiline\nString"

java

String text = "This\nIs\nA\nMultiline\nString";

String text =
"This\n" +
"Is\n" +
"A\n" +
"Multiline\n" +
"String"

perl

$text = 'This
Is
A
Multiline
String';

$text = <<EOF;
This
Is
A
Multiline
String
EOF

groovy

def text =
"""This
Is
A
Multiline
String"""

def text = "This\nIs\nA\nMultiline\nString"

scala

val text = """This
Is
A
Multiline
String"""

val text = "This\nIs\nA\nMultiline\nString"

python

text = """This
Is
A
Multiline
String"""

# with proper indentation
text = (
"This\n"
"Is\n"
"A\n"
"Multiline\n"
"String"
)

cpp

std::string text =
"This\n"
"Is\n"
"A\n"
"Multiline\n"
"String";

String^ text = L"This\nIs\nA\nMultiline\nString";

std::string text = "This\nIs\nA\nMultiline\nString";

fsharp

let multiline = "This\nIs\nA\nMultiline\nString"

let multiline = "This
Is
A
Multiline
String"

erlang

Text = "This\nIs\nA\nMultiline\nString",

ocaml

"This\nIs\nA\nMultiline\nString"

"This
Is
A
Multiline
String"

csharp

string output = "This\nIs\nA\nMultiline\nString";

string output = @"This
Is
A
Multiline
String";

php

$multiline = <<<ML
This
Is
A
Multiline
String
ML;

$multiline = "This
Is
A
Multiline
String";

$multiline = "This\nIs\nA\nMultiline\nString";

clojure

(def multiline "This\nIs\nA\nMultiline\nString")

Manipulation

Text wrapping

Wrap the string "The quick brown fox jumps over the lazy dog. " repeated ten times to a max width of 78 chars, starting each line with "> ", yielding this result:

> The quick brown fox jumps over the lazy dog. The quick brown fox jumps
> over the lazy dog. The quick brown fox jumps over the lazy dog. The
> quick brown fox jumps over the lazy dog. The quick brown fox jumps
> over the lazy dog. The quick brown fox jumps over the lazy dog. The
> quick brown fox jumps over the lazy dog. The quick brown fox jumps
> over the lazy dog. The quick brown fox jumps over the lazy dog. The
> quick brown fox jumps over the lazy dog.

ruby

prefix = "> "
string = "The quick brown fox jumps over the lazy dog. " * 10
width = 78
realwidth = width - prefix.length
print string.gsub(/(.{1,#{realwidth}})(?: +|$)\n?|(.{#{realwidth}})/, "#{prefix}\\1\\2\n")

java

String prefix = "> "; String input = "The quick brown fox jumps over the lazy dog.";

String[] lines = WordUtils.wrap(StringUtils.repeat(input, 10), 72 - prefix.length()).split("\n");

for (String line : lines) System.out.printf("%s%s\n", prefix, line);

perl

use Text::Wrap;
$text = "The quick brown fox jumps over the lazy dog. ";
$Text::Wrap::columns = 73;
print wrap('> ', '> ', $text x 10);

$_ = "The quick brown fox jumps over the lazy dog. " x 10;
s/(.{0,70}) /> $1\n/g;
print;

groovy

// no built-in fill, define one using brute force approach
def fill(text, width=80, prefix='') {
width = width - prefix.size()
def out = []
List words = text.replaceAll("\n", " ").split(" ")
while (words) {
def line = ''
while (words) {
if (line.size() + words[0].size() + 1 > width) break
if (line) line += ' '
line += words[0]
words = words.tail()
}
out += prefix + line
}
out.join("\n")
}
println fill('The quick brown fox jumps over the lazy dog. ' * 10, 72, '> ')

// no built-in fill, define one using lastIndexOf
def fill(text, width=80, prefix='') {
def out = ''
def remaining = text.replaceAll("\n", " ")
while (remaining) {
def next = prefix + remaining
def found = next.lastIndexOf(' ', width)
if (found == -1) remaining = ''
else {
remaining = next.substring(found + 1)
next = next[0..found]
}
out += next + '\n'
}
out
}
println fill('The quick brown fox jumps over the lazy dog. ' * 10, 72, '> ')

prefix = '> '
input = 'The quick brown fox jumps over the lazy dog. '
wrap(input * 10, 72 - prefix.size()).eachLine{ println prefix + it }

scala

val prefix = "> " ; val input = "The quick brown fox jumps over the lazy dog."

WordUtils.wrap(input * 10, 72 - prefix.length).split("\n") foreach {(x) => printf("%s%s\n", prefix, x)}

python

import textwrap
print textwrap.fill("The quick brown fox jumps over the lazy dog. " * 10,
72, initial_indent="> ", subsequent_indent="> ")

cpp

String^ input = ::copies("The quick brown fox jumps over the lazy dog. ", 10);
String^ sep = " "; String^ prefix = "> ";

String^ wrapped = textwrap(input, 74 - prefix->Length, sep, prefix);
Console::WriteLine("{0}", wrapped);

fsharp

let prefix = "> "
let input = "The quick brown fox jumps over the lazy dog. "

(String.split ['\n'] (textwrap (copies input 10) (73 - prefix.Length))) |> List.iter (fun line -> printfn "%s%s" prefix line)

erlang

TextWrap = textwrap(string:copies(Input, 10), 73 - length(Prefix)),
lists:foreach(fun (Line) -> io:format("~s~n", [string:concat(Prefix, Line)]) end, string:tokens(TextWrap, "\n")).

ocaml

(* ocamlbuild -no-hygiene textwrap.native && ./textwrap.native *)

let wrap s prefix width =
let width = width - (String.length prefix) in
let len = String.length s in
let rec loop start =
if start >= len then
[]
else
let stop = min (len - start) width in
let sub = String.sub s start stop in
(prefix ^ sub) :: loop (start+stop)
in
loop 0
in

let wrap_and_print s prefix width =
List.iter print_endline (wrap s prefix width)
in
let s = ref "" in
for i = 1 to 10 do
s := !s ^ "The quick brown fox jumps over the lazy dog. "
done;
wrap_and_print !s "> " 78

csharp

using System;
using System.Text;
using System.Linq; // used for Array.ToList() extension

public class TextWrapper {

/// <summary>
/// Wrap the given text to a given width.
/// </summary>
/// <param name="text">The text to be wrapped</param>
/// <param name="width">The maximum width of each line</param>
/// <param name="prefix">Begin each line with this prefix</param>
/// <returns>The wrapped text</returns>
public string Wrap(string text, int width, string prefix) {

var words = text.Split(' ').ToList();
var result = new StringBuilder(prefix);

width = width - prefix.Length;
prefix = "\n" + prefix;

int lineSize = 0;
foreach (var word in words) {
int wordLen = word.Length;

// Do we need to start a new line?
if ((lineSize + wordLen) > width) {
result.Remove(result.Length - 1, 1); // remove trailing space
lineSize = 0;
result.Append( prefix );
}

result.Append(word).Append(' ');
lineSize += wordLen + 1;
}

return result.ToString();
}

public static void Main() {
var prefix = "> ";
var sentence = "The quick brown fox jumps over the lazy dog. ";

var text = "";
for (int i = 0; i < 10; i++)
text += sentence;

// The description said lines of length 78, but
// the example was 72...
Console.WriteLine(new TextWrapper().Wrap(text, 72, prefix));
}
}

php

$s = str_repeat("The quick brown fox jumps over the lazy dog. ", 10);
$s = wordwrap($s, 76, "WRAP");
$s = explode("WRAP", $s);
foreach ($s as $part) {
$res .= "> " . $part . "\n";
}
echo $res;

echo '> '.wordwrap(str_repeat('The quick brown fox jumps over the lazy dog. ', 10), 70,"\n> ")."\n";

clojure

(doseq [line (re-seq #".{0,70} "
(repeat "The quick brown fox jumps over the lazy dog. " 10))] (println ">" line))

Remove leading and trailing whitespace from a string

Given the string " hello " return the string "hello".

ruby

puts " hello ".strip

" hello ".strip!

java

String s = " hello "; String trimmed = s.trim();

perl

my $string = " hello ";
$string =~ s{
\A\s* # Any number of spaces at the start of the string
(.+?) # Remember any number of characters until we reach
\s*\z # any number of spaces at the end of the string
}{
$1 # Leave the characters we remembered
}x;

my $string = " hello ";
$string =~ s{\A\s*}{};
$string =~ s{\s*\z}{};

#Modification History:
# 2009-MAR-17: GGARIEPY: [creation] (geoff.gariepy@gmail.com)

$string = " hello ";
$string =~ s/^\s+|\s+$//g; # All the action happens in one regex!

# Regex Notes:
# ^ - anchors to the beginning of the string
# $ - anchors to the end of the string
# g - causes regex to match as many times as possible
# | - logical OR

groovy

assert "hello" == " hello ".trim()

scala

val s = " hello " ; val trimmed = s.trim

python

assert 'hello' == ' hello '.strip()

cpp

String^ s = " hello "; String^ trimmed = s->Trim();

fsharp

let s = " hello "
let trimmed = s.Trim()

let trimmed = " hello ".Trim()

erlang

Trimmed = string:strip(S),

csharp

string str = " hello ";
str = str.Trim();
Console.WriteLine(str);

php

$hello_trimmed = trim(" hello ");

haskell

unwords (words " hello ")

clojure

(use 'clojure.contrib.str-utils2)
(trim " hello ")

Simple substitution cipher

Take a string and return the ROT13 and ROT47 (Check Wikipedia) version of the string.
For example:
String is: Hello World #123
ROT13 returns: Uryyb Jbeyq #123
ROT47 returns: w6==@ (@C=5 R`ab

ruby

rot13 = "Hello World #123".tr!("A-Za-z", "N-ZA-Mn-za-m")
rot47 = "Hello World #123".tr!("\x21-\x7e", "\x50-\x7e\x21-\x4f")

java

CharArrayWriter rot13 = new CharArrayWriter() ;
for (char c : i ) {
char lc = Character.toLowerCase(c) ;
rot13.append( c += ( (lc >= 'a' && lc <= 'm') ? 13 : ( (lc >= 'n' && lc <= 'z') ? -13 : 0 ) )) ;
}

CharArrayWriter rot47 = new CharArrayWriter() ;
for (char c : i )
rot47.append( c += ( (c >= '!' && c <= 'O') ? 47 : ( (c >= 'P' && c <= '~') ? -47 : 0 ) )) ;

perl

sub rot13 {
my $str = shift;
$str =~ tr/A-Za-z/N-ZA-Mn-za-m/;
return $str;
}

sub rot47 {
my $str = shift;
$str =~ tr/!-~/P-~!-O/;
return $str;
}

my $string = 'Hello World #123';

print "$string\n";
print rot13($string)."\n";
print rot47($string)."\n";

groovy

char rot13(s) {
char c = s
switch(c) {
case 'A'..'M': case 'a'..'m': return c+13
case 'N'..'Z': case 'n'..'z': return c-13
default : return c
}
}
String.metaClass.rot13 = {
delegate.collect(this.&rot13).join()
}

from = '!"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~'
to = 'PQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~!"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNO'
String.metaClass.rot47 = {
delegate.collect{ int found = from.indexOf(it); found < 0 ? it : to[found] }.join()
}

assert 'Hello World #123'.rot13() == 'Uryyb Jbeyq #123'
assert 'Hello World #123'.rot47() == 'w6==@ (@C=5 R`ab'

scala

val uppers = 'A' to 'Z'
val lowers = 'a' to 'z'

val alpha13 = (uppers ++ lowers).mkString
val beta13 = ((uppers drop 13) ++ (uppers take 13) ++ (lowers drop 13) ++ (lowers take 13)).mkString

val alpha47 = """!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~"""
val beta47 = """PQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNO"""

// generic translation function
def rot (alpha: String, beta: String)(c: Char) = if (alpha contains c) beta(alpha indexOf c) else c

// specific translation functions curried with the respective alphabets
val rot13 = rot(alpha13, beta13) _
val rot47 = rot(alpha47, beta47) _

assert(("Hello World #123" map rot13).toString == "Uryyb Jbeyq #123")
assert(("Hello World #123" map rot47).toString == "w6==@ (@C=5 R`ab")

python

# rot13, readable
rot13_tbl = string.maketrans("ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz", "NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm")
string.translate("Hello World #123", rot13_tbl)

#
# "a bad programmer can write bad code in any language"
#

# rot13, "clever"
string.translate("Hello World #123", string.maketrans(string.lowercase+string.uppercase, string.lowercase[13:]+string.lowercase[:13]+string.uppercase[13:]+string.uppercase[:13]))

# rot47, very "clever"
''.join([ord(c) in range(33,127) and chr(((ord(c)-33+47)%(127-33))+33) or c for c in "Hello World #123"])

"Hello World #123".encode('rot13')

cpp

#include <algorithm>
#include <iostream>
#include <cctype>
using namespace std;

int rot13(int c) {
if (!isalpha(c)) {
return c;
} else {
char start = islower(c) ? 'a' : 'A';
return ((c - start) + 13) % 26 + start;
}
}

int rot47(int c) {
if (c < 33 || c > 126) {
return c;
} else {
return ((c - 33) + 47) % 94 + 33;
}
}

int main(int argc, char **argv) {
for (int i = 0; i < argc; ++i) {
string original = argv[i];

string rot13enc = original;
transform(original.begin(), original.end(), rot13enc.begin(), rot13);

string rot47enc = original;
transform(original.begin(), original.end(), rot47enc.begin(), rot47);

cout << "original: " << original << endl
<< "rot 13: " << rot13enc << endl
<< "rot 47: " << rot47enc << endl;
}
return 0;
}

erlang

rot13(Str) ->
lists:map(fun(A) ->
if
A >= $A, A =< $Z -> ((A - $A + 13) rem 26) + $A;
A >= $a, A =< $z -> ((A - $a + 13) rem 26) + $a;
true -> A
end
end, Str).

rot47(Str) ->
lists:map(fun(A) ->
if
A >= $!, A =< $~ ->
((A - $! + 47) rem 94) + $!;
true -> A
end
end, Str).

php

Case

Make a string lowercase

Transform "Caps ARE overRated" into "caps are overrated"

ruby

"Caps ARE overRated".downcase

java

"Caps ARE overRated".toLowerCase();

perl

print lc "Caps ARE overRated"

groovy

println "Caps ARE overRated".toLowerCase()

scala

"Caps ARE overRated".toLowerCase

python

"Caps ARE overRated".lower()

cpp

std::string s = "Caps ARE overRated";
std::string sl(boost::to_lower_copy(s));

String(L"Caps ARE overRated").ToLower();

fsharp

printfn "%s" ("Caps ARE overRated".ToLower())

printfn "%s" (String.lowercase "Caps ARE overRated")

erlang

io:format("~s~n", [string:to_lower("Caps ARE overRated")]).

ocaml

String.lowercase "Caps ARE overRated";;

csharp

string str = "Caps ARE overRated";
str = str.ToLower() ;
Console.WriteLine(str);

php

echo strtolower("Caps ARE overRated");

clojure

(.toLowerCase "Caps ARE overRated")

Capitalise the first letter of each word

Transform "man OF stEEL" into "Man Of Steel"

ruby

caps = text.gsub(/\w+/) { $&.capitalize }

caps = text.split.each{|i| i.capitalize!}.join(' ')

java

String input = "man OF stEEL";
StringTokenizer tokenizer = new StringTokenizer(input);
StringBuffer sb = new StringBuffer();
while (tokenizer.hasMoreTokens()) {
String word = tokenizer.nextToken();
sb.append(word.substring(0, 1).toUpperCase());
sb.append(word.substring(1).toLowerCase());
sb.append(' ');
}
String text = sb.toString();

StringBuilder sb = new StringBuilder("man OF stEEL"); String s = sb.toString();
int last = s.length() - 1;

for (int i = 0; i <= last; ++i)
if (Character.isSpaceChar(s.charAt(i)) && i < last) { ++i; sb.setCharAt(i, Character.toUpperCase(s.charAt(i))); }
else if (i == 0) sb.setCharAt(i, Character.toUpperCase(s.charAt(i)));
else sb.setCharAt(i, Character.toLowerCase(s.charAt(i)));

Matcher m = Pattern.compile("(\\w+)").matcher("man OF stEEL"); StringBuffer sb = new StringBuffer(32), rsb = new StringBuffer(8);

while (m.find())
{
rsb.replace(0, rsb.length(), m.group().toLowerCase()); rsb.setCharAt(0, Character.toUpperCase(rsb.charAt(0)));
m.appendReplacement(sb, rsb.toString());
}
m.appendTail(sb);

String text = WordUtils.capitalizeFully("man OF stEEL");

perl

$text =~ s/(\w+)/\u\L$1/g;

groovy

def capitalize(s) { s[0].toUpperCase() + s[1..-1].toLowerCase() }
caps = "man OF stEEL".replaceAll(/\w+/) { w -> capitalize(w) }

caps = "man OF stEEL".replaceAll(/\w+/) { w -> StringUtils.capitalize(w.toLowerCase()) }

caps = WordUtils.capitalizeFully("man OF stEEL")

scala

def capitalize(s : String) = { s(0).toUpperCase + s.substring(1, s.length).toLowerCase }

"man OF stEEL".split("\\s") foreach {(x) => text.append(capitalize(x)).append(" ")}

val text = WordUtils.capitalizeFully("man OF stEEL")

val text = StringUtils.join("man OF stEEL".split("\\s") map {(x) => StringUtils.capitalize(x.toLowerCase) + " "})

// can be solved without external libraries
(("man OF stEEL" toLowerCase) split " " map (_ capitalize)).mkString(" ")

python

from string import capwords
capwords("man OF stEEL")

' '.join(s.capitalize() for s in "man OF stEEL".split())

cpp

std::string words = "mAn OF stEEL";
std::transform(words.begin(), words.end(), words.begin(), ToCaps<>());

StringBuilder^ sb = gcnew StringBuilder(L"man OF stEEL");

for (int i = 0, isFirst = 1; i < sb->Length; ++i)
{
sb[i] = Char::IsWhiteSpace(sb[i]) ? (isFirst = 1, sb[i]) : isFirst ? (isFirst = 0, Char::ToUpper(sb[i])) : Char::ToLower(sb[i]);
}

std::string words = "mAn OF stEEL";
std::vector<std::string> swv;

boost::split(swv, words, boost::is_any_of(" "));
std::string newwords = (std::for_each(swv.begin(), swv.end(), StringTAndJ(WordToCaps))).value();

fsharp

let words = String.Join(" ", Array.map (fun (s : String) -> (String.capitalize (s.ToLower()))) ("man OF stEEL".Split [|' '|]))

let wordlst = List.map (fun s -> (String.capitalize (String.lowercase s))) (String.split [' '] "man OF stEEL")
let words = new StringBuilder(List.hd wordlst)
for (s : String) in (List.tl wordlst) do (words.Append(" ").Append(s))

erlang

Caps = string:join(lists:map(fun(S) -> to_caps(S) end, string:tokens("man OF stEEL", " ")), " "),

csharp

System.Threading.Thread.CurrentThread.CurrentCulture.TextInfo.ToTitleCase("man OF stEEL".ToLowerInvariant());

php

echo ucwords(strtolower("man OF stEEL"));

clojure

(use 'clojure.contrib.str-utils2)
(join " " (map capitalize (split "man OF stEEL" #" ")))

Numbers

Mathematical

Find the distance between two points

ruby

distance = Math.sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1))

java

double distance = Point2D.distance(x1, y1, x2, y2);

Point2D point1 = new Point2D.Double(x1, y1);
Point2D point2 = new Point2D.Double(x2, y2);
double distance = point1.distance(point2);

perl

use Math::Complex;
$a = Math::Complex->make(0, 3);
$b = Math::Complex->make(4, 0);
$distance = abs($a - $b);

groovy

distance = distance(x1, y1, x2, y2)

distance = sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1))

scala

val distance$ = distance((34, 78), (67, -45))
println(distance$)

val distance$ = distance(new Point(34, 78), new Point(67, -45))
println(distance$)

def distance (p1: (Int, Int), p2: (Int, Int)) = {
val (p1x, p1y) = p1
val (p2x, p2y) = p2
val dx = p1x - p2x
val dy = p1y - p2y
Math.sqrt(dx*dx + dy*dy)
}
println(distance((34, 78), (67, -45)))

python

# problem description doesn't say 2D points ;)
from math import sqrt
print sqrt(sum((x-y)**2 for x,y in zip(a, b)))

cpp

Point p1 = {34, 78}, p2 = {67, -45};
double distance = ::distance(p1, p2);
Console::WriteLine("{0,3:F2}", distance);

fsharp

let distance' = distance (34, 78) (67, -45)
printfn "%3.2f" distance'

erlang

Distance = distance({point, 34, 78}, {point, 67, -45}),
io:format("~.2f~n", [Distance]).

Distance = distance(point:new(34, 78), point:new(67, -45)),
io:format("~.2f~n", [Distance]).

ocaml

type point = { x:float; y:float };;
let distance a b = sqrt((a.x -. b.x)**2. +. (a.y -. b.y)**2.);;

csharp

System.Drawing.Point p = new System.Drawing.Point(13, 14),
p1 = new System.Drawing.Point(10, 10);
double distance = Math.Sqrt(Math.Pow(p1.X - p.X, 2) + Math.Pow(p1.Y - p.Y, 2)));

php

$distance = sqrt( pow(($x2 - $x1), 2) + pow(($y2 - $y1),2) );

class Point2D {
var $x;
var $y;
function __construct($x, $y) {
$this->x = $x;
$this->y = $y;
}
}
$a = new Point2D($x1,$y1);
$b = new Point2D($x2,$y2);
$distance = sqrt( pow(($b->x - $a->x), 2) + pow(($b->y - $a->y),2) );

Output

Zero pad a number

Given the number 42, pad it to 8 characters like 00000042

ruby

42.to_s.rjust(8,"0")

"%08d" % 42

java

String formatted = new DecimalFormat("00000000").format(42);

String formatted = String.format("%08d", 42);

perl

sprintf("%08d", 42);

groovy

formatted = new DecimalFormat('00000000').format(42)

formatted = 42.toString().padLeft(8, '0')

// to stdout
printf "%08d\n", 42
// to a string
formatted = sprintf("%08d", 42)

formatted = String.format("%08d", 42)

scala

val formatted = String.format("%08d", int2Integer(42))

printf("%08d\n", 42)

python

"%08d" % 42

cpp

String^ formatted = Convert::ToString(42)->PadLeft(8, '0');

String^ formatted = String::Format("{0,8:D8}", 42);

std::printf("%08d", 42);

std::ostringstream os;
os << std::setw(8) << std::setfill('0') << 42 << std::ends;
std::cout << os.str() << std::endl;

std::cout << boost::format("%|08|") % 42 << std::endl;

fsharp

printfn "%08d" 42

let formatted = sprintf "%08d" 42
printfn "%s" formatted

let buffer = new StringBuilder()
Printf.bprintf buffer "%08d" 42
printfn "%s" (buffer.ToString())

let formatted = String.Format("{0,8:D8}", 42)
Console.WriteLine(formatted)

let formatted = Convert.ToString(42).PadLeft(8, '0')
Console.WriteLine(formatted)

erlang

Formatted = io_lib:format("~8..0B", [42]),

io:format("~8..0B~n", [42]).

ocaml

Printf.printf "%08d" 42;;

let s = Printf.sprintf "%08d" 42 in
print_string s;;

csharp

string.Format("{0,8:D8}", 42);

php

echo str_pad(42, 8, 0, STR_PAD_LEFT);

printf("%08d", 42);

Right Space pad a number

Given the number 1024 right pad it to 6 characters "1024 "

ruby

num = 1024
s = 1024.to_s
puts s + (6-s.length) * " "

java

private static String spaces(int spaces) {
StringBuffer sb = new StringBuffer();
for(int i=0; i<spaces; i++) {
sb.append(' ');
}
return sb.toString();
}

private static String rightPad(int number, int spaces) {
String numberString = String.valueOf(number);
return numberString + spaces(spaces - numberString.length());
}

String text = StringUtils.rightPad(String.valueOf(1024), 6)

String formatted = String.format("%-6d", 1024);

perl

sprintf("%-6d", 1024);

groovy

println 1024.toString().padRight(6)

formatted = sprintf("%-6d", 1024)

scala

val formatted = String.format("%-6d", int2Integer(1024))

printf("%-6d\n", 1024)

python

"%-6s" % 1024

cpp

String^ formatted = Convert::ToString(1024)->PadRight(6);

String^ formatted = String::Format("{0,-6:D}", 1024);

std::printf("%-6d\n", 1024);

std::ostringstream os;
os << std::setw(6) << std::setfill(' ') << std::left << 1024 << std::ends;
std::cout << os.str() << std::endl;

std::cout << boost::format("%|-6|") % 1024 << std::endl;

fsharp

printfn "%-6d" 1024

let formatted = String.Format("{0,-6:D}", 1024)
Console.WriteLine(formatted)

let formatted = Convert.ToString(1024).PadRight(6)
Console.WriteLine(formatted)

erlang

Formatted = io_lib:format("~-6B", [1024]),

io:format("~-6B~n", [1024]).

ocaml

Printf.printf "%-6i" 1024;;

csharp

public class NumberRightPadding {
public static void Main() {
string withStringDotFormat = string.Format("{0,-6}", 1024);
string withToStringDotPadRight = 1024.ToString().PadRight(6);
}
}

php

echo str_pad(1024, 6, " ");

printf("%s ", 1024);

Format a decimal number

Format the number 7/8 as a decimal with 2 places: 0.88

ruby

(7.0/8.0*100).round/100.0

java

String formatted = String.format("%3.2f", 7./8.);

perl

sprintf("%.2f", 7/8);

groovy

def result = 7/8
println result.round(new MathContext(2))

def result = 7/8
printf "%.2g", result

new Double(7/8).round(2)

scala

val formatted = String.format("%3.2f", double2Double(7./8.))

printf("%3.2f\n", 7./8.)

python

"%.2f" % (7 / 8.0)

cpp

String^ formatted = String::Format("{0,3:F2}", result);

Console::WriteLine("{0,3:F2}", (7. / 8.));

std::printf("%3.2f\n", result);

std::ostringstream os;
os.width(3); os.fill('0'); os.setf(std::ios::fixed|std::ios::showpoint); os.precision(2);
os << result << std::ends;
std::cout << os.str() << std::endl;

std::cout << boost::format("%|3.2f|") % result << std::endl;

fsharp

printfn "%3.2f" (0.7 / 0.8)

let formatted = String.Format("{0,3:F2}", (0.7 / 0.8))
Console.WriteLine(formatted)

erlang

Formatted = io_lib:format("~.2f", [7/8]),

io:format("~.2f~n", [7/8]).

ocaml

Printf.printf "%4.2f" (7. /. 8.);;

let s = Printf.sprintf "%4.2f" (7. /. 8.) in
print_string s;;

csharp

public class FormatDecimal {
public static void Main() {
decimal result = decimal.Round( 7 / 8m, 2);
System.Console.WriteLine(result);
}
}

php

printf("%.2g", 7/8);

Left Space pad a number

Given the number 73 left pad it to 10 characters " 73"

ruby

73.to_s.rjust(10)

java

private static String spaces(int spaces) {
StringBuffer sb = new StringBuffer();
for(int i=0; i<spaces; i++) {
sb.append(' ');
}
return sb.toString();
}

private static String leftPad(int number, int spaces) {
String numberString = String.valueOf(number);
return spaces(spaces - numberString.length()) + numberString;
}

String formatted = String.format("%10d", 73);

perl

sprintf("%10d", 73);

groovy

println 73.toString().padLeft(10)

printf "%10d\n", 73

scala

val formatted = String.format("%10d", int2Integer(73))

printf("%10d\n", 73)

python

"%10s" % 73

cpp

String^ formatted = Convert::ToString(73)->PadLeft(10);

String^ formatted = String::Format("{0,10:D}", 73);

std::printf("%10d\n", 73);

std::ostringstream os;
os << std::setw(10) << std::setfill(' ') << 73 << std::ends;
std::cout << os.str() << std::endl;

std::cout << boost::format("%|10|") % 73 << std::endl;

fsharp

let formatted = sprintf "%10d" 73
printfn "%s" formatted

let formatted = String.Format("{0,10:D}", 73)
Console.WriteLine(formatted)

let formatted = Convert.ToString(73).PadLeft(10)
Console.WriteLine(formatted)

erlang

Formatted = io_lib:format("~10B", [73]),

io:format("~10B~n", [73]).

ocaml

Printf.printf "%10d" 73;;

csharp

public class NumberLeftPadding {
public static void Main() {
string withStringDotFormat = string.Format("{0,10}", 73);
string withToStringDotPadLeft = 73.ToString().PadLeft(10);
}
}

php

echo str_pad(73, 10, " ", STR_PAD_LEFT);

printf("%10d", 73);

Random

Generate a random integer in a given range

Produce a random integer between 100 and 200 inclusive

ruby

randomInt = rand(200-100+1)+100;

java

Random random = new Random();
int randomInt = random.nextInt(200-100+1)+100;

perl

my $range = 100;
my $minimum = 100;

my $random_number = int(rand($range)) + $minimum;

print "$random_number\n";

groovy

random = new Random()
randomInt = random.nextInt(200-100+1)+100

scala

val rnd = new GenRandInt(100, 200)
val randomInt = rnd.next

val rnd = new scala.util.Random
val range = 100 to 200
println(range(rnd.nextInt(range length)))

python

import random
random.randint(100, 200)

# uses best entropy source available (e.g. /dev/urandom, CryptGenRandom, ...)

import random
print random.SystemRandom().randint(100,200)

cpp

Random^ rnd = gcnew Random;
int rndInt = rnd->Next(100, 201);

std::srand(std::time(NULL));

unsigned lb = 100, ub = 200;
unsigned rnd = lb + (rand() % ((ub - lb) + 1));

typedef boost::uniform_int<> Distribution;
typedef boost::mt19937 RNG;

Distribution distribution(100, 200);
RNG rng; rng.seed(std::time(NULL));
boost::variate_generator<RNG&, Distribution> generator(rng, distribution);

unsigned rnd = generator();

fsharp

let rnd = new Random()
let rndInt = rnd.Next(100, 201)

erlang

RandomInt = gen_rand_integer(100, 200),

ocaml

Random.self_init ();;
let a = 100 and b = 200 in
Random.int ( b - a + 1 ) + a;;

csharp

System.Random r = new System.Random();
int random = r.Next(100,201);

php

$r = mt_rand(100, 200);

Generate a repeatable random number sequence

Initialise a random number generator with a seed and generate five decimal values. Reset the seed and produce the same values.

ruby

srand(12345)
first = (1..5).collect {rand}
srand(12345)
second = (1..5).collect {rand}
puts first == second

java

int[] arr1 = genFillRand(new int[5], new Random(12345), 100, 200);
int[] arr2 = genFillRand(new int[5], new Random(12345), 100, 200);

for (int[] arr : new int[][]{ arr1, arr2 }) { for (int i : arr) System.out.printf("%d ", i); System.out.println(); }

perl

srand(12345);
@list1 = map(int(rand(100)+1), (1..5));

srand(12345);
@list2 = map(int(rand(100)+1), (1..5));

print join(', ', @list1) . "\n";
print join(', ', @list2) . "\n";

groovy

random = new Random(12345)
orig = (1..5).collect { random.nextInt(200-100+1)+100 }
random = new Random(12345)
repeat = (1..5).collect { random.nextInt(200-100+1)+100 }
assert orig == repeat

scala

val rnd = new scala.util.Random(12345)
(1 until 6) foreach { (_) => printf("%d ", 100 + rnd.nextInt(200)) } ; println()

rnd.setSeed(12345)
(1 until 6) foreach { (_) => printf("%d ", 100 + rnd.nextInt(200)) } ; println()

python

import random

random.seed(12345)
list1 = [random.randint(1,10) for x in range(5)]

random.seed(12345)
list2 = [random.randint(1,10) for x in range(5)]

assert(list1==list2)

cpp

void printAction(int i) { Console::Write("{0} ", i); }

array<int>^ genFillRand(array<int>^ arr, Random^ rnd, int lb, int ub)
{
for (int i = 0; i < arr->Length; ++i) arr[i] = rnd->Next(lb, ub + 1); return arr;
}

int main()
{
array<int>^ arr1 = genFillRand(gcnew array<int>(5), gcnew Random(12345), 100, 200);
array<int>^ arr2 = genFillRand(gcnew array<int>(5), gcnew Random(12345), 100, 200);

Action<int>^ print = gcnew Action<int>(printAction);
Array::ForEach<int>(arr1, print); Console::WriteLine();
Array::ForEach<int>(arr2, print); Console::WriteLine();
}

typedef boost::uniform_int<> Distribution;
typedef boost::mt19937 RNG;

Distribution distribution(100, 200);
RNG rng;
boost::variate_generator<RNG&, Distribution> generator(rng, distribution);

rng.seed(42L);
std::generate_n(std::ostream_iterator<unsigned>(std::cout, " "), 5, generator);

rng.seed(42L);
std::cout << std::endl;
std::generate_n(std::ostream_iterator<unsigned>(std::cout, " "), 5, generator);

fsharp

let (seed, lb, ub) = (12345, 100, 200)

let mutable rnd = new Random(seed)
for i = 1 to 5 do printf "%d " (rnd.Next(lb, ub + 1)) done ; printfn ""

rnd <- new Random(seed)
for i = 1 to 5 do printf "%d " (rnd.Next(lb, ub + 1)) done ; printfn ""

erlang

setRNG(RNGState),
io:format("~w~n", [lists:map(fun (_) -> gen_rand_integer(100, 200) end, lists:seq(1, 5))]),

setRNG(RNGState),
io:format("~w~n", [lists:map(fun (_) -> gen_rand_integer(100, 200) end, lists:seq(1, 5))]).

ocaml

let random_stream seed =
Random.init seed;
let state = ref (Random.get_state ()) in
Stream.from
(fun x ->
Random.set_state !state;
let res = Random.float 1. in
state := Random.get_state ();
Some res);;

Stream.npeek 5 (random_stream 1);;
Stream.npeek 5 (random_stream 1);;

csharp

using System;

public class RepeatableRandom {
public static void Main() {
var r = new Random(12); // seed is 12

for (int i = 0; i < 5; i++)
Console.WriteLine(r.Next());

r = new Random(12);

for (int i = 0; i < 5; i++)
Console.WriteLine(r.Next());
}
}

php

mt_srand(9876);
$r1 = array();
foreach(range(1,5) as $i) {
$r1[$i] = mt_rand(1,100);
}
mt_srand(9876);
$r2 = array();
foreach(range(1,5) as $i) {
$r2[$i] = mt_rand(1,100);
}

Regex

Matching

Check if a string matches a regular expression

Display "ok" if "Hello" matches /[A-Z][a-z]+/

ruby

puts "ok" if ("Hello"=~/^[A-Z][a-z]+$/)

java

if ("Hello".matches("[A-Z][a-z]+")) {
System.out.println("ok");
}

perl

print 'ok' if ('Hello' =~ /[A-Z][a-z]+/);

groovy

if ("Hello" =~ /[A-Z][a-z]+/) println 'ok'

if ("Hello".find(/[A-Z][a-z]+/)) println 'ok'

// with precompiled regex
def regex = ~/[A-Z][a-z]+/
if ("Hello".find(regex)) println 'ok'

// with precompiled regex
def regex = ~/[A-Z][a-z]+/
if ("Hello".matches(regex)) println 'ok'

if ("Hello".matches("[A-Z][a-z]+")) println 'ok'

scala

if ("Hello".matches("[A-Z][a-z]+")) println("ok")

python

found = re.match(r'[A-Z][a-z]+', 'Hello')
if found:
print 'ok'

cpp

if ((gcnew Regex("[A-Z][a-z]+"))->IsMatch("Hello")) Console::WriteLine("ok");

if (Regex::IsMatch("Hello", "[A-Z][a-z]+")) Console::WriteLine("ok");

Regex^ rx = gcnew Regex("[A-Z][a-z]+");
if (rx->IsMatch("Hello")) Console::WriteLine("ok");

fsharp

if (Regex.IsMatch("Hello", "[A-Z][a-z]+")) then printfn "ok"

erlang

String = "Hello", Regexp = "[A-Z][a-z]+",
is_match(String, Regexp) andalso (begin io:format("ok~n"), true end).

case re:run("Hello", "[A-Z][a-z]+") of {match, _} -> ok end.

ocaml

if Str.string_match (Str.regexp "[A-Z][a-z]+") "Hello" 0
then print_string "ok";;

csharp

if (Regex.IsMatch("Hello", "[A-Z][a-z]+"))
{
Console.WriteLine("ok");
}

php

if(ereg('[A-Za-z]+', 'Hello')) {
echo "ok";
}

if(preg_match('/[A-Za-z]+/', 'Hello')>0) {
echo "ok";
}

Check if a string matches with groups

Display "two" if "one two three" matches /one (.*) three/

ruby

puts $1 if "one two three"=~/^one (.*) three$/

java

Pattern pattern = Pattern.compile("one (.*) three");
Matcher matcher = pattern.matcher("one two three");
if (matcher.matches()) {
System.out.println(matcher.group(1));
}

perl

print $1 if "one two three"=~/^one (.*) three$/

groovy

matcher = ("one two three" =~ /one (.*) three/)
if (matcher) println matcher[0][1]

match = "one two three".find("one (.*) three") { it[1] }
if (match) println match

scala

val m = Pattern.compile("one (.*) three").matcher("one two three")
if (m.matches) println(m.group(1))

python

match = re.match(r'one (.*) three', 'one two three')
if match:
print match.group(1)

cpp

Match^ match = Regex::Match("one two three", "one (.*) three");
if (match->Success) Console::WriteLine("{0}", match->Groups[1]->Captures[0]);

fsharp

let regmatch = (Regex.Match("one two three", "one (.*) three"))
if regmatch.Success then (printfn "%s" (regmatch.Groups.[1].Captures.[0].ToString()))

erlang

case re:run("one two three", "one (.*) three", [{capture, [1], list}]) of {match, Res} -> hd(Res) end.

csharp

using System;
using System.Text.RegularExpressions;

public class RegexBackReference {
public static void Main() {
var oneTwoThree = "one two three";
var pattern = "one (.*) three";

Match match = Regex.Match(oneTwoThree, pattern);

// group 0 is the entire match. 1 is the first backreference
Console.WriteLine(match.Groups[1]);
}
}

php

preg_match('/one (.*) three/', 'one two three', $matches);
echo $matches[1];

ereg('one (.*) three', 'one two three', $regs);
echo $regs[1];

Searching

Check if a string contains a match to a regular expression

Display "ok" if "abc 123 @#$" matches /\d+/

ruby

puts "ok" if (text=~/\d+/)

java

Pattern pattern = Pattern.compile("\\d+");
Matcher matcher = pattern.matcher(text);
if (matcher.find()) {
System.out.println("ok");
}

perl

print "ok" if ("abc 123 @#\$" =~ m/\d+/)

groovy

if ('abc 123 @#$' =~ /\d+/) println 'ok'

if ('abc 123 @#$'.find(/\d+/)) println 'ok'

scala

if (Pattern.compile("\\d+").matcher("abc 123 @#$").find) println("ok")

python

found = re.search(r'\d+', 'abc 123 @#$')
if found:
print 'ok'

cpp

if (Regex::IsMatch("abc 123 @#$", "\\d+")) Console::WriteLine("ok");

fsharp

if (Regex.IsMatch("abc 123 @#$", "\\d+")) then printfn "ok"

erlang

% Erlang uses 'egrep'-compatible regular expressions, so shortcuts like '\d' not supported
String = "abc 123 @#$", Regexp = "[0-9]+",
is_match(String, Regexp) andalso (begin io:format("ok~n"), true end).

case re:run("abc 123 @#$", "\\d+") of {match, _} -> ok end.

csharp

if(System.Text.RegularExpressions.Regex.IsMatch("abc 123 @#$",@"\d+")){
Console.WriteLine("ok");
}

php

if (preg_match("/\d+/", "abc 123 @#$"))
echo "ok";

Loop through a string matching a regex and performing an action for each match

Create a list [fish1,cow3,boat4] when matching "(fish):1 sausage (cow):3 tree (boat):4" with regex /$(\w+)$:(\d+)/

ruby

list = text.scan(/$(\w+)$:(\d+)/).collect{|x| x.join}

list=[]
text.scan(/$(\w+)$:(\d+)/) {
list << $1+$2
}

java

List list = new ArrayList();
Pattern pattern = Pattern.compile("\$(\\w+)\$:(\\d+)");
Matcher matcher = pattern.matcher(text);
while(matcher.find()) {
list.add(matcher.group(1)+matcher.group(2));
}

perl

while ($text =~ /$(\w+)$:(\d+)/g) {
push @list, "$1$2"
}

groovy

list = (text =~ /$(\w+)$:(\d+)/).collect{ it[1] + it[2] }

list = []
text.eachMatch(/$(\w+)$:(\d+)/){
list << it[1] + it[2]
}

list = []
text.eachMatch(/$(\w+)$:(\d+)/){ m, name, number ->
list << "$name$number"
}

list = (text =~ /$(\w+)$:(\d+)/).collect{ all, name, num -> "$name$num" }

list = text.findAll(regex){ _, name, num -> "$name$num" }

list = text.findAll(regex){ it[1] + it[2] }

scala

val m = Pattern.compile("\$(\\w+)\$:(\\d+)").matcher("(fish):1 sausage (cow):3 tree (boat):4")
var list : List[String] = Nil

while (m.find) list = (m.group(1) + m.group(2)) :: list ; list = list.reverse

python

map(''.join, re.findall(r"$(\w+)$:(\d+)", "(fish):1 sausage (cow):3 tree (boat):4"))
--------------------------------------------------------------------------
(''.join(m.groups()) for m in re.finditer(r"$(\w+)$:(\d+)", "(fish):1 sausage (cow):3 tree (boat):4"))

cpp

Match^ match = Regex::Match("(fish):1 sausage (cow):3 tree (boat):4", "\$(\\w+)\$:(\\d+)");

while (match->Success)
{
list->Add(match->Groups[1]->Captures[0]->ToString() + match->Groups[2]->Captures[0]->ToString());
match = match->NextMatch();
}

fsharp

let list = new ResizeArray<string>()
let mutable regmatch = (Regex.Match("(fish):1 sausage (cow):3 tree (boat):4", "\$(\\w+)\$:(\\d+)"))

while regmatch.Success do
list.Add(regmatch.Groups.[1].Captures.[0].ToString() ^ regmatch.Groups.[2].Captures.[0].ToString())
regmatch <- regmatch.NextMatch()
done

for word in list do printfn "%s" word done

erlang

solve(S) ->
R = "\$(\\w+?)\$:(\\d+)",
{match, M} = re:run(S,R, [global, {capture, all_but_first, list}]),
[ A++N || [A, N] <- M].

csharp

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

public static class extensions {
public static IList<string> Map(this string me, string pattern, Func<Match, string> action){
IList<string> matches = new List<string>();
foreach (Match match in Regex.Matches(me,pattern)){
matches.Add(action(match));
}
return matches;
}
}

class Test
{
static void Main()
{
IList<string> list = "(fish):1 sausage (cow):3 tree (boat):4".Map(@"$(\w+)$:(\d+)", (m) => {return m.Groups[1].Value + m.Groups[2].Value;});
}
}

php

preg_match_all("/$(\w+)$:(\d+)/", "(fish):1 sausage (cow):3 tree (boat):4", $matches);
for ($i=0, $c=count($matches[0]); $i < $c; $i++) {
$list[] = $matches[1][$i].$matches[2][$i];
}

Replacing

Replace the first regex match in a string with a static string

Transform "Red Green Blue" into "R*d Green Blue" by replacing /e/ with "*"

ruby

p "Red Green Blue".sub(/e/,'*')

java

String replaced = "Red Green Blue".replaceFirst("e", "*");

perl

$text =~s/e/*/;

groovy

replaced = "Red Green Blue".replaceFirst("e", "*")

scala

val replaced = "Red Green Blue".replaceFirst("e", "*")

python

print re.sub(r'e', '*', 'Red Green Blue', 1)

cpp

String^ Replaced = (gcnew Regex("e"))->Replace("Red Green Blue", "*", 1);

fsharp

let replaced = ((new Regex("e")).Replace("Red Green Blue", "*", 1))
printfn "%s" replaced

erlang

{ok, Replaced, _} = regexp:sub("Red Green Blue", "e", "*"),

re:replace("Red Green Blue", "e", "*", [{return, list}]).

php

echo preg_replace('/e/', '*', "Red Green Blue", 1);

Replace all regex matches in a string with a static string

Transform "She sells sea shells" into "She X X shells" by replacing /se\w+/ with "X"

ruby

replaced = text.gsub(/se\w+/,"X")

java

String replaced = text.replaceAll("se\\w+", "X");

perl

$text = "She sells sea shells";
$text =~ s/se\w+/X/g;

groovy

replaced = text.replaceAll(/se\w+/,"X")

scala

val replaced = "She sells sea shells".replaceAll("se\\w+", "X")

python

transformed = re.sub(r'se\w+', 'X', 'She sells sea shells')

cpp

String^ Replaced = (gcnew Regex("se\\w+"))->Replace("She sells sea shells", "X");

String^ Replaced = Regex::Replace("She sells sea shells", "se\\w+", "X");

fsharp

let replaced = ((new Regex("se\\w+")).Replace("She sells sea shells", "X"))
printfn "%s" replaced

erlang

% Erlang uses 'egrep'-compatible regular expressions, so shortcuts like '\w' not supported
{ok, Replaced, _} = regexp:gsub("She sells sea shells", "se[A-Za-z0-9_]+", "X"),

re:replace("She sells sea shells", "se\\w+", "X", [global, {return, list}]).

php

echo preg_replace('/se\w+/', 'X', 'She sells sea shells');

Replace all regex matches in a string with a dynamic string

Transform "The {Quick} Brown {Fox}" into "The kciuQ Brown xoF" by reversing words in braces using the regex /\{(\w+)\}/.

ruby

"The {Quick} Brown {Fox}".gsub(/\{(\w+)\}/) {|s| s[1..-2].reverse }

java

Matcher m = Pattern.compile("\\{(\\w+)\\}").matcher("The {Quick} Brown {Fox}");
StringBuffer sb = new StringBuffer(32), rsb = new StringBuffer(8);

while (m.find())
{
rsb.replace(0, rsb.length(), m.group(1)); rsb.reverse(); m.appendReplacement(sb, rsb.toString());
}
m.appendTail(sb);

perl

$text = "The {Quick} Brown {Fox}";
$text =~ s/\{(\w+)\}/reverse($1)/ge;

groovy

replaced = "The {Quick} Brown {Fox}".replaceAll(/\{(\w+)\}/, { full, word -> word.reverse() } )

scala

val m = Pattern.compile("\\{(\\w+)\\}").matcher("The {Quick} Brown {Fox}")
val sb = new StringBuffer(32) ; val rsb = new StringBuffer(8)

while (m.find) { rsb.replace(0, rsb.length, m.group(1)) ; m.appendReplacement(sb, rsb.reverse.toString) }
m.appendTail(sb)

python

transformed = re.sub(r'\{(\w+)\}',
lambda match: match.group(1)[::-1],
'The {Quick} Brown {Fox}')

cpp

String^ Replaced = (gcnew Regex("{(\\w+)}"))->Replace("The {Quick} Brown {Fox}", gcnew MatchEvaluator(&RegRep::RepGroup));

String^ Replaced = Regex::Replace("The {Quick} Brown {Fox}", "{(\\w+)}", gcnew MatchEvaluator(&RegRep::RepGroup));

fsharp

open System
open System.Text.RegularExpressions
let reverseMatch (m:Match) =
String(m.Groups.[1].Value.ToCharArray() |> Array.rev)
let output = Regex.Replace("The {Quick} Brown {Fox}", @"\{(\w+)\}", reverseMatch)

erlang

% Erlang regular expressions lack both group capture and backreferences, thus this problem is not directly
% solvable. Presented solution is close, but not on-spec

String = "The {Quick} Brown {Fox}",
{match, FieldList} = regexp:matches(String, "\{([A-Za-z0-9_]+)\}"),

NewString = lists:foldl(fun ({Start, Length}, S) -> replstr(S, lists:reverse(string:substr(S, Start, Length)), Start) end, String, FieldList),

php

// We have to use the e-modifier
preg_replace("/\{(\w+)\}/e", "''.strrev('\\1').''", "The {Quick} Brown {Fox}");

Lists

Declaration

Define an empty list

Assign the variable "list" to a list with no elements

ruby

list = []

list = Array.new

java

List list = Collections.emptyList();

String[] list = {};

perl

@list = ();

groovy

list = []

// if a special kind of list is required
list = new LinkedList() // java style
LinkedList list = [] // statically typed
// using 'as' operator
list = [] as java.util.concurrent.CopyOnWriteArrayList

scala

val list = Nil

val list = List()

val list : List[String] = List()

python

list = []

cpp

Generic::List<String^>^ list = gcnew Generic::List<String^>();

std::list<std::string> list;

fsharp

let list = []

let list = List.empty

let list = new Generic.List<string>()

let list = new Generic.LinkedList<string>()

erlang

List = [],

ocaml

let list = [];;

csharp

var list = new List<object>();

php

$list = array();

haskell

let list = []

Define a static list

Define the list [One, Two, Three, Four, Five]

ruby

list = ['One', 'Two', 'Three', 'Four', 'Five']

list = %w(One Two Three Four Five)

java

List<String> numbers = new ArrayList<String>();
Collections.addAll(numbers, "One", "Two", "Three", "Four", "Five");

List numbers = new ArrayList();
numbers.add("One");
numbers.add("Two");
numbers.add("Three");
numbers.add("Four");
numbers.add("Five");

List numbers = Arrays.asList(new String[]{"One", "Two", "Three", "Four", "Five"});

String[] numbers = {"One", "Two", "Three", "Four", "Five"};

List numbers = new ArrayList(){{put("One"); put("Two"); put("Three"); put("Four"); put("Five"); }};

perl

@list = qw(One Two Three Four Five);

@list = ('One', 'Two', 'Three', 'Four', 'Five');

groovy

list = ['One', 'Two', 'Three', 'Four', 'Five']

// other variations
List<String> numbers1 = ['One', 'Two', 'Three', 'Four', 'Five']
String[] numbers2 = ['One', 'Two', 'Three', 'Four', 'Five']
numbers3 = new LinkedList(['One', 'Two', 'Three', 'Four', 'Five'])
numbers4 = ['One', 'Two', 'Three', 'Four', 'Five'] as Stack // Groovy 1.6+

scala

val list = "One" :: "Two" :: "Three" :: "Four" :: "Five" :: Nil

val list = List("One", "Two", "Three", "Four", "Five")

val list : List[String] = List("One", "Two", "Three", "Four", "Five")

python

list = ['One', 'Two', 'Three', 'Four', 'Five']
print list

cpp

array<String^>^ input = {"One", "Two", "Three", "Four", "Five"};
Generic::List<String^>^ list = gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) input);

Generic::List<String^>^ list = gcnew Generic::List<String^>();

list->Add("One");
list->Add("Two");
list->Add("Three");
list->Add("Four");
list->Add("Five");

std::string input[] = {"One", "Two", "Three", "Four", "Five"};
std::list<std::string> list(input, input + 5);

std::list<std::string> list;

list.push_back("One");
list.push_back("Two");
list.push_back("Three");
list.push_back("Four");
list.push_back("Five");

fsharp

let list = ["One"; "Two"; "Three"; "Four"; "Five"]

let list = (new Generic.LinkedList<string>([|"One"; "Two"; "Three"; "Four"; "Five"|]))

let list = (new Generic.LinkedList<string>())

list.AddFirst("One") ; list.AddLast("Five") ; list.AddBefore(list.Find("Five"), "Four")
list.AddAfter(list.Find("One"), "Two") ; list.AddAfter(list.Find("Two"), "Three")

let list = (new Generic.List<string>())

[|"One"; "Two"; "Three"; "Four"; "Five"|] |> Array.iter (fun x -> list.Add(x))

erlang

List = [one, two, three, four, five],

List = ['One', 'Two', 'Three', 'Four', 'Five'],

ocaml

let list = [ "One"; "Two"; "Three"; "Four"; "Five" ];;

csharp

IList<string> list = new string[]{"One","Two","Three","Four","Five"};

php

$list = array("One", "Two", "Three", "Four", "Five");

$list = array();
$list[] = "One";
$list[] = "Two";
$list[] = "Three";
$list[] = "Four";
$list[] = "Five";

<?php
$list = new SplFixedArray(5);

$list[0] = "One";
$list[1] = "Two";
$list[2] = "Three";
$list[3] = "Four";
$list[4] = "Five";
?>

haskell

let a = ["One", "Two", "Three", "Four", "Five"]

Output

Join the elements of a list, separated by commas

Given the list [Apple, Banana, Carrot] produce "Apple, Banana, Carrot"

ruby

string = fruit.join(', ')

java

StringBuffer sb = new StringBuffer();
for (Iterator it = fruit.iterator(); it.hasNext();) {
sb.append(it.next());
if (it.hasNext()) {
sb.append(", ");
}
}
String result = sb.toString();

StringBuilder sb = new StringBuilder(fruit.get(0));
for (String item : fruit.subList(1, fruit.size())) sb.append(", ").append(item);
String result = sb.toString();

String result = StringUtils.join(fruit, ", ");

perl

print join ', ', qw(Apple Banana Carrot);

# Longer and less efficient than join(), but illustrates
# Perl's foreach operator, which can be useful for
# less trivial problems with lists

@list = ('Apple', 'Banana', 'Carrot');
foreach $fruit (@list) {
print "$fruit,";
}
print "\n";

groovy

string = fruit.join(', ')

string = fruit.toString()[1..-2]

scala

val result =
((fruit.tail foldLeft (new StringBuilder(fruit.head))) {(acc, e) => acc.append(", ").append(e)}).toString

val result = fruit.mkString(",")

python

print ", ".join(['Apple', 'Banana', 'Carrot'])

cpp

String^ result = String::Join(L", ", fruit->ToArray());

fsharp

let result = String.Join(", ", [|"Apple"; "Banana"; "Carrot"|])

let result = (List.fold_left (fun acc item -> acc ^ (", " ^ item)) (List.hd fruit) (List.tl fruit))

let result = (List.fold_left (fun (acc : StringBuilder) (item : string) -> acc.Append(", ").Append(item)) (new StringBuilder(List.hd fruit)) (List.tl fruit)).ToString()

erlang

Result = string:join(Fruit, ", "),

Result = lists:foldl(fun (E, Acc) -> Acc ++ ", " ++ E end, hd(Fruit), tl(Fruit)),

ocaml

let list = [ "Apple"; "Banana"; "Carrot" ];;

let f str_so_far elem = str_so_far ^ ", " ^ elem in
let str = List.fold_left f list;;

print_string str;;

csharp

using System.Collections.Generic;
public class JoinEach {
public static void Main() {
var list = new List<string>() {"Apple", "Banana", "Carrot"};
System.Console.WriteLine( string.Join(", ", list.ToArray()) );
}
}

php

$string = implode(", ", $fruits);

Join the elements of a list, in correct english

Create a function join that takes a List and produces a string containing an english language concatenation of the list. It should work with the following examples:
join([Apple, Banana, Carrot]) = "Apple, Banana, and Carrot"
join([One, Two]) = "One and Two"
join([Lonely]) = "Lonely"
join([]) = ""

ruby

def join(arr)
return '' if not arr
case arr.size
when 0 then ''
when 1 then arr[0]
when 2 then arr.join(' and ')
else arr[0..-2].join(', ') + ', and ' + arr[-1]
end
end

java

private String join(List elements) {
if (elements == null || elements.size() == 0) {
return "";
} else if (elements.size() == 1) {
return elements.get(0).toString();
} else if (elements.size() == 2) {
return elements.get(0) + " and " + elements.get(1);
}
StringBuffer sb = new StringBuffer();
for (Iterator it = elements.iterator(); it.hasNext();) {
String next = (String) it.next();
if (sb.length() > 0) {
if (it.hasNext()) {
sb.append(", ");
} else {
sb.append(", and ");
}
}
sb.append(next);
}
return sb.toString();
}

System.out.println(join(fruit));

perl

sub myjoin {
$_ = join ', ', @_;
s/, ([^,]+)$/ and $1/;
return $_;
}

# Note: I don't think this meets the spec --Geoff

sub myjoin {
if ($#_ < 2) {
return join ' and ', @_;
} else {
return join(', ', @_[0..$#_-1]) . ' and ' . $_[-1];
}
}

# Note: I don't think this meets the spec --Geoff

# Previous "myjoin()" responses don't meet the spec of including
# the final comma before the "and" if the list has more than
# two elements...this is one way to meet that spec...it may
# not be the most efficient...

sub AnotherMyJoin {
my @list = @_;

if ($#list == -1) {return}
elsif ($#list == 0) {return $list[0]}
elsif ($#list == 1) {return $list[0].' and '.$list[1]}
else {
return join(", ", @list[0..$#list - 1]) . ', and '. $list[$#list];
}
}

# This is the long way, but it's kind of fun
# It illustrates the use of Perl's reverse()
# operator to work our way through the list
# elements backwards...I wrote this one before
# getting smart and looking at some of the other
# algorithms from the other languages. Still,
# it is only 12 lines of code vs 9 for my other
# solution if you disregard the comments.

sub myjoin {
my @list = reverse(@_); # Reverse original order of elements
my $retval;

# Make our exit here if we were passed an empty list
if ($#list == -1) {return}

# Loop through reversed elements in end-to-start order
for (0..$#list) {
# Add the reversed form of each element plus a space char
$retval .= reverse($list[$_]).' ';

# Add 'and' to lists with two or more elements
# placing it in between final and 'next to final'
$retval .= "dna " if ($#list > 0 and $_== 0);

# Add ',' to each element as long as there are more
# than two elements and the current element isn't the
# final element
$retval .= "," if ($#list > 1 and $_ != $#list);
}

# Remove what will end up as an extraneous leading space
chop($retval);

# Done looping, now reverse things back into correct order and return
$retval = reverse($retval);
return($retval);
}

groovy

def join(list) {
if (!list) return ''
switch(list.size()) {
case 1:
return list[0]
case 2:
return list.join(' and ')
default:
return list[0..-2].join(', ') + ', and ' + list[-1]
}
}

scala

def join(list : List[String]) : String = list match {
case List() => ""
case List(x) => x
case List(x,y) => x + " and " + y
case List(x,y,z) => x + ", " + y + ", and " + z
case _ => list(0) + ", " + join(list.tail)
}

python

def join(*x):
if len(x) <= 2:
return ' and '.join(x)
else:
return ', '.join(x[:-1] + ('and ' + x[-1],))

if __name__ == "__main__":
assert join("Apple", "Banana", "Carrot") == "Apple, Banana, and Carrot"
assert join("One", "Two") == "One and Two"
assert join("Lonely") == "Lonely"
assert join(*[]) == ""

cpp

Console::WriteLine(join(fruit));

fsharp

erlang

io:format("~s~n", [join(Fruit)]).

% ------

join([]) -> "";
join([W|Ws]) -> join(Ws, W).

join([], S) -> S;
join([W], S) -> join([], S ++ " and " ++ W);
join([W|Ws], S) -> join(Ws, S ++ ", " ++ W).

ocaml

let join list =
let rec join' list acc =
match list with
| [] -> ""
| [single] -> single
| one::[two] ->
if acc = "" then one ^ " and " ^ two
else acc ^ one ^ ", and " ^ two
| first::others -> join' others (acc ^ first ^ ", ")
in
join' list ""

csharp

using System.Collections.Generic;
using System.Linq;

public class CSharpListToEnglishList {
public string JoinAsEnglishList (List<string> words) {
switch (words.Count) {
case 0: return "";
case 1: return words[0];
case 2: return string.Format("{0} and {1}", words.ToArray());
default:
return JoinAsEnglishList( new List<string>() {
string.Join(", ", words.Take(words.Count - 1).ToArray()) + ",",
words.Last()
});
}
}
// Driver...
public static void Main() {
var joiner = new CSharpListToEnglishList();
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Apple", "Banana", "Carrot", "Orange" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Apple", "Banana", "Carrot" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "One", "Two" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Lonely" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>()) );
}
}

php

function ImplodeToEnglish($array) {
// sanity check
if (!$array || !count ($array))
return "";

// get last element
$last = array_pop($array);

// if it was the only element - return it
if (!count ($array))
return $last;

return implode(", ", $array)." and ".$last;
}
//example
ImplodeToEnglish(array("Apple", "Banana")); // returns: Apple and Banana

Produce the combinations from two lists

Given two lists, produce the list of tuples formed by taking the combinations from the individual lists. E.g. given the letters ["a", "b", "c"] and the numbers [4, 5], produce the list: [["a", 4], ["b", 4], ["c", 4], ["a", 5], ["b", 5], ["c", 5]]

ruby

common = [] ; [4, 5].each {|n| ['a', 'b', 'c'].each {|l| common << [l, n]}}

java

List<String> combinations = new ArrayList<String>();

for (int number : numbers)
for (String letter : letters)
combinations.add(letter + ":" + Integer.toString(number));

SortedSet<AbstractMap.SimpleImmutableEntry<String, Integer> > combinations =
new TreeSet<AbstractMap.SimpleImmutableEntry<String, Integer> >(new CombinationComparator());

for (int number : numbers)
for (String letter : letters)
combinations.add(new AbstractMap.SimpleImmutableEntry<String, Integer>(letter, Integer.valueOf(number)));

perl

@letters = qw(a b c);
@numbers = (4, 5);
@list = map { $number=$_; map [$_, $number], @letters; } @numbers;

@letters = qw(a b c);
@numbers = (4, 5);

for $number (@numbers) {
for $letter (@letters) {
push @list, [$letter, $number];
}
}

groovy

letters = ['a', 'b', 'c']
numbers = [4, 5]
combos = [letters, numbers].combinations()

scala

val combinations =
(numbers foldLeft List[Pair[String, Int]]()) { (acc : List[Pair[String, Int]], number : Int) =>
acc ::: (letters map { (letter : String) => Pair(letter : String, number : Int) }) }

def product(set1 : List[_], set2 : List[_]) : List[Pair[_, _]] =
{
val p = new mutable.ArrayBuffer[Pair[_, _]]()
for (e1 <- set1) for (e2 <- set2) p += Pair(e1, e2)
p.toList
}

// ------

val combinations =
product(numbers, letters) map { (c) => c match { case Pair(number, letter) => Pair(letter, number) } }

val letters = List('a', 'b', 'c')
val numbers = List(4, 5)
for { l <- letters; n <- numbers } yield (l,n)

python

[(x, y) for y in [1,2] for x in ['a','b','c']]

import itertools
[x for x in itertools.product(["a", "b", "c"], [4, 5])]

cpp

Specialized::StringCollection^ combinations = gcnew Specialized::StringCollection;

for each(int number in numbers)
for each(String^ letter in letters)
combinations->Add(makeCombo(letter, number));

fsharp

let combinations = (List.fold_left (fun acc number -> acc @ (List.map (fun letter -> (letter, number)) letters)) [] numbers)

erlang

Combinations =
lists:foldl(fun (Number, Acc) -> Acc ++ lists:map(fun (Letter) -> {Letter, Number} end, Letters) end, [], Numbers),

Combinations = lists:keysort(2, sofs:to_external(sofs:product(sofs:set(Letters), sofs:set(Numbers))))

[[A, B] || A <- ["a", "b", "c"], B <- [4, 5]].

csharp

using System.Collections.Generic;
public class ListCombiner {
public static void Main() {
var letters = new List<char>() { 'a', 'b', 'c' };
var numbers = new List<int>() { 1, 2, 3 };

// result is a list that contaings lists of objects
var result = new List<List<object>>();
foreach (var l in letters) {
foreach (var n in numbers) {
result.Add(new List<object>() { l, n });
}
}
}
}

php

foreach ($short as $s) {
foreach ($long as $l) {
$list[] = array($l, $s);
}
}

Access

Fetch an element of a list by index

Given the list [One, Two, Three, Four, Five], fetch the third element ('Three')

ruby

list = ['One', 'Two', 'Three', 'Four', 'Five']
list[2]

['One', 'Two', 'Three', 'Four', 'Five'].fetch(2)

list = ['One', 'Two', 'Three', 'Four', 'Five']
list.at(2)

['One', 'Two', 'Three', 'Four', 'Five'][2] # <= note the [2] at end of array

java

String result = list.get(2);

perl

qw(One Two Three Four Five)[2];

@list = qw(One Two Three Four Five);
$list[2];

groovy

list = ['One', 'Two', 'Three', 'Four', 'Five']
result = list[2] // index starts at 0

scala

val result = list(2)

python

list = ['One', 'Two', 'Three', 'Four', 'Five']
list[2]

cpp

String^ result = list[2];

fsharp

let result = List.nth ["One"; "Two"; "Three"; "Four"; "Five"] 2

erlang

Result = lists:nth(3, List),

Result = element(3, list_to_tuple(List)),

{Left, _} = lists:split(3, List), Result = lists:last(Left),

Result = nth0(2, List),

ocaml

let third = List.nth [ "One"; "Two"; "Three"; "Four"; "Five" ] 3;;

csharp

string[] items = new string[] { "One", "Two", "Three", "Four", "Five" };
List<string> list = new List<string>(items);
string third = list[2]; // "Three"

// Make sure you import the System.Linq namespace.
// This is not the preferred way of indexing if you are using Lists.
string[] items = new string[] { "One", "Two", "Three", "Four", "Five" };
IEnumerable<string> list = new List<string>(items);
string third = list.ElementAt(2); // Three

php

$list = array("One", "Two", "Three", "Four", "Five");
$three = $list[2];

haskell

let a = [1..5]
let b = a !! 2
print b

Fetch the last element of a list

Given the list [Red, Green, Blue], access the last element ('Blue')

ruby

['Red', 'Green', 'Blue'][-1]

['Red', 'Green', 'Blue'].at(-1)

['Red', 'Green', 'Blue'].last

['Red', 'Green', 'Blue'].fetch(-1)

java

String result = list.get(list.size() - 1);

perl

qw(Red Green Blue)[-1];

@list = qw(Red Green Blue);
$list[-1];

groovy

list = ['Red', 'Green', 'Blue']
result = list[-1]

scala

val result = list.last

val result = (list.drop(list.length - 1)).head

python

list = ['Red', 'Green', 'Blue']
list[-1]

cpp

String^ result = list[list->Count - 1];

fsharp

let last list =
let rec last' list' =
match list' with
| [x] -> x
| x :: xs -> last' xs
if List.is_empty list then failwith "empty list" else last' list

// ------

let result = last list

let result = (List.nth list ((List.length list) - 1))

let result = (List.hd (List.rev list))

erlang

Result = lists:last(List),

Result = last(List),

Result = hd(lists:reverse(List)),

Result = lists:nth(length(List), List),

ocaml

let list = [ "Red"; "Green"; "Blue" ] in
let last = List.nth list ( (List.length list) - 1 );;

let list = [ "Red"; "Green"; "Blue" ] in
let last = List.hd (List.rev list);;

csharp

string[] items = new string[] { "Red", "Green", "Blue" };
List<string> list = new List<string>(items);
string last = list[list.Count - 1]; // "Blue"

// Make sure you import the System.Linq namespace.
// This is not the preferred way of finding the last element if you are using Lists.
string[] items = new string[] { "Red", "Green", "Blue" };
IEnumerable<string> list = new List<string>(items);
string last = list.Last(); // "Blue"

php

$list = array("Red", "Green", "Blue");
$last = array_pop($list);

// Be aware of that $list only contains two elements now - not three

$list = array("Red", "Green", "Blue");
$last = $list[count($list)-1];

Find the common items in two lists

Given two lists, find the common items. E.g. given beans = ['broad', 'mung', 'black', 'red', 'white'] and colors = ['black', 'red', 'blue', 'green'], what are the bean varieties that are also color names?

ruby

common = (beans.intersection(colors)).to_a

java

List beans = Arrays.asList(new String[]{"broad", "mung", "black", "red", "white"});
List colors = Arrays.asList(new String[]{"black", "red", "blue", "green"});

List common = ListUtils.intersection(beans, colors);

perl

@beans = qw(broad mung black red white);
@colors = qw(black red blue green);
@seen{@beans} = ();
for (@colors) {
push(@intersection, $_) if exists($seen{$_});
}
print join(', ', @intersection);

groovy

beans = ['broad', 'mung', 'black', 'red', 'white']
colors = ['black', 'red', 'blue', 'green']
common = beans.intersect(colors)
assert common == ['black', 'red']

scala

val beans = "broad" :: "mung" :: "black" :: "red" :: "white" :: Nil
val colors = "black" :: "red" :: "blue" :: "green" :: Nil
val common = beans intersect colors

python

beans = ['broad', 'mung', 'black', 'red', 'white']
colors = ['black', 'red', 'blue', 'green']

common = [b for b in beans if b in colors]

beans = ['broad', 'mung', 'black', 'red', 'white']
colors = ['black', 'red', 'blue', 'green']

common = set(beans) & set(colors)

cpp

array<String^>^ inbeans = {"broad", "mung", "black", "red", "white"};
Generic::ICollection<String^>^ beans = makeSET<String^>(gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) inbeans));

array<String^>^ incolors = {"black", "red", "blue", "green"};
Generic::ICollection<String^>^ colors = makeSET<String^>(gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) incolors));

Generic::ICollection<String^>^ result = intersectSET<String^>(beans, colors);

fsharp

let beans = (Set.of_list ["broad"; "mung"; "black"; "red"; "white"])
let colors = (Set.of_list ["black"; "red"; "blue"; "green"])
let common = (Set.intersect beans colors)

erlang

Beans = sets:from_list([broad, mung, black, red, white]), Colors = sets:from_list([black, red, blue, green]),

Common = sets:to_list(sets:intersection(Beans, Colors)),

ocaml

let beans = ["broad"; "mung"; "black"; "red"; "white"]

let colors = ["black"; "red"; "blue"; "green"]

let f common c = if List.mem c beans then c::common else common

let common = List.fold_left f [] colors;;

(* common will contain a list with the common elements *)

csharp

// Make sure you import the System.Linq namespace.
// This example uses arrays as the underlying implementation, but any IEnumerable type can be used - including List.
IEnumerable<string> beans = new string[] { "beans", "mung", "black", "red", "white" };
IEnumerable<string> colors = new string[] { "black", "red", "blue", "green" };
var intersect = beans.Intersect(colors); // ['red', 'black']

php

$result = array_intersect($beans, $colors);
sort($result); // just to clean it up :)

Display the unique items in a list

Display the unique items in a list, e.g. given ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18], display the unique elements, i.e. with duplicates removed.

ruby

ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
p ages.uniq

ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
ages.uniq!
p ages

ages = (Set.new [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]).to_a
p ages

java

Set<Integer> ages = new TreeSet<Integer>(Arrays.asList(new Integer[]{18, 16, 17, 18, 16, 19, 14, 17, 19, 18}));

System.out.println(ages);

perl

@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
@seen{@ages} = ();
@unique = keys %seen;
print join(', ', @unique);

@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
@unique = grep(!$seen{$_}++, @ages);
print join(', ', @unique);

@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
print join(', ', grep(!$seen{$_}++, @ages));

@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
for (@ages) {
push(@unique, $_) unless $seen{$_}++;
}
print join(', ', @unique);

use List::MoreUtils qw(uniq);

@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
print join(', ', uniq(@ages));

groovy

ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
println ages.unique()

ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
unique = ages as Set
println unique

scala

val ages = (18 :: 16 :: 17 :: 18 :: 16 :: 19 :: 14 :: 17 :: 19 :: 18 :: Nil) removeDuplicates

python

ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]

unique_ages = list(set(ages))

cpp

array<int>^ input = {18, 16, 17, 18, 16, 19, 14, 17, 19, 18};
Generic::List<int>^ ages = gcnew Generic::List<int>((Generic::IEnumerable<int>^) input);

Generic::ICollection<int>^ result = makeSET<int>(ages);

fsharp

(Set.of_list [18; 16; 17; 18; 16; 19; 14; 17; 19; 18]) |> Set.iter (fun age -> printf "%d, " age)

erlang

Ages = sets:to_list(sets:from_list([18, 16, 17, 18, 16, 19, 14, 17, 19, 18])), io:format("~w~n", [Ages]).

lists:usort([18, 16, 17, 18, 16, 19, 14, 17, 19, 18]).

ocaml

let ages = [18; 16; 17; 18; 16; 19; 14; 17; 19; 18]

let f res e = if List.mem e res then res else e::res

let unique = List.fold_left f [] ages;;

csharp

using System.Collections.Generic;
using System.Linq;
public class UniqueElements {
public static void Main() {
var list = new List<int>() { 18, 16, 17, 18, 16, 19, 14, 17, 19, 18 };
var uniques = list.Distinct();
}
}

php

$ages = array(18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
$ages = array_unique($ages);
// be aware of that $ages[6] will print 14

Modification

Remove an element from a list by index

Given the list [Apple, Banana, Carrot], remove the first element to produce the list [Banana, Carrot]

ruby

['Apple', 'Banana', 'Carrot'].shift

fruit.delete_at(0)

java

list.remove(0);

perl

@list = qw(Apple Banana Carrot);
shift @list;

@list = qw(Apple Banana Carrot);
$offset = 0;
splice(@list, $offset, 1);

groovy

// to produce a new list
newlist = list.tail() // for 'Apple' at start
newlist = list - 'Apple' // for 'Apple' anywhere

// mutate original list
list.remove(0)

scala

val (fl, fr) = fruit.splitAt(0) ; fruit = fl ::: fr.tail

fruit = fruit.tail

fruit = fruit.drop(1)

fruits = fruits.remove(fruits.indexOf(_) == 0)

python

myList = ['Apple', 'Banana', 'Carrot']
print myList
del myList[0]
# or
myList.pop(0) # returns 'Apple'
print myList

cpp

fruit->RemoveAt(0);

fsharp

let split_at list n =
let rec split_at' list' n' left right =
match list' with
| [] -> (List.rev left, List.rev right)
| x :: xs -> if n' <= n then split_at' xs (n' + 1) (x :: left) right else split_at' xs (n' + 1) left (x :: right)
split_at' list 0 [] []

// ------

let (_, right) = split_at fruit 0

let drop list n =
if n <= 0 then
list
else
let (_, right) = split_at list (n - 1)
right

// ------

let result = (drop fruit 1)

erlang

Result = tl(List),

[_|Result] = List,

N = 1, {Left, Right} = lists:split(N - 1, List), Result = Left ++ tl(Right),

Result = drop(1, List),

ocaml

let remove i list =
let rec rem i list' acc =
match list' with
| h::t when i > 0 -> rem (i-1) t (h::acc)
| h::t when i = 0 -> (List.rev acc)@t
| [] -> List.rev acc (* not enough elements *)
in
rem i list []

php

$list = array("Apple", "Banana", "Carrot");
unset($list[0]);

// Be aware of that $list[0] isn't set. "Banana" is still $list[1]

$list = array("Apple", "Banana", "Carrot");
array_shift($list);

// Be aware of that $list[0] is set to "Banana"

Remove the last element of a list

ruby

list = ['Apple', 'Banana', 'Carrot']
list.delete_at(-1)

list = ['Apple', 'Banana', 'Carrot']
list.pop

java

list.remove(list.size() - 1);

perl

pop @list;

groovy

list = ['Apple', 'Banana', 'Carrot']
// to produce a new list
newlist = list[0,1]
// to modify original list
list.remove(2)

scala

fruit = fruit.init

fruit = fruit.take(fruit.length - 1)

python

myList = ['Apple', 'Banana', 'Carrot']
myList.pop()

cpp

fruit->RemoveAt(fruit->Count - 1);

fsharp

let take list n =
if n <= 0 then
list
else
let (left, _) = split_at list (n - 1)
left

// ------

let result = (take fruit ((List.length fruit) - 1))

let but_last list =
let rec but_last' list' acc =
match list' with
| [x] -> List.rev acc
| x :: xs -> but_last' xs (x :: acc)
if List.is_empty list then [] else but_last' list []

// ------

let result = (but_last fruit)

erlang

Result = init(List),

Result = take(length(List) - 1, List),

Result = lists:reverse(tl(lists:reverse(List))),

ocaml

let remove_last list =
match (List.rev list) with
| h::t -> List.rev t
| [] -> []

php

$list = array("Apple", "Banana", "Carrot");
unset($list[count($list)-1]);

// Be aware of that
// $list[] = "Orange";
// will be $list[3] and not $list[2]

$list = array("Apple", "Banana", "Carrot");
array_pop($list);

Rotate a list

Given a list ["apple", "orange", "grapes", "bananas"], rotate it by removing the first item and placing it on the end to yield ["orange", "grapes", "bananas", "apple"]

ruby

items = ["apple", "orange", "grapes", "bananas"]
items << first = items.shift

# items is rotated
# first contains the first value in the list

java

list.add(list.remove(0));

perl

@list = qw(apple, orange, grapes, bananas);
push @list, shift @list;

@list = qw(apple orange grapes bananas);
@list = @list[1..$#list,0];

groovy

first = items.head()
items = items.tail() + first

items = items[1..-1] + items[0]

items = items + items.remove(0)

scala

items = items.tail ::: List(items.head)

items = (items.head :: ((items.tail).reverse)).reverse

python

l = ["apple", "orange", "grapes", "bananas"]
first, l = l[0], l[1:] + l[:1]

fruit = ['apple', 'orange', 'grapes', 'bananas']
fruit.append(fruit.pop(0))

cpp

fruit->Add(fruit[0]); fruit->RemoveAt(0);

fsharp

let rotate list n =
if n <= 0 then
list
else
let (left, right) = split_at list (n - 1)
right @ left

// ------

let result = (rotate fruit 1)

erlang

N = 1, {Left, Right} = lists:split(N, List), Result = Right ++ Left,

N = 1, Result = rotate(N, List),

ocaml

let rotate list =
match list with
| head::tail -> tail@[head]
| [] -> []

php

$list = array("Apple", "Orange", "Grapes", "Banana");
$first = array_shift($list); //get and remove the first
array_push($list, $first); //prepend the $first to the array

Manipulation

Gather together corresponding elements from multiple lists

Given several lists, gather together the first element from every list, the second element from every list, and so on for all corresponding index values in the lists. E.g. for these three lists, first = ['Bruce', 'Tommy Lee', 'Bruce'], last = ['Willis', 'Jones', 'Lee'], years = [1955, 1946, 1940] the result should produce 3 actors. The middle actor should be Tommy Lee Jones.

ruby

first = ['Bruce', 'Tommy Lee', 'Bruce']; last = ['Willis', 'Jones', 'Lee']; years = [1955, 1946, 1940]

result = first.zip(last, years)

java

String[] first = new String[]{"Bruce", "Tommy Lee", "Bruce"};
String[] last = new String[]{"Willis", "Jones", "Lee"};
String[] years = new String[]{"1955", "1946", "1940"};

List<String[]> list = new ArrayList<String[]>(); list.add(first); list.add(last); list.add(years);

String[] result = zip(",", list);

perl

my @first = ('Bruce', 'Tommy Lee', 'Bruce');
my @last = ('Willis', 'Jones', 'Lee');
my @years = (1955, 1946, 1940);

my @actors;

my $max = scalar @first;
for my $index (0 .. $max) {
push @actors, [ $first[$index], $last[$index], $years[$index] ];
};

groovy

first = ['Bruce', 'Tommy Lee', 'Bruce']
last = ['Willis', 'Jones', 'Lee']
years = [1955, 1946, 1940]
actors = [first, last, years].transpose()
assert actors.size() == 3
assert actors[1] == ['Tommy Lee', 'Jones', 1946]

scala

def zip3(l1 : List[_], l2 : List[_],l3 : List[_]) : List[Tuple3[_, _, _]] =
{
def zip3$ (l1$ : List[_], l2$ : List[_], l3$ : List[_], acc : List[Tuple3[_, _, _]]) : List[Tuple3[_, _, _]] = l1$ match
{
case Nil => acc reverse
case l1$head :: l1$tail => zip3$(l1$tail, l2$.tail, l3$.tail, Tuple3(l1$head, l2$.head, l3$.head) :: acc)
}

zip3$(l1, l2, l3, List[Tuple3[_,_,_]]())
}

// ------

val result = zip3(first, last, years)

python

first = ['Bruce', 'Tommy Lee', 'Bruce']
last = ['Willis', 'Jones', 'Lee']
years = [1955, 1946, 1940]

actors = zip(first, last, years)

assert len(actors) == 3
assert actors[1] == ('Tommy Lee', 'Jones', 1946)

cpp

array<String^>^ first = {"Bruce", "Tommy Lee", "Bruce"}; array<String^>^ last = {"Willis", "Jones", "Lee"}; array<String^>^ years = {"1955", "1946", "1940"};

array<String^>^ result = zip<String^>(",", first, last, years);

fsharp

let result = (List.zip3 first last years)

erlang

First = ['Bruce', 'Tommy Lee', 'Bruce'], Last = ['Willis', 'Jones', 'Lee'], Years = [1955, 1946, 1940],

Result = lists:zip3(First, Last, Years),

php

for ($i = 0; $i < $count; $i++) {
$list[] = array($first[$i], $last[$i], $years[$i]);
}

List Combinations

Given two source lists (or sets), generate a list (or set) of all the pairs derived by combining elements from the individual lists (sets). E.g. given suites = ['H', 'D', 'C', 'S'] and faces = ['2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A'], generate the deck of 52 cards, confirm the deck size and check it contains an expected card, say 'Ace of Hearts'.

ruby

suites.each {|s| faces.each {|f| cards << [s, f]}}
puts "Deck %s \'Ace of Hearts\'" % if cards.include?(['h', 'A']) then "contains" else "does not contain" end

java

SortedSet<AbstractMap.SimpleImmutableEntry<String, String> > cards =
new TreeSet<AbstractMap.SimpleImmutableEntry<String, String> >(new CardComparator());

for (String suite : suites)
for (String face : faces)
cards.add(new AbstractMap.SimpleImmutableEntry<String, String>(suite, face));

Boolean containsEntry = cards.contains(new AbstractMap.SimpleImmutableEntry<String, String>("h", "A"));

if (containsEntry) System.out.println("Deck contains 'Ace of Hearts'");
else System.out.println("'Ace of Hearts' not in deck");

perl

@suites = qw(H D C S);
@faces = qw(2 3 4 5 6 7 8 9 10 J Q K A);
@deck = map { $suite=$_; map $suite.$_, @faces; } @suites;
print 'checking deck size: ' . (@deck == 52 ? 'pass' : 'fail') . "\n";
print 'deck contains "Ace of Hearts": ' . (grep(/^HA$/, @deck) ? 'true' : 'false') . "\n";

groovy

faces = ['2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A']
suites = ['H', 'D', 'C', 'S']
deck = [faces, suites].combinations()
assert deck.size() == 52
assert ['A', 'H'] in deck

scala

def product(set1 : List[_], set2 : List[_]) : List[Pair[_, _]] =
{
val p = new mutable.ArrayBuffer[Pair[_, _]]()
for (e1 <- set1) for (e2 <- set2) p += Pair(e1, e2)
p.toList
}

// ------

val cards = product(suites, faces)

printf("Deck has %d cards\n", cards.length)
if (cards.contains(Pair("h", "A"))) println("Deck contains 'Ace of Hearts'")
else println("'Ace of Hearts' not in this deck")

python

suites = ('H', 'D', 'C', 'S')
faces = ('2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A')
deck = [(face,suite) for suite in suites for face in faces]
assert len(deck) == 52
assert ('A', 'H') in deck

cpp

Specialized::StringCollection^ cards = gcnew Specialized::StringCollection;

for each(String^ suite in suites)
for each(String^ face in faces)
cards->Add(makeCard(suite, face));

Console::WriteLine("Deck has {0} cards", cards.Count);
if (cards->Contains(makeCard("h", "A"))) Console::WriteLine("Deck contains 'Ace of hearts'"); else Console::WriteLine("'Ace of hearts' not in deck");

fsharp

let cards = (List.fold_left (fun acc suite -> acc @ (List.map (fun face -> (suite, face)) faces)) [] suites)

printfn "Deck has %d cards" (List.length cards)
printfn "%s" (if (List.exists (fun e -> e = ("h", "A")) cards) then "Deck contains 'Ace of Hearts'" ; else "'Ace of Hearts' not in deck")

let product (set1 : List<'a>) (set2 : List<'a>) : List<'a * 'a> =
let p = new ResizeArray<'a * 'a>()
for e1 in set1 do for e2 in set2 do p.Add(e1, e2) done done
Array.to_list (p.ToArray())

// ------

let cards = product suites faces

printfn "Deck has %d cards" (List.length cards)
printfn "%s" (if (List.exists (fun e -> e = ("h", "A")) cards) then "Deck contains 'Ace of Hearts'" ; else "'Ace of Hearts' not in deck")

erlang

Cards = lists:foldl(fun (Suite, Acc) -> Acc ++ lists:flatmap(fun (Face) -> [{Suite, Face}] end, Faces) end, [], Suites),

io:format("Deck has ~B cards~n", [length(Cards)]),
IsMember = lists:member({h, 'A'}, Cards),
io:format("~s~n", [if IsMember -> "Deck contains 'Ace of Hearts'" ; true -> "'Ace of Hearts' not in deck" end]),

Cards = sofs:to_external(sofs:product(sofs:set(Suites), sofs:set(Faces))),

io:format("Deck has ~B cards~n", [length(Cards)]),
IsMember = lists:member({h, 'A'}, Cards),
io:format("~s~n", [if IsMember -> "Deck contains 'Ace of Hearts'" ; true -> "'Ace of Hearts' not in deck" end]),

Deck2 = [{S, V} || S <- [d, c, h, s], V <- [2, 3, 4, 5, 6, 7, 8, 9, 10, 'J', 'Q', 'K', 'A']],
52 = length(Deck2),
true = lists:member({h, 'A'}, Deck2).

csharp

using System;
using System.Collections.Generic;
using System.Linq;

namespace Combinations
{
class Program
{
public static void Main(string[] args)
{
// Define the given lists
// Since List`1 implements the interface IEnumerable`1, this can easily be redefined as List`1.
IEnumerable<string> suites = new string[] { "H", "D", "C", "S" };
IEnumerable<string> faces = new string[] { "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A" };

// LINQ Query to perform a Cartesian product and create an anonymous type to hold the results.
// "var" is required to define this as an IEnumerable`1
var deck =
from suite in suites // For each suite in suites
from face in faces // Match it with a face in face.
select new
{
Suite = suite,
Face = face
};

// Verify the count (uses LINQ extension)
if (deck.Count() == 52)
{
Console.WriteLine("Count matches!");
}

// Verify that the Ace of Hearts is in the deck (uses LINQ extension)
if (deck.Contains(new {Suite = "H", Face = "A"}))
{
Console.WriteLine("Ace of Hearts found!");
}

// Example of how to iterate through the list.
// "var" here is required since we are using an anonymous type
foreach(var card in deck)
{
Console.WriteLine("Suite: {0} Face: {1}", card.Suite, card.Face);
}

// If you desire to work with a List`1, you can convert this to a normal list at any time:
Console.WriteLine("\nConverting to list!");
var list = deck.ToList();
Console.WriteLine("Suite: {0} Face: {1}", list[5].Suite, list[5].Face);
Console.WriteLine("List count: {0}", list.Count); // 52

Console.ReadLine();
}
}
}

php

foreach ($suites as $suite) {
foreach ($faces as $face) {
$cards[] = $suite.$face;
}
}
if (count($cards) == 52) {
echo "The deck have all 52 cards.\n";
}
if (in_array("HA", $cards)) {
echo "The deck contains 'Ace of Heart'\n";
} else {
echo "The deck doesn't contain 'Ace of Heart'\n";
}

Perform an operation on every item of a list

Perform an operation on every item of a list, e.g.
for the list ["ox", "cat", "deer", "whale"] calculate
the list of sizes of the strings, e.g. [2, 3, 4, 5]

ruby

["ox", "cat", "deer", "whale"].map{|i| i.length}

java

public class SolutionXX {
public static void main(String[] args) {
String[] list = {"ox", "cat", "deer", "whale"};
for (String str : list) {
System.out.println(str.length() + " ");
}
}
}

perl

my @list = qw{ox cat deer whale};

my @lengths = map {length($_)} @list;

print "@list\n";
print "@lengths\n";

groovy

animals = ["ox", "cat", "deer", "whale"]
assert animals*.size() == [2, 3, 4, 5]

scala

val sizes = List("ox", "cat", "deer", "whale") map {_ size}
assert(sizes == List(2, 3, 4, 5))

python

print map(lambda x: len(x), ["ox", "cat", "deer", "whale"])

print [len(x) for x in ['ox', 'cat', 'deer', 'whale']]

cpp

std::list<std::string> data;
data.push_back("ox");
data.push_back("cat");
data.push_back("deer");
data.push_back("whale");

std::list<std::size_t> result;
for (std::list<std::string>::const_iterator iter = data.begin(), iter_end = data.end(); iter != iter_end; ++iter){
result.push_back( iter->length());
}

for (std::list<std::size_t>::const_iterator iter = result.begin(), iter_end = result.end(); iter != iter_end; ++iter){
std::cout << *iter << " ";
}
return 0;

fsharp

let lengths = List.map String.length ["ox"; "cat"; "deer"; "whale"]

erlang

lists:map(fun (X) ->length(X) end, List).

ocaml

List.map String.length ["ox"; "cat"; "deer"; "whale"];;

csharp

using System.Collections.Generic;
public class OperationOnEach {
public static void Main() {
var list = new List<string>() { "ox", "cat", "deer", "whale" };
list.ForEach( System.Console.WriteLine );
}
}

php

$sizes = array_map('strlen', array('ox', 'cat', 'deer', 'whale'));

Split a list of things into numbers and non-numbers

Given a list that might contain e.g. a string, an integer, a float and a date,
split the list into numbers and non-numbers.

ruby

now=Time.now
things=["hello", 25, 3.14, now]

numbers=things.select{|i| i.is_a? Numeric}
others=things-numbers

java

public class NumbersSolution {
public static void main(String[] args) {
List<Object> items = Arrays.asList(new Object[] { new Date(), 12L, 15.4, 99, "x" } ) ;
List<Object> numbers = new ArrayList<Object>() ;
List<Object> nonNumbers = new ArrayList<Object>() ;
for (Object item : items )
(item instanceof Number ? numbers : nonNumbers).add(item) ;
}
}

public class NumbersSolution {
public static void main() {
List<Object> numbers = new ArrayList<Object>() ;
List<Object> nonNumbers = new ArrayList<Object>() ;
for (Object item : new Object[] { new Date(), 12L, 15.4, 99, "x" } )
(item instanceof Number ? numbers : nonNumbers).add(item) ;
}
}

perl

use Scalar::Util qw(looks_like_number);
my @things = ('hello',25,3.14,scalar(localtime(time)));
my @numbers;
my @others;
for ( @things ) {
if ( looks_like_number $_ ) {
push @numbers, $_;
} else {
push @other, $_;
}
}

groovy

now = new Date()
things = ["hello", 25, 3.14, now]
(numbers, others) = things.split{ it instanceof Number }
assert numbers == [25, 3.14]
assert others == ["hello", now]

scala

val now = new java.util.Date()
val result = List("hello", 25, 3.14, now) partition { _.isInstanceOf[Number] }
assert(result == (List(25, 3.14), List("hello", now)))

python

import re
data = '34234aff340980adf0e0fa0fefl' ## or ''.join(array)

nonDigits = re.findall(re.compile('\D'), data)
digits = re.findall(re.compile('\d'), data)

fsharp

erlang

% Wrapped call to the auxiliary function
number_split(Xs) ->
number_split(Xs, [], []).

% The auxiliary function
number_split([], Num, NonNum) ->
{Num, NonNum};
number_split([X|Xs], Num, NonNum) ->
case is_number(X) of
true ->
number_split(Xs, [X|Num], NonNum);
false ->
number_split(Xs, Num, [X|NonNum])
end.

List = ["hello", 25, 3.14, calendar:local_time()],
{Numbers, NonNumbers} = lists:partition(fun(E) -> is_number(E) end, List)

csharp

using System;
using System.Collections.Generic;
using System.Linq;

// AFAIK, there just isn't a good way to do this in C#
public class ListSplitter {
public static bool IsNumeric(object o) {
var d = new Decimal();
return decimal.TryParse(o.ToString(), out d);
}
public static void Main() {
var list = new List<object>() { "foo", DateTime.Now, 1, "bar", 2.4 };

// the Where method does the work...
var numbers = list.Where( el => IsNumeric(el) );
var nonNumbers = list.Where( el => ! IsNumeric(el) );
}

}

php

$now = new DateTime();
$things = array('hello', 25, 3.14, $now);
$numbers = array_filter($things, 'is_numeric');
$others = array();
foreach ($things as $thing) {
if (!in_array($thing, $numbers)) {
$others[] = $thing;
}
}

Maps

Declaration

Define an empty map

ruby

map = []

java

Map map = new HashMap();

perl

%map = {}

groovy

def map = [:]

Map map = new HashMap();

scala

val map = mutable.Map.empty

val map = mutable.HashMap.empty[String, Int]

python

map = {}

cpp

Hashtable^ hash = gcnew Hashtable;

Generic::Dictionary<String^, String^>^ dict = gcnew Generic::Dictionary<String^, String^>();

std::map<int, std::string> m;

fsharp

let map = Map.empty

let map = new Generic.Dictionary<string, string>()

let map = new Hashtable()

erlang

Map = dict:new(),

Map = orddict:new(),

Map = gb_trees:empty(),

Map = ets:new(the_map_name, [set, private, {keypos, 1}]),

php

$map = array();

$map = array("" => "");

Define an unmodifiable empty map

ruby

map = [].freeze

java

Map empty = Collections.EMPTY_MAP;

SortedMap empty = MapUtils.EMPTY_SORTED_MAP;

perl

# perl does not provide unmodifiable maps/hashes, but you could use "constant
# functions", if you really need them

sub MAP () { {} }

groovy

empty = Collections.EMPTY_MAP

map = [:].asImmutable()

def empty = MapUtils.EMPTY_SORTED_MAP

def empty = ImmutableMap.of()

scala

val map = immutable.Map.empty

val map = immutable.TreeMap.empty[String, Int]

python

import collections
EmptyDict = collections.namedtuple("EmptyDict", "")
e = EmptyDict()

fsharp

// Most native fsharp data structures are immutable - updating a 'map' sees a modified copy created
let map = Map.empty

erlang

% Erlang data structures are immutable - updating a 'map' sees a modified copy created
Map = dict:new(),

php

/* It's not possible to define an array as a constant
* Instead we can use the serialize-function */

$fruits = array("apple", "banana", "orange");
define("FRUITS", serialize($fruits));
echo FRUITS; // a:3:{i:0;s:5:"apple";i:1;s:6:"banana";i:2;s:6:"orange";}
$my_fruits = unserialize(FRUITS); // and normal array again

Define an initial map

Define the map {circle:1, triangle:3, square:4}

ruby

shapes = {'circle'=>1, 'triangle'=>3, 'square'=>4}

shapes = Hash['circle', 1, 'triangle', 3, 'square', 4]

java

Map shapes = new HashMap();
shapes.put("circle", 1);
shapes.put("triangle", 3);
shapes.put("square", 4);

Map shapes = new HashMap() {{ put("circle",1); put("triangle",3); put("square",4); }}

perl

%map = (circle => 1, triangle => 3, square => 4);

groovy

shapes = [circle:1, triangle:3, square:4]

// if you require a specific type of map ...
LinkedHashMap shapes1 = [circle:1, triangle:3, square:4]
Properties shapes2 = [circle:1, triangle:3, square:4]
TreeMap shapes3 = [circle:1, triangle:3, square:4]
shapes4 = [circle:1, triangle:3, square:4] as ConcurrentHashMap // as variation

scala

val shapes = immutable.TreeMap("circle" -> 1, "triangle" -> 3, "square" -> 4)

val shapes = mutable.Map.empty[String, Int]

shapes += "circle" -> 1
shapes += "triangle" -> 3
shapes += "square" -> 4

var shapes = immutable.Map.empty[String, Int]

shapes = shapes + ("circle" -> 1)
shapes = shapes + ("triangle" -> 3)
shapes = shapes + ("square" -> 4)

python

shapes = {'circle': 1, 'square': 4, 'triangle': 2}

cpp

Hashtable^ shapes = gcnew Hashtable;

shapes->Add("circle", 1);
shapes->Add("triangle", 3);
shapes->Add("square", 4);

Generic::Dictionary<String^, int>^ shapes = gcnew Generic::Dictionary<String^, int>();

shapes->Add("circle", 1);
shapes->Add("triangle", 3);
shapes->Add("square", 4);

fsharp

let shapes = Map.of_list [("circle", 1); ("triangle", 3); ("square", 4)]

let shapes = Map.empty.Add("circle", 1).Add("triangle", 3).Add("square", 4)

let shapes = new Generic.Dictionary<string, int>()
shapes.Add("circle", 1)
shapes.Add("triangle", 3)
shapes.Add("square", 4)

erlang

Map = dict:from_list([{circle, 1}, {triangle, 3}, {square, 4}]),

Map0 = dict:new(),

% Erlang variables are 'single-assignment' i.e. they cannot be reassigned
Map1 = dict:store(circle, 1, Map0),
Map2 = dict:store(triangle, 3, Map1),
Map3 = dict:store(square, 4, Map2),

Map0 = gb_trees:empty(),

Map1 = gb_trees:enter(circle, 1, Map0),
Map2 = gb_trees:enter(triangle, 3, Map1),
Map3 = gb_trees:enter(square, 4, Map2),

Map = gb_trees:from_orddict(lists:keysort(1, [{circle, 1}, {triangle, 3}, {square, 4}])),

Map = ets:new(the_map_name, [ordered_set, private, {keypos, 1}]),
ets:insert(Map, [{circle, 1}, {triangle, 3}, {square, 4}]),

php

$map = array("circle" => 1, "triangle" => 3, "square" => 4);

Access

Check if a key exists in a map

Given a map pets {joe:cat,mary:turtle,bill:canary} print "ok" if an pet exists for "mary"

ruby

puts "ok" if map.has_key?('mary')

puts "ok" if map['mary'] # Only works if map entry can't be nil or false

java

if (pets.containsKey("mary")) System.out.println("ok");

perl

%pets = (joe => 'cat', mary => 'turtle', bill => 'canary');
print 'ok' if ($pets{'mary'});

groovy

pets = [joe:'cat', mary:'turtle', bill:'canary']
if(pets.containsKey('mary')) println 'ok'

pets = [joe:'cat', mary:'turtle', bill:'canary']
if(pets.mary) println 'ok'

scala

if (pets.contains("mary")) println("ok")

python

pets = dict(joe='cat', mary='turtle', bill='canary')
if ("mary" in pets) print "ok"

cpp

if (pets->ContainsKey("mary")) Console::WriteLine("ok");

if (pets.find("mary") != pets.end()){
std::cout << "ok" << std::endl;
}

fsharp

if (Map.mem "mary" pets) then printfn "ok"

if pets.ContainsKey("mary") then printfn "ok"

erlang

dict:is_key(mary, Pets) andalso begin io:format("ok~n"), true end.

IsMember = ets:member(Pets, mary), if (IsMember) -> io:format("ok~n") ; true -> false end.

case gb_trees:lookup(mary, Pets) of none -> false ; _ -> io:format("ok~n") end.

php

if (array_key_exists("mary", $pets)) {
echo "ok";
}

if (isset($pets["mary"])) { // only works if $pets["mary"] can't be false or 0
echo "ok";
}

Retrieve a value from a map

Given a map pets {joe:cat,mary:turtle,bill:canary} print the pet for "joe" ("cat")

ruby

puts map['joe']

java

String pet = pets.get("joe");

perl

%pets = (joe => 'cat', mary => 'turtle', bill=>'canary');
print $pets{joe};

groovy

pets = [joe:'cat', mary:'turtle', bill:'canary']
assert pets['joe'] == 'cat'

assert pets.joe == 'cat'

scala

if (pets.contains("joe")) println(pets("joe"))

println(pets.getOrElse("joe", "*** no pet owned ***"))

python

print pets['joe']

cpp

if (pets->ContainsKey("joe")) Console::WriteLine(pets["joe"]);

fsharp

if (Map.mem "joe" pets) then printfn "%s" (Map.find "joe" pets)

if (pets |> Map.exists (fun key _ -> key = "joe")) then printfn "%s" (Map.find "joe" pets)

let key = "joe"
match (pets |> Map.tryfind key) with
| Some(value) -> printfn "%s" value
| None -> printfn "Key %s not found" key

if pets.ContainsKey("joe") then printfn "%s" pets.["joe"]

if pets.ContainsKey("joe") then printfn "%s" (pets.["joe"] :?> string)

erlang

dict:is_key(joe, Pets) andalso begin io:format("~w~n", [dict:fetch(joe, Pets)]), true end.

case dict:find(joe, Pets) of error -> false ; {ok, Pet} -> io:format("~w~n", [Pet]) end.

IsMember = ets:member(Pets, joe), if (IsMember) -> io:format("~w~n", [ets:lookup_element(Pets, joe, 2)]) ; true -> false end.

case ets:match(Pets, {joe, '$1'}) of [] -> false ; [[Pet]] -> io:format("~w~n", [Pet]) end.

case gb_trees:lookup(joe, Pets) of none -> false ; {value, Pet} -> io:format("~w~n", [Pet]) end.

php

echo $pets["joe"];

Add an entry to a map

Given an empty pets map, add the mapping from "rob" to "dog"

ruby

pets['rob']='dog'

java

pets.put("rob", "dog");

perl

$pets{rob} = 'dog';

groovy

pets['rob'] = 'dog'

pets.rob = 'dog'

pets.put('rob', 'dog')

scala

pets += "rob" -> "dog"

python

pets['rob'] = 'dog'

cpp

pets->Add("rob", "dog");

pets["rob"] = "dog";

fsharp

pets <- (Map.add "rob" "dog" pets)

pets.Add("rob", "dog")

erlang

Pets1 = dict:store(rob, dog, Pets0).

ets:insert(Pets, {rob, dog}).

Pets1 = gb_trees:enter(rob, dog, Pets0).

php

$pets["rob"] = "dog";

Remove an entry from a map

Given a map pets {joe:cat,mary:turtle,bill:canary} remove the mapping for "bill" and print "canary"

ruby

puts map['bill']

java

System.out.println(pets.remove("bill"))

perl

print delete $pets{bill};

groovy

pets = [joe:'cat', mary:'turtle', bill:'canary']
println pets.remove('bill')

scala

val pet = pets("bill") ; pets -= "bill" ; println(pet)

println(pets.removeKey("bill") match { case Some(pet) => pet ; case None => "***" })

python

print pets.pop('bill')

cpp

if (pets->ContainsKey("bill"))
{
String^ value = safe_cast<String^>(pets["bill"]); pets->Remove("bill");
Console::WriteLine("{0}", value);
}

fsharp

let key = "bill"
match (pets |> Map.tryfind key) with
| Some(value) -> pets <- (Map.remove key pets) ; printfn "%s : %s removed" key value
| None -> printfn "Key %s not found" key

let key = "bill"
let entry = if (pets.ContainsKey(key)) then Some(pets.[key]) ; else None
pets.Remove(key)

match entry with
| Some(value) -> printfn "%s" value
| None -> printfn "key not found"

erlang

Pet = dict:fetch(bill, Pets0), Pets1 = dict:erase(bill, Pets0), io:format("~w~n", [Pet]),

Pet = ets:lookup_element(Pets, bill, 2), ets:delete(Pets, bill), io:format("~w~n", [Pet]),

{value, Pet} = gb_trees:lookup(bill, Pets0), Pets1 = gb_trees:delete(bill, Pets0), io:format("~w~n", [Pet]),

php

$last = array_pop($pets); // removes last key and assign it to the variable
echo $last;

$last = $pets[count($pets)-1];
echo $last;
unset($last);

$bill = $pets["bill"];
echo $bill;
unset($bill);

Algorithms

Create a histogram map from a list

Given the list [a,b,a,c,b,b], produce a map {a:2, b:3, c:1} which contains the count of each unique item in the list

ruby

histogram = {}
list.each { |item| histogram[item] = (histogram[item] || 0) +1 }

java

Map map = new HashMap();
for (Iterator it = list.iterator(); it.hasNext();) {
String s = (String) it.next();
if (!map.containsKey(s)) {
map.put(s, new Integer(1));
} else {
map.put(s, new Integer(((Integer)map.get(s)).intValue() + 1));
}
}

LinkedMap histogram = new LinkedMap();

for (Object letter : list)
histogram.put(letter, !histogram.containsKey(letter) ? 1 : MapUtils.getIntValue(histogram, letter) + 1);

perl

foreach(@list) {
$histogram{$_}++;
}

groovy

histogram = [:]
list.each { item ->
if (!histogram.containsKey(item)) histogram[item] = 0
histogram[item]++
}

histogram = [:]
list.each { histogram[it] = (histogram[it] ?: 0) + 1 }

scala

list foreach { (x) => histogram += x -> (histogram.getOrElse(x, 0) + 1) }

val data = List("a", "b", "a", "c", "b", "b")
val keys = data removeDuplicates
val hist = Map.empty[String, Int] ++ keys.map{ k => (k, (data count (_==k)))}
assert(hist == Map("a"->2, "b"->3, "c"->1))

python

from collections import defaultdict
h = defaultdict(int)
for k in "abacbb":
h[k] += 1

cpp

for each(String^ entry in input) hash[entry] = hash->ContainsKey(entry)
? Convert::ToInt32(hash[entry]->ToString()) + 1 : 1;

for each(String^ entry in input) dict[entry] = dict->ContainsKey(entry) ? dict[entry] + 1 : 1;

fsharp

let histogram = (List.fold_left (fun (acc : Map<char, int>) (e : char) -> if (Map.mem e acc) then (Map.add e ((Map.find e acc) + 1) acc) ; else (Map.add e 1 acc)) (Map.empty) list)

let histogram list =
let rec histogram' list' dict' =
match list' with
| [] -> dict'
| x :: xs ->
match Map.tryfind x dict' with
| Some(Value) -> histogram' xs (Map.add x (Value + 1) dict')
| None -> histogram' xs (Map.add x 1 dict')
histogram' list Map.empty

// ------

let histogram' = histogram list

let histogram = (List.fold_left (fun (acc : Generic.Dictionary<char, int>) (e : char) -> (if acc.ContainsKey(e) then acc.[e] <- acc.[e] + 1 ; else acc.Add(e, 1)) ; acc) (new Generic.Dictionary<char, int>()) list)

erlang

% Imperative Solution
Histogram = histogram(List),

% Functional (1) Solution
Histogram = histogram(List),

csharp

using System.Collections.Generic;
using System.Linq;

// This is a "functional" C# approach

// NOTE: In C# "maps" are of type Dictionary<Tkey, TValue>
// so our histogram map is of type Dictionary<object, int>
public class HistogramMap {
public Dictionary<object, int> FromList(List<object> list) {
// The "Aggregate" method works like "inject" in many other languages.
return list.Aggregate(
new Dictionary<object, int>(),
(map, obj) => {
// If this is the first time we've seen this obj, set the count to 0
if (!map.ContainsKey(obj)) map[obj] = 0;

// Increment the count
map[obj]++;

// Return the map for the next iteration.
// NOTE: This does NOT return from our "FromList" method
return map;
}
);
}

public static void Main() {
// Create our Histogram Map from a new list
var map = new HistogramMap().FromList(
new List<object>() { 'a', 'b', 'a', 'c', 'b', 'b' }
);

// This just prints the result
System.Console.WriteLine (
string.Join (", ",
// "Select" works like "map" or "collect" in many other languages
map.Select( kvp =>
string.Format("{0} : {1}", kvp.Key, kvp.Value)
).ToArray()
)
);
}
}

php

$list = array("a","b","a","c","b","b");
$map = array_count_values($list);

Categorise a list

Given the list [one, two, three, four, five] produce a map {3:[one, two], 4:[four, five], 5:[three]} which sorts elements into map entries based on their length

ruby

lengths = {}
list.each do |x|
len = x.size
lengths[len] = (lengths[len] || [])
lengths[len] << x
end

java

SortedMap<Integer, List<String> > map = new TreeMap<Integer, List<String> >(); int key; List<String> vlist;

for (String item : list)
{
key = item.length(); vlist = map.containsKey(key) ? map.get(key) : new ArrayList<String>();
vlist.add(item); map.put(key, vlist);
}

MultiValueMap map = new MultiValueMap();
for (Object item : list) map.put(((String) item).length(), item);

perl

@list = qw(one two three four five);
push @{$map{length($_)}}, $_ for (@list);

groovy

map = ['one', 'two', 'three', 'four', 'five'].groupBy{ it.size() }

scala

list foreach { (x) => map += x.length -> (x :: map.getOrElse(x.length, Nil)) }

list foreach { (x) => map += x.length -> (map.getOrElse(x.length, Nil) ::: List(x)) }

List("one", "two", "three", "four", "five") groupBy (_ size)

python

c = defaultdict(list)
for k in ["one", "two", "four", "three", "five"]:
c[len(k)].append(k)

cpp

for each(String^ entry in input)
{
key = entry->Length;
if (!hash->ContainsKey(key)) hash[key] = gcnew ArrayList;
safe_cast<ArrayList^>(hash[key])->Add(entry);
}

fsharp

let catmap = (List.fold_left (fun (acc : Map<int, List<string> >) (e : string) -> if (Map.mem e.Length acc) then (Map.add e.Length ((Map.find e.Length acc) @ [e]) acc) ; else (Map.add e.Length [e] acc)) (Map.empty) list)

erlang

% Imperative Solution
CatList = categorise(List),

% Functional (1) Solution
CatList = categorise(List),

csharp

using System.Collections.Generic;
using System.Linq;
public class ListCategorizer {
public static void Main() {
var list = new List<string>() { "one", "two", "three", "four", "five" };
var categories = list.GroupBy(el => el.Length)
.ToDictionary( g => g.Key, // key
g => g.ToList() ); // value
}
}

php

foreach ($array as $m) {
$l = strlen($m);
$map[$l][] = $m;
}
arsort($map);

Structure

Conditionals

Perform an action if a condition is true (IF .. THEN)

Given a variable name, if the value is "Bob", display the string "Hello, Bob!". Perform no action if the name is not equal.

ruby

if (name=='Bob')
puts "Hello, Bob!"
end

puts "Hello, Bob!" if name=='Bob'

java

if (name.equals("Bob")) {
System.out.println("Hello, Bob!");
}

perl

if ($name eq "Bob") {
print "Hello, Bob!"
}

groovy

if (name=='Bob')
println "Hello, Bob!"

scala

val name = "Bob"
if (name.equals("Bob")) printf("Hello, %s!\n", name)

val name = "Bob"

// Scala supports operator overloading, so the following works correctly
if (name == "Bob") printf("Hello, %s!\n", name)

python

if name == 'Bob':
print 'Hello, Bob!'

cpp

if (name == "Bob") Console::WriteLine("Hello, {0}!", name);

if (name == "Bob") std::cout << "Hello, " << name << "!" << std::endl;

fsharp

if name = "Bob" then printfn "Hello, %s!" name

name = "Bob" && begin printfn "Hello, %s!" name ; true end

erlang

if (Name == "Bob") -> io:format("Hello, ~s!~n", [Name]) ; true -> false end.

case Name of "Bob" -> io:format("Hello, ~s!~n", [Name]) ; _ -> false end.

Name == "Bob" andalso (begin io:format("Hello, ~s!~n", [Name]), true end).

ocaml

if name = "Bob"
then print_string "Hello, Bob!"
else ()

php

if($name == "Bob") {
echo "Hello, Bob!";
}

Perform different actions depending on a boolean condition (IF .. THEN .. ELSE)

Given a variable age, if the value is greater than 42 display "You are old", otherwise display "You are young"

ruby

if (age > 42)
puts "You are old"
else
puts "You are young"
end

puts (age>42) ? "You are old" : "You are young"

java

if (age > 42) {
System.out.println("You are old");
} else {
System.out.println("You are young");
}

System.out.println("You are " + ((age>42)?"old":"young"));

perl

if ($age > 42) {
print "You are old"
}
else {
print "You are young"
}

groovy

if (age > 42)
println "You are old"
else
println "You are young"

println "You are " + (age > 42 ? "old" : "young")

scala

val age = 42
if (age > 42) println("You are old") else println("You are young")

python

if age > 42:
print 'You are old'
else:
print 'You are young'

print age > 42 and 'You are old' or 'You are young'

cpp

if (age > 42) Console::WriteLine("You are old");
else Console::WriteLine("You are young");

Console::WriteLine("You are {0}", (age > 42 ? "old" : "young"));

std::printf("You are %s\n", (age > 42 ? "old" : "young"));

fsharp

if age > 42 then printfn "You are old" else printfn "You are young"

let message = if age > 42 then "old" else "young"
printfn "You are %s" message

erlang

if Age > 42 -> io:format("You are old~n") ; true -> io:format("You are young~n") end.

Message = if Age > 42 -> "old" ; true -> "young" end, io:format("You are ~s~n", [Message]).

case Age > 42 of true -> io:format("You are old~n") ; false -> io:format("You are young~n") end.

case Age of _ when Age > 42 -> io:format("You are old~n") ; _ -> io:format("You are young~n") end.

Message = case Age of _ when Age > 42 -> "old" ; _ -> "young" end, io:format("You are ~s~n", [Message]).

Age > 42 andalso (begin io:format("You are old~n"), true end) orelse (begin io:format("You are young~n"), true end).

ocaml

if age = 42
then print_string "Youre are old"
else print_string "You are young"

csharp

int age = 41;

if (age > 42)

System.Console.WriteLine("You are old");
else
System.Console.WriteLine("You are young");

php

if($age < 42) {
echo "You are young";
} else {
echo "You are old";
}

echo "You are " . (($age < 43) ? "young" : "old");

Perform different actions depending on several boolean conditions (IF .. THEN .. ELSIF .. ELSE)

ruby

if age > 84
puts "You are really ancient"
elsif age > 30
puts "You are middle-aged"
else
puts "You are young"
end

java

if (age > 84) System.out.println("You are really ancient");
else if (age > 30) System.out.println("You are middle-aged");
else System.out.println("You are young");

perl

if ($age > 84) {
print "You are really ancient";
} elsif ($age > 30) {
print "You are middle-aged";
} else {
print "You are young";
}

groovy

if (age > 84)
println "You are really ancient"
else if (age > 30)
println "You are middle-aged"
else
println "You are young"

scala

val age = 65

if (age > 84) println("You are really ancient")
else if (age > 30) println("You are middle-aged")
else println("You are young")

python

if age > 84:
print 'You are really ancient'
elif age > 30:
print 'You are middle-aged'
else:
print 'You are young'

cpp

if (age > 84) Console::WriteLine("You are really ancient");
else if (age > 30) Console::WriteLine("You are middle-aged");
else Console::WriteLine("You are young");

Console::WriteLine("You are {0}", (age > 84 ? "really ancient" : age > 30 ? "middle-aged" : "young"));

std::cout << "You are " << (age > 84 ? "really ancient" : age > 30 ? "middle-aged" : "young") << std::endl;

fsharp

if age > 84 then printfn "You are really ancient"
elif age > 30 then printfn "You are middle-aged"
else printfn "You are young"

let message = match age with
| _ when age > 84 -> "really ancient"
| _ when age > 30 -> "middle-aged"
| _ -> "young"
printfn "You are %s" message

erlang

if
Age > 84 -> io:format("You are really ancient~n");
Age > 30 -> io:format("You are middle-aged~n");
true -> io:format("You are young~n")
end.

case Age of
_ when Age > 84 -> io:format("You are really ancient~n");
_ when Age > 30 -> io:format("You are middle-aged~n");
true -> io:format("You are young~n")
end.

php

echo "You are " . (($age > 84) ? "really ancient" : (($age > 30) ? "middle-aged" : "young"));

$response = "You are ";
if ($age > 84) {
$response .= "really ancient";
} else if ($age > 30) {
$response .= "middle-aged";
} else {
$response .= "young";
}
echo $response;

Replacing a conditional with many branches with a switch/case statement

Many languages support more compact forms of branching than just if ... then ... else such as switch or case or match. Use such a form to add an appropriate placing suffix to the numbers 1..40, e.g. 1st, 2nd, 3rd, 4th, ..., 11th, 12th, ... 39th, 40th

ruby

def suffixed(number)
last_digit = number.to_s[-1..-1].to_i
suffix = case last_digit
when 1 then 'st'
when 2 then 'nd'
when 3 then 'rd'
else 'th'
end
suffix = 'th' if (11..13).include?(number)
"#{number}#{suffix}"
end

(1..40).each {|n| puts suffixed(n) }

java

String[] array = new String[40];
for(int n = 1; n <= array.length; n++)
array[n-1] = Integer.toString(n);
for(int n = 0; n < array.length; n++)
{
int y = Integer.parseInt(array[n]);
if(array[n].length() > 1)
y = Integer.parseInt(array[n].substring(1));
switch(y)
{
case 1: {array[n] += "st"; break;}
case 2: {array[n] += "nd"; break;}
case 3: {array[n] += "rd"; break;}
default: array[n] += "th";
}
}

perl

sub suffix {
my $n = shift;

return 'th' if $n % 100 >= 4 && $n % 100 <= 20;
return 'st' if $n % 10 == 1;
return 'nd' if $n % 10 == 2;
return 'rd' if $n % 10 == 3;
return 'th';

}

foreach my $n (1..40) {
print $n.suffix($n)."\n";
}

groovy

def suffix(n) {
switch(n) {
case { n % 100 in 4..20 } : return 'th'
case { n % 10 == 1 } : return 'st'
case { n % 10 == 2 } : return 'nd'
case { n % 10 == 3 } : return 'rd'
default : return 'th'
}
}
(1..40).each { n ->
println "$n${suffix(n)}"
}

scala

object FourToTwenties {
def unapply (n: Int) = (4 to 20).contains(n % 100)
}

def suffix (n: Int) = {
n match {
case FourToTwenties() => "th"
case n if n % 10 == 1 => "st"
case n if n % 10 == 2 => "nd"
case n if n % 10 == 3 => "rd"
case _ => "th"
}
}

for (n <- 1 to 40) {
println(n.toString + suffix(n))
}

python

def affix(num):
num = num == 1 and str(num) + 'st' or num == 2 and str(num) + 'nd' or \
num == 3 and str(num) +'rd' or str(num) + 'th'
return num

print [affix(x) for x in xrange(1,41)]

cpp

#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int num,i,x;
cout<<"Enter the range:";
cin>>num;
for(i=1;i<=num;i++)
{
x=i%10;
switch(i)
{
case 11:
case 12:
case 13:cout<<i<<"th ";
continue;
}
switch(x)
{
case 1: cout<<i<<"st ";break;
case 2: cout<<i<<"nd ";break;
case 3: cout<<i<<"rd ";break;
default: cout<<i<<"th ";
}
}
getch();
}

fsharp

let suffix = function
| n when n > 10 && n < 20 -> "th"
| n when n % 10 = 1 -> "st"
| n when n % 10 = 2 -> "nd"
| n when n % 10 = 3 -> "rd"
| _ -> "th"

seq { 1 .. 40 }
|> Seq.iter (fun n -> printfn "%i%s" n (suffix n))

erlang

Suffix = case Num of
N when N > 10, N < 20 -> "th";
N when N rem 10 =:= 1 -> "st";
N when N rem 10 =:= 2 -> "nd";
N when N rem 10 =:= 3 -> "rd";
_ -> "th"
end,
io_lib:format("~w~s", [Num, Suffix])

php

Loops

Perform an action multiple times based on a boolean condition, checked before the first action (WHILE .. DO)

Starting with a variable x=1, Print the sequence "1,2,4,8,16,32,64,128," by doubling x and checking that x is less than 150.

ruby

x=1
while x < 150
puts x
x *=2
end

java

int x = 1;
while (x < 150) {
System.out.println(x+",");
x*=2;
}

perl

my $x = 1;
while($x < 150) {
print $x, ",";
$x *=2
}

groovy

x = 1
while (x < 150) {
print x + ","
x *= 2
}
println()

scala

var x = 1 ; while (x < 150) { printf("%d,", x) ; x *= 2 }

python

x = 1
while x < 150:
print '%s, ' % x,
x *= 2

cpp

int x = 1;

while (x < 150) { x *= 2; Console::Write("{0},", x); }
Console::WriteLine();

for (int x = 1; x < 150; x *= 2) { std::cout << x << ","; }
std::cout << std::endl;

fsharp

let mutable x = 1
while x < 150 do printf "%d, " x ; (x <- x * 2) done

erlang

X = 1, print_while_X_less_150(X).

Pred = fun (X) -> X < 150 end,
Action = fun (X) -> io:format("~B,", [X]), X * 2 end,
X = 1,

while_do(Pred, Action, X).

php

$x = 1;
while($x < 150) {
echo "$x,";
$x *= 2;
}

$x = 0;
$c = pow(2, $x);
while($c < 150) {
echo "$c,";
$c = pow(2, $x++);
}

Perform an action multiple times based on a boolean condition, checked after the first action (DO .. WHILE)

Simulate rolling a die until you get a six. Produce random numbers, printing them until a six is rolled. An example output might be "4,2,1,2,6"

ruby

# Ruby has no DO..WHILE construct. Need to write it as a WHILE
rnd = 0
while (rnd != 6)
rnd = rand(6)+1
print rnd
print "," if (rnd!=6)
end

java

int rnd;
do {
rnd = (int)(Math.random()*6)+1;
System.out.print(rnd);
if (rnd!=6) {
System.out.print(",");
}
} while(rnd!=6);

perl

do {
my $number = int(rand(6)+1);
print $number;
print ',' if ($number != 6);
} while ($number != 6);

groovy

// Groovy has no do..while; use a normal while
int dice = 0
while (dice != 6) {
dice = Math.random() * 6 + 1
print dice
if (dice != 6) print ','
}

scala

val dice = new GenRandInt(1, 6) ; var rnd = 0 ; var fmt = ""
do { rnd = dice.next ; fmt = if (rnd != 6) "%d," else "%d" ; printf(fmt, rnd) } while (rnd != 6)

python

import random, itertools

def dice():
while True:
yield random.randint(1,6)

print ", ".join(str(d) for d in itertools.takewhile(lambda x: x < 6, dice()))

cpp

Random^ rnd = gcnew Random;

int dice = rnd->Next(1, 7); Console::Write("{0}", dice);
do { Console::Write(",{0}", (dice = rnd->Next(1, 7))); } while (dice != 6);
Console::WriteLine();

fsharp

open System
let rand = Random()

Seq.initInfinite (fun _ -> rand.Next(1, 7))
|> Seq.takeWhile (fun x -> x < 6)
|> fun items -> String.Join(",", items)
|> function s when s = "" -> printfn "6" | s -> printfn "%s,6" s

erlang

Pred = fun (DiceRoll) -> DiceRoll =/= 6 end,
Action = fun (DiceRoll) -> io:format("~B,", [DiceRoll]), dice_roll() end,

do_while(Pred, Action, dice_roll()).

-module(dice).
-export([start/0]).

start() ->
roll(dice_roll()).

roll(6) ->
io:format("6~n", []);
roll(N) ->
io:format("~B,", [N]),
roll(dice_roll()).

dice_roll() -> random:uniform(6).

php

do {
$rand = rand(1,6);
echo $rand;
if ($rand != 6) echo ", ";
} while ($rand != 6);

Perform an action a fixed number of times (FOR)

Display the string "Hello" five times like "HelloHelloHelloHelloHello"

ruby

puts "Hello"*5

5.times { print "Hello" }

java

for(int i=0;i<5;i++) {
System.out.print("Hello");
}

perl

print "Hello" x 5

print "Hello" for (1..5)

groovy

println "Hello" * 5

5.times { print "Hello" }; println()

scala

// Using overloaded '*' operator (String-specific)
print("Hello" * 5)

List.range(0, 5) foreach { (_) => print("Hello") }

for (_ <- List.range(0, 5)) print("Hello")

// Lazy version
for (_ <- Stream.range(0, 5)) print("Hello")

dotimes(5, _ => print("Hello"))

(0 until 5) foreach { (_) => print("Hello") }

5 times { print("Hello") }

python

print "Hello" * 5

cpp

for(int i = 0; i < 5; ++i) Console::Write("Hello");

for(int i = 5; i > 0; --i) Console::Write("Hello");

dotimes(5, hello);

fsharp

for i = 1 to 5 do printf "Hello" done

dotimes 5 (fun () -> printf "Hello")

// Repetition via ranging over a List type(index ignored)
for _ in list do printf "Hello" done

// Repetition via ranging over a Sequence type(index ignored)
for _ in sequence do printf "Hello" done

// Repetition via ranging over an Array type(index ignored)
for _ in array do printf "Hello" done

erlang

dotimes(5, fun () -> io:format("Hello") end).

lists:foreach(fun (_) -> io:format("Hello") end, lists:seq(1, 5)).

ocaml

let rec write_hello = function
0 -> ()
| 1 ->
print_string "Hello" ;
write_hello (n-1)
;;
write_hello 5;;

php

for($i = 0; $i < 5; $i++) {
echo "Hello";
}

Perform an action a fixed number of times with a counter

Display the string "10 .. 9 .. 8 .. 7 .. 6 .. 5 .. 4 .. 3 .. 2 .. 1 .. Liftoff!"

ruby

10.downto(1) { |n| print n, " .. " }
puts "Liftoff!"

java

for(int i=10; i>=1; i--) {
System.out.print(i + " .. ");
}
System.out.print("Liftoff!");

perl

for (my $i = 10; $i > 0; $i--) {
print "$i .. ";
}
print "Liftoff!";

groovy

10.downto(1) { print it + " .. " }
println "Liftoff!"

scala

for (i <- List.range(1, 11).reverse) printf("%d .. ", i) ; println("Liftoff!")

for (i <- List.range(-10, 0)) printf("%d .. ", (-i)) ; println("Liftoff!")

var i = 10 ; while (i > 0) { printf("%d .. ", i) ; i -= 1 } ; println("Liftoff!")

for (i <- -10 to -1) printf("%d .. ", (-i)) ; println("Liftoff!")

python

print " .. ".join(str(i) for i in range(10, 0, -1)), ".. liftoff!"

cpp

for(int i = 10; i != 0; --i) Console::Write("{0} .. ", i);
Console::WriteLine("Liftoff!");

fsharp

for i = 10 downto 1 do printf "%d .. " i done
printfn "Liftoff!"

// Repetition via ranging over a Sequence type
for i in {10 .. -1 .. 1} do printf "%d .. " i done ; printfn "Liftoff!"

erlang

fromto(10, 1, -1, fun (X) -> io:format("~B .. ", [X]) end), io:format("Liftoff!~n").

lists:foreach(fun (X) -> io:format("~B .. ", [X]) end, lists:seq(10, 1, -1)), io:format("Liftoff!~n").

php

for($i = 10; $i > 0; $i--) {
echo $i." .. ";
}
echo "Liftoff!";

Files

Reading

Read the contents of a file into a string

ruby

file = File.new("Solution108.rb")
whole_file = file.read

java

String text = FileUtils.readFileToString(new File("Solution109.java"), "UTF-8");

RandomAccessFile raf = null; byte[] buffer; String text = null;

try
{
raf = new RandomAccessFile("Solution399.java", "r");
buffer = new byte[(int)raf.length()]; raf.read(buffer);
text = new String(buffer);
}

perl

@file = read()

open(my $fh, '<', $path) or die "can't open $path: $!";
$string = do { local $/; <$fh> };
close $fh;

groovy

contents = file.text

scala

val text = FileUtils.readFileToString(new File("Solution467.scala"))

val text = Source.fromFile("Solution1256.scala") mkString("")

python

contents = open('myFile.txt', 'rt').read()

cpp

IO::FileStream^ file; String^ buffer;

try
{
file = gcnew IO::FileStream("test.txt", IO::FileMode::Open);
buffer = gcnew String((gcnew IO::BinaryReader(file))->ReadChars(file->Length));
}

IO::StreamReader^ stream; String^ buffer;

try
{
stream = gcnew IO::StreamReader("test.txt");
buffer = stream->ReadToEnd();
}

String^ buffer = IO::File::ReadAllText("test.txt");

fsharp

let file = new FileStream("test.txt", FileMode.Open)
let buffer = new String((new BinaryReader(file)).ReadChars(Convert.ToInt32(file.Length)))

let stream = new StreamReader("test.txt")
let buffer = stream.ReadToEnd()

let buffer = File.ReadAllText("test.txt")

erlang

Text = readfile("Solution607.erl"),

Text = readfile("Solution608.erl"),

php

$file_contents = file_get_contents("file.txt");

Process a file one line at a time

Open the source file to your solution and print each line in the file, prefixed by the line number, like:
1> First line of file
2> Second line of file
3> Third line of file

ruby

File.open("Solution103.rb").each_with_index { |line, count|
puts "#{count} > #{line}
}

java

BufferedReader br = null;
try {
br = new BufferedReader(new FileReader("Solution104.java"));
String line = null;
int lineNumber = 1;
while ((line=br.readLine())!=null) {
System.out.println(lineNumber + "> " + line);
lineNumber++;
}
} catch (IOException e) {
throw new RuntimeException(e);
} finally {
if (br!=null) {
try {
br.close();
} catch (Exception e) {
// ok
}
}
}

LineNumberReader lnr = null; PrintWriter pw = null; String line;

try
{
lnr = new LineNumberReader(new FileReader("Solution400.java"));
pw = new PrintWriter(System.out);
while ((line = lnr.readLine()) != null) pw.printf("%d> %s\n", lnr.getLineNumber(), line);
}

perl

open($fh, '<', $path) or die "can't open $path: $!";
$c = 1;
print $c++ . "> $_" for (<$fh>);
close $fh;

groovy

int count = 0
file.eachLine { line ->
println "${++count} > $line"
}

file.eachLine { line, count ->
println "${++count} > $line"
}

scala

val source = Source.fromFile(new File("Solution468.scala")).getLines
var n = 1 ; while (source.hasNext) { printf("%d> %s", n, source.next) ; n += 1 }

val source = Source.fromFile(new File("Solution469.scala")).getLines
for ((line, n) <- source zipWithIndex) { printf("%d> %s", (n + 1), line) }

python

for no, line in enumerate(open(__file__)):
print "%d> %s" % (no+1, line.rstrip())

cpp

IO::StreamReader^ stream; String^ ln; int i = 0;

try
{
stream = gcnew IO::StreamReader("test.txt");
while ((ln = stream->ReadLine())) Console::WriteLine("{0}> {1}", ++i, ln);
}

int i = 0;
for each(String^ line in IO::File::ReadAllLines("test.txt")) Console::WriteLine("{0}> {1}", ++i, line);

fsharp

let stream = new StreamReader("test.txt")
let mutable i = 1
let mutable line = stream.ReadLine()
while (line <> null) do printfn "%d> %s" i line ; line <- stream.ReadLine() ; i <- i + 1 done
stream.Close()

let proc_a_line (filename : string) proc =
let stream = new StreamReader(filename)
let rec proc_a_line' count line =
match line with
| null -> stream.Close()
| _ -> proc count line ; proc_a_line' (count + 1) (stream.ReadLine())
proc_a_line' 1 (stream.ReadLine())

// ------

let _ = proc_a_line "test.txt" (fun i line -> printfn "%d> %s" i line)

let reader(filename : string) = seq {
use sr = new StreamReader(filename)
while not sr.EndOfStream do
let line = sr.ReadLine()
yield line
done
}

// ------

reader("test.txt") |> Seq.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

File.ReadAllLines("test.txt") |> Array.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

// Unlike ReadAllLines, ReadLines (new in .NET 4) only reads the file
// one line at a time, rather than reading the entire file into an array first.

open System.IO
File.ReadLines("test.txt") |> Seq.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

erlang

Reader = fun (IODevice) -> io:get_line(IODevice, "") end,
Worker = fun (Line, N) -> io:format("~B> ~s", [N, Line]), N + 1 end,

while_not_eof("Solution609.erl", Reader, Worker, 1).

Reader = fun (Filename) -> {ok, Contents} = file:read_file(Filename), Contents end,
Transformer = fun (Line, N) -> string:concat(string:concat(integer_to_list(N), "> "), Line) end,
Printer = fun (Line) -> io:format("~s~n", [Line]) end,

Lines = string:tokens(binary_to_list(Reader("Solution610.erl")), "\n"),
NewLines = lists:zipwith(Transformer, Lines, lists:seq(1, length(Lines))),
lists:foreach(Printer, NewLines).

php

$lines = file('file.txt');
foreach ($lines as $lnum => $line) {
echo $line_num."> ".$line; // you may want to add a <br />\n
}

<?php
$lines = new SplFileObject('file.txt');
foreach ($lines as $line) {
echo $line;
}
?>

Writing

Write a string to a file

ruby

File.new("a_file", "w") << "some text"

java

FileWriter fw = null;

try
{
fw = new FileWriter("test.txt");
fw.write("This line overwites file contents!");
}

PrintWriter pw = null;

try
{
pw = new PrintWriter(new BufferedWriter(new FileWriter("test.txt")));
pw.print("This line overwites file contents!");
}

perl

open($fh, '>', $path) or die "can't open $path: $!";
print $fh "This line overwites file contents!";
close $fh;

groovy

file.delete()
file << 'some text'

file.text = 'some text'

scala

FileUtils.writeStringToFile(new File("test.txt"), "This line overwites file contents!")

val fw = new FileWriter("test.txt") ; fw.write("This line overwites file contents!") ; fw.close()

python

open('test.txt', 'wt').write('Hello World!')

cpp

IO::StreamWriter^ stream;

try
{
stream = gcnew IO::StreamWriter("test.txt", false);
stream->WriteLine("This line overwites file contents!");
}

fsharp

let stream = new StreamWriter("test.txt", false)
stream.WriteLine("This line overwrites file contents!")

erlang

Line = "This line overwites file contents!\n",
{ok, IODevice} = file:open("test.txt", [write]), file:write(IODevice, Line), file:close(IODevice).

php

/****
* For some (security)reason I couldn't
* submit this without adding a space to
* the functionnames. Please remove it :)
****/

if ($fh = f open("file.txt", 'w')) {
f write($fh, "Some text\n");
f close($fh);
}

<?php
file_put_contents('file.txt', 'a string');
?>

Append to a file

ruby

file = File.new('/tmp/test.txt', 'a+') ; file.puts 'This line appended to file!!' ; file.close()

java

FileWriter fw = null;

try
{
fw = new FileWriter("test.txt", true);
fw.write("This line appended to file!");
}

PrintWriter pw = null;

try
{
pw = new PrintWriter(new BufferedWriter(new FileWriter("test.txt", true)));
pw.print("This line appended to file!");
}

perl

open($fh, '>>', $path) or die "can't open $path: $!";
print $fh "This line is appended to the file!";
close $fh;

groovy

file << 'some text'

scala

val fw = new FileWriter("test.txt", true) ; fw.write("This line appended to file!") ; fw.close()

python

open('test.txt', 'at').write('Hello World!\n')

cpp

IO::StreamWriter^ stream;

try
{
stream = gcnew IO::StreamWriter("test.txt", true);
stream->WriteLine("This line appended to file!");
}

fsharp

let stream = new StreamWriter("test.txt", true)
stream.WriteLine("This line appended to file!")

erlang

Line = "This line appended to file!\n",
{ok, IODevice} = file:open("test.txt", [append]), file:write(IODevice, Line), file:close(IODevice).

php

/****
* For some (security)reason I couldn't
* submit this without adding a space to
* the functionnames. Please remove it :)
****/

if ($fh = f open("file.txt", 'a')) { // a == append
f write($fh, "Append some text\n");
f close($fh);
}

<?php
file_put_contents('file.txt', 'a string to append', FILE_APPEND);
?>

Directories

Process each file in a directory

ruby

directory = '/tmp' ; Dir.foreach(directory) {|file| puts "#{file}"}

java

for (File file : (new File("c:\\")).listFiles()) process(file);

perl

use File::Glob;

for (<*>) {
process_file($_) if (-f);
}

groovy

dir.eachFile{ f -> process(f) }

scala

for (file <- new File("c:\\").listFiles) { processFile(file) }

python

import os
results = (process(f) for f in os.listdir(".") if os.path.isfile(f))

cpp

for each(String^ filename in IO::Directory::GetFiles(dirname)) process(filename);

fsharp

let dirname = "c:\\"

let processFile filename = printfn "%s" filename
for filename in Directory.GetFiles(dirname) do processFile filename done

let dirname = "c:\\"

Directory.GetFiles(dirname) |> Array.iter (fun filename -> printfn "%s" filename)

erlang

% File basenames only - many tasks require absolute paths to work
lists:foreach(fun (FileOrDirPath) -> Worker(FileOrDirPath) end, file:list_dir(Directory)).

% Absolute paths provided - will accomodate most tasks
lists:foreach(fun (FileOrDirPath) -> Worker(FileOrDirPath) end, list_dir_path(Directory)).

php

if ($dh = opendir($dir)) { // if we have access
while (($file = readdir($dh)) !== false) { // as long as there is a file
echo "name: $file\n"; // echo its name
}
closedir($dh); // close the dir
}

Process each file in a directory recursively

ruby

def procdir(dirname)
Dir.foreach(dirname) do |dir|
dirpath = dirname + '/' + dir
if File.directory?(dirpath) then
if dir != '.' && dir != '..' then
puts "DIRECTORY: #{dirpath}" ; procdir(dirpath)
end
else
puts "FILE: #{dirpath}"
end
end
end

# ------

procdir('/tmp')

java

processDirectory(new File("c:\\"));

perl

use File::Glob;

process_directory(".");

sub process_directory {
my $dir = shift;
for my $file (<$dir/*>) {
next unless (-r $file);
if (-f $file) {
process_file($file);
} elsif (-d $file) {
process_directory($file);
}
}
}

groovy

dir.eachFileRecurse{ f -> process(f) }

scala

processDirectory(new File("c:\\"))

python

import os
results = (process(os.path.join(p, n)) for p,d,l in os.walk(".") for n in l)

cpp

void processFile(String^ filename) { Console::WriteLine("{0}", filename); }

void processDirectory(String^ dirname)
{
for each(String^ filename in IO::Directory::GetFiles(dirname)) processFile(filename);
for each(String^ subdirname in IO::Directory::GetDirectories(dirname)) processDirectory(subdirname);
}

int main()
{
processDirectory("c:\\");
}

fsharp

let processDirectory dirname proc =
let rec processDirectory' dirname' =
Directory.GetFiles(dirname') |> Array.iter proc
Directory.GetDirectories(dirname') |> Array.iter processDirectory'
processDirectory' dirname

// ------

let dirname = "c:\\"

processDirectory dirname (fun filename -> printfn "%s" filename)

erlang

filelib:fold_files(Directory, ".*", true, fun (FileOrDirPath, Acc) -> Worker(FileOrDirPath), Acc end, []).

process_dir(Directory, Worker).

php

if ($dir_handle = opendir($dir))
list_dir($dir_handle);

function list_dir($dh) {
// as long as we can read the dir
while (($file = readdir($dh)) !== false) {
// if it's a dir and it's not the current dir nor the above dir
if (is_dir($file) && $file != '.' && $file !='..') {
// open the dir, print it's name and all files inside
$handle = opendir($file);
echo $file."\n";
list_dir($handle);
// if it's a simple file
} else if ($file != '.' && $file !='..') {
// type it's name
echo $file."\n";
}
}
closedir($dir_handle); // close the dirs
}

Dates

Parsing

Parse a date and time from a string

Given the string "2008-05-06 13:29", parse it as a date representing 6th March, 2008 1:29:00pm in the local time zone.

ruby

# With timezone info
puts Time.parse('2008-05-06 13:29')

java

DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm");
Date date = df.parse("2008-05-06 13:29");

DateTimeFormatter fmt = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm");
DateTime dt = fmt.parseDateTime("2008-05-06 13:29");

perl

#! /usr/bin/perl
# -*- Mode: CPerl -*-

use strict;
use POSIX;

# Given the string "2008-05-06 13:29", parse it as a date
# representing 6th March, 2008 1:29:00pm in the local time zone.

my $ds = "2008-05-06 13:29";

my $y;
my $m;
my $d;
my $hr;
my $mn;

print "Original: ",$ds,"\n";

if ( $ds =~ /(\d{4})-(\d{2})-(\d{2})\s+(\d{2}):(\d{2})/ ){
$y = $1 - 1900;
$m = $2;
$d = $3;
$hr = $4;
$mn = $5;

printf "Nominal: %s\n",
strftime("%e %B, %Y %l:%M:%S%P",0, $mn , $hr, $d, $m,$y);

my $eth = "";
if ( $d == 1 ){
$eth = "st";
} elsif ( $d == 2 ){
$eth = "nd";
} elsif ( $d == 3 ){
$eth = "rd";
} else {
$eth = "th";
}

printf "As required: %d%s %s\n",$d,$eth,
strftime("%B, %Y %l:%M:%S%P",0, $mn , $hr, $d, $m,$y);
}

#eos

groovy

def date = new SimpleDateFormat("yyy-MM-dd HH:mm").parse("2008-05-06 13:29")

def date = Date.parse("yyy-MM-dd HH:mm", "2008-05-06 13:29")

scala

val date = new SimpleDateFormat("yyy-MM-dd HH:mm").parse("2008-05-06 13:29")

python

import time
time.strptime("2008-05-06 13:29", "%Y-%m-%d %H:%M")

cpp

DateTimeOffset^ dateTime = DateTimeOffset::Parse("2008-05-06 13:29");

// Use format specifiers to appropriately format string
// 1. Default culture
Console::WriteLine("{0}", dateTime->ToString("d MMMM, yyyy h:mm:sstt"));

// 2. Nominated culture
Console::WriteLine("{0}", dateTime->ToString("d MMMM, yyyy h:mm:sstt"), Globalization::CultureInfo::CreateSpecificCulture("en-us"));

DateTimeOffset^ dateTime = DateTimeOffset::Parse("2008-05-06 13:29");

// Customize date/time string
Text::StringBuilder^ dsb = gcnew Text::StringBuilder(40);
dsb->Append(dateTime->ToString("%d"))->Append("th ")->Append(dateTime->ToString("MMMM, yyyy h:mm:ss"))->Append(dateTime->ToString("tt")->ToLower());

Console::WriteLine("{0}", dsb);

fsharp

let dateTime = DateTimeOffset.Parse("2008-05-06 13:29")

// Use format specifiers to appropriately format string
// 1. Default culture
printfn "%s" (dateTime.ToString("d MMMM, yyyy h:mm:sstt"))

// 2. Nominated culture
Console.WriteLine("{0}", dateTime.ToString("d MMMM, yyyy h:mm:sstt"), Globalization.CultureInfo.CreateSpecificCulture("en-us"))

let dateTime = DateTimeOffset.Parse("2008-05-06 13:29")

// Customize date/time string
let dsb = ((new StringBuilder(40)).Append(dateTime.ToString("%d")).Append("th ").Append(dateTime.ToString("MMMM, yyyy h:mm:ss")).Append(dateTime.ToString("tt").ToLower()))

printfn "%s" (dsb.ToString())

erlang

% AFAIK, no datetime-parsing library exists; 'parse_to_datetime' is a simplistic, problem-specific hack
LocalDateTime = erlang:universaltime_to_localtime(parse_to_datetime("2008-05-06 13:29:34")),

php

echo date("jS F, Y g:i:sa", strtotime("2008-05-06 13:29")); // small version

Printing

Display information about a date

Display the day of month, day of year, month name and day name of the day 8 days from now.

ruby

require 'date'

next_week = Date.today + 8

puts next_week.day # day of month
puts next_week.yday # day of year
puts next_week.strftime('%B') # month name
puts next_week.strftime('%A') # day name

java

Calendar cal = Calendar.getInstance();
cal.add(DAY_OF_YEAR, 8);
System.out.println(cal.get(DAY_OF_MONTH));
System.out.println(cal.get(DAY_OF_YEAR));
System.out.println(new SimpleDateFormat("MMMM").format(cal.getTime()));
System.out.println(new SimpleDateFormat("EEEE").format(cal.getTime()));

perl

#! /usr/bin/perl
# -*- Mode: CPerl -*-

use strict;
use Date::Calc qw(:all);

my $days_in_future = $ARGV[0];
$days_in_future = 8 unless $days_in_future;

my ($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) = Localtime();

my ($fyear,$fmonth,$fday) = Add_Delta_Days($year,$month,$day,$days_in_future);

printf "Now: %d-%2.2d-%2.2d %2.2d:%2.2d:%2.2d\n",
$year,$month,$day,$hour,$min,$sec;

printf "Then: %d-%2.2d-%2.2d %2.2d:%2.2d:%2.2d\n",
$fyear,$fmonth,$fday,$hour,$min,$sec;

printf "Then: day of month: %d\n",$fday;
printf "Then: day of year: %d\n",Day_of_Year($fyear,$fmonth,$fday);
printf "Then: day of name: %s\n",
Day_of_Week_to_Text(Day_of_Week($fyear,$fmonth,$fday));
printf "Then: month name: %s\n",Month_to_Text($fmonth);

#eos

groovy

use (TimeCategory) {
eight_days_time = 1.week.from.now + 1.day
}
println eight_days_time[DAY_OF_MONTH]
println eight_days_time.format('d') // alternative to above
println eight_days_time[DAY_OF_YEAR]
println eight_days_time.format('MMMM')
println eight_days_time.format('EEEE')

scala

import java.util.Calendar
import java.text.SimpleDateFormat

val formatString = "d, D, MMMM, EEEE"
val cal = Calendar.getInstance

cal.add(Calendar.DAY_OF_YEAR, 8)

println(new SimpleDateFormat(formatString) format cal.getTime)

python

from datetime import datetime, timedelta

eightDaysFromNow = datetime.now() + timedelta(days=8)

print eightDaysFromNow.strftime('%d') # day of month
print eightDaysFromNow.strftime('%j') # day of year
print eightDaysFromNow.strftime('%B') # month name FULL
print eightDaysFromNow.strftime('%A') # day of week name FULL

fsharp

Using F# interactive

> let Then = DateTime.Now.AddDays(8.0)
- let dayNumber = Then.DayOfYear.ToString()
- let solution = Then.ToString("dd " + dayNumber + " MMMM dddd");;

val Then : DateTime = 08/08/2010 08:58:05
val dayNumber : string = "220"
val solution : string = "08 220 August Sunday"

>

php

$eightdays = strtotime("+8 days");

$dayofmonth = date("d", $eightdays); // 3
$dayofyear = date("z", $eightdays); // 183
$monthname = date("F", $eightdays); // July
$dayname = date("l", $eightdays); // Saturday

$eightdays = time() + 1 * 60 * 60 * 24 * 8;

$dayofmonth = date("d", $eightdays); // 3
$dayofyear = date("z", $eightdays); // 183
$monthname = date("F", $eightdays); // July
$dayname = date("l", $eightdays); // Saturday

Display a date in different locales

Display a language/locale friendly version of New Year's Day for 2009 for several languages/locales. E.g. for languages English, French, German, Italian, Dutch the output might be something like:

Thursday, January 1, 2009
jeudi 1 janvier 2009
giovedì 1 gennaio 2009
Donnerstag, 1. Januar 2009
donderdag 1 januari 2009

(Indicate in comments where possible if any language specific or operating system configuration needs to be in place.)

java

Calendar cal = Calendar.getInstance();
cal.set(2009, Calendar.JANUARY, 1);
Locale[] locales = { ENGLISH, FRENCH, ITALIAN, GERMAN, new Locale("nl") };

for (Locale l : locales) {
System.out.println(getDateInstance(FULL, l).format(cal.getTime()));
}

perl

#!/usr/bin/perl
use warnings;
use strict;

use locale;
use POSIX qw(strftime);
use Time::Local;

my $date=timegm(0,0,0, 1,0,101); #00:00:00 01/01/2001

my $str_time = strftime "%c", gmtime;

print "Date: $str_time\n";

groovy

cal = Calendar.instance
cal.set(2009, JANUARY, 1)
[ENGLISH, FRENCH, ITALIAN, GERMAN, new Locale('nl')].each { lang ->
println getDateInstance(FULL, lang).format(cal.time)
}

// relies on Java I18N capabilities which supports many locales, see:
// http://java.sun.com/javase/technologies/core/basic/intl/
// available Locales may depend on your version of Java and/or
// operating system and/or installed fonts

scala

val date = new GregorianCalendar(2009, JANUARY, 1).getTime
val locales = List(ENGLISH, FRENCH, ITALIAN, GERMAN, new Locale("nl"))
println(locales.map{getDateInstance(FULL, _).format(date)}.mkString("\n"))

python

from datetime import datetime
from locale import setlocale, LC_TIME

now = datetime(2009, 1, 1)

locales = ('en_us', 'fr_fr', 'it_it', 'de_de', 'nl_nl')
for locale in locales:
setlocale(LC_TIME, locale)
print now.strftime('%A, %B %d %Y')

fsharp

open System
open System.Globalization

let jan1 = DateTime(2009, 1, 1)

[ "en-US"; "fr-FR"; "de-DE"; "it-IT"; "nl-NL" ]
|> List.map CultureInfo.CreateSpecificCulture
|> List.map (fun c -> jan1.ToString("D", c))
|> List.iter (printfn "%s")

php

/* Be aware of that you need to have the locales installed */
setlocale(LC_TIME, "en_US");
echo strftime("%A, %B %e, %Y%n"); // %n = \n in strftime()
setlocale(LC_TIME, "fr_FR"); // French
echo strftime("%A, %B %e, %Y%n");
setlocale(LC_TIME, "de_DE"); // German
echo strftime("%A, %B %e, %Y%n");
setlocale(LC_TIME, "it_IT"); // Italian
echo strftime("%A, %B %e, %Y%n");
setlocale(LC_TIME, "nl_NL", "nld_nld"); // Dutch; Unix and Windows
echo strftime("%A, %B %e, %Y%n");

$locales = array("en_US", "fr_FR", "de_DE", "nl_NL", "it_IT");
foreach ($locales as $locale) {
setlocale(LC_TIME, $locale);
echo strftime("%A, %B %d %Y%n");
}

Creation

Display the current date and time

Create a Date object representing the current date and time. Print it out.
If you can also do this without creating a Date object you can show that too.

ruby

puts DateTime.now

java

import java.util.Date;

public class SolutionXX {
public static void main(String[] args) {
Date now = new Date();
System.out.println(now.toString());
}
}

perl

use Class::Date;
my $date = Class::Date->now();
print $date->string()."\n";

print localtime()."\n";

groovy

println new Date()

scala

println(new java.util.Date)

python

from datetime import datetime
print datetime.utcnow()

fsharp

printfn "%A" System.DateTime.Now

erlang

io:format("~p~n", [calendar:local_time()])

php

echo date('r') . "\n";
$d = new DateTime();
echo $d->format('r') . "\n";

OOP

Basics

Define a class

Declare a class named Greeter that takes a string on creation and greets using this string if you call the "greet" method.

ruby

class Greeter
def initialize(whom) @whom = whom end
def greet() puts "Hello, #{@whom}!" end
end

(Greeter.new("world")).greet()

java

class Greeter
{
public Greeter(String whom) { this.whom = whom; }
public void greet() { System.out.printf("Hello, %s\n", whom); }
private String whom;
}

public class Solution381 {
public static void main(String[] args) {
(new Greeter("world")).greet();
}
}

perl

{ package Greeter;
sub new {
my $self = {};
my $type = shift;
$self->{'whom'} = shift;
bless $self, $type;
}

sub greet {
my $self = shift;
print "Hello " . $self->{'whom'} . "!\n";
}
}

my $greeter = Greeter->new("world");
$greeter->greet();

groovy

// version using named parameters
class Greeter {
def whom
def greet() { println "Hello, $whom" }
}
new Greeter(whom:'world').greet()

// version using traditional constructor
class Greeter {
private whom
Greeter(whom) { this.whom = whom }
def greet() { println "Hello, $whom" }
}
new Greeter('world').greet()

scala

class Greeter(whom : String) { def greet() = { printf("Hello %s\n", whom) } }

(new Greeter("world!")).greet()

python

class Greeter(object):
""" Greet someone.
"""
def __init__(self, whom):
self._whom = whom
def greet(self):
print "Hello, %s!" % self._whom

Greeter("world").greet()

cpp

class Greeter
{
public:
Greeter(const std::string& whom);
void greet() const;

private:
std::string whom;
};

int main()
{
Greeter* gp = new Greeter("world");
gp->greet();
delete gp;
}

Greeter::Greeter(const std::string& whom) : whom(whom) {}

void Greeter::greet() const
{
std::cout << "Hello, " << whom << std::endl;
}

public ref class Greeter
{
public:
Greeter(String^ whom);
void greet();

private:
initonly String^ whom;
};

int main()
{
(gcnew Greeter(L"world"))->greet();
}

Greeter::Greeter(String^ whom) : whom(whom) {}

void Greeter::greet()
{
Console::WriteLine(L"Hello, {0}", whom);
}

fsharp

type Greeter(whom' : string) =
member this.greet() = printfn "Hello, %s!" whom'

(new Greeter("world")).greet()

type Greeter(whom' : string) =
let whom : string = whom'
member this.greet() = printfn "Hello, %s!" whom

(new Greeter("world")).greet()

type Greeter =
class
val whom : string
new(whom') = { whom = whom' }
member this.greet() = printfn "Hello, %s!" this.whom
end

(new Greeter("world")).greet()

erlang

Greeter = make_greeter("world!"),
Greeter(greet).

csharp

using System;

class Greeter
{
private string name {get;set;}

public void Greet(){
Console.WriteLine("Hello, {0}",name);
}

public Greeter(string name){
this.name = name;
}
}

class Test
{
static void Main()
{
new Greeter("Dante").Greet();
}
}

php

class Greeter {
private $whom;
public function __construct($whom) {
$this->whom = $whom;
}
public function greet() {
echo "Hello $this->whom.";
}
}
$g = new Greeter("Giacomo Girolamo");
$g->greet();

Instantiate object with mutable state

Reimplement the Greeter class so that the 'whom' property or data member remains private but is mutable, and is provided with getter and setter methods. Invoke the setter to change the greetee, invoke 'greet', then use the getter in displaying the line, "I have just greeted {whom}.".

For example, if the greetee is changed to 'Tommy' using the setter, the 'greet' method would display:

Hello, Tommy!

The getter would then be used to display the line:

I have just greeted Tommy.

ruby

class Greeter
attr_accessor :whom
def initialize(whom) @whom = whom end
def greet() puts "Hello, #{@whom}!" end
end

greeter = Greeter.new("world") ; greeter.greet()

greeter.whom = 'Tommy' ; greeter.greet()
puts "I have just greeted %s" % greeter.whom

java

class Greeter {
private String whom;

public Greeter(String whom) {
this.whom = whom;
}

public String getWhom() {
return whom;
}

public void setWhom(String whom) {
this.whom = whom;
}

public void greet() {
System.out.println("Hello " + whom + "!");
}
}
Greeter greeter = new Greeter("World");
greeter.greet();
greeter.setWhom("Tommy");
greeter.greet();
System.out.println("I have just greeted " + greeter.getWhom() + ".");

perl

package Greeter;
sub new {
my ($class, $whom) = @_;
bless {whom => $whom}, $class;
}
sub whom {
my ($self, $whom) = @_;
if ($whom) { $self->{whom} = $whom; }
else { return $self->{whom} }
}
sub greet {
my ($self) = @_;
my $whom = $self->{whom};
print "Hello, $whom!\n";
}
package main;

my $g = new Greeter ("world");
$g->greet;

$g->whom("Tommy");
$g->greet;
print "I have just greeted " . $g->whom . "\n";

groovy

class Greeter {
def whom
def greet() { println "Hello, $whom!" }
}

greeter = new Greeter(whom:"world"); greeter.greet()

greeter.whom = 'Tommy'; greeter.greet()
println "I have just greeted $greeter.whom"

scala

class Greeter(var whom: String) {
def greet() = println("Hello " + whom + "!")
}

// Is this really a private value with getter and setter methods,
// or just a public mutable value?

val greeter = new Greeter("World")
greeter.greet()
greeter.whom = "Tommy"
greeter.greet()
printf("I have just greeted %s.\n", greeter.whom)

python

class Greeter(object):
_whom = None

def __init__(self, whom):
self._whom = whom

@property
def whom(self):
return self._whom

@propset(whom)
def whom(self, value=None):
self._whom = value

def greet(self):
print 'Helo, %s!' % self._whom

greeter = Greeter('Winston')
greeter.greet()
greeter.whom = 'Tommy'
greeter.greet()

# required for Python 2.5 or less
def propset(prop):
assert isinstance(prop, property)
def helper(func):
return property(prop.fget, func, prop.fdel, prop.__doc__)
return helper

class Greeter(object):
_whom = None

def __init__(self, whom):
self._whom = whom

@property
def whom(self):
return self._whom

@propset(whom)
def whom(self, value=None):
self._whom = value

def greet(self):
print 'Helo, %s!' % self._whom

greeter = Greeter('Winston')
greeter.greet()
greeter.whom = 'Tommy'
greeter.greet()

fsharp

type Greeter(name:string) =
let mutable whom = name

member this.Whom
with get () = whom
and set v = whom <- v

member this.Greet() =
printfn "Hello, %s!" whom

let greeter = Greeter("World")
greeter.Greet()
greeter.Whom <- "Tommy"
greeter.Greet()
printfn "I have just greeted %s." greeter.Whom

csharp

class Greeter
{
public string Name {get;set;}

public void Greet(){
Console.WriteLine("Hello, {0}",Name);
}

public Greeter(string name){
this.Name = name;
}

// Driver
public static void Main()
{
var g = new Greeter("Dante");

g.Name = "Tommy";
g.Greet();
Console.Write("I have just greated {0}", g.Name);
}
}

php

class Greeter {
private $whom;
public function __construct($whom) {
$this->whom = $whom;
}
public function greet() {
echo "Hello $this->whom.\n";
}
public function getWhom() {
return $this->whom;
}
public function setWhom($whom) {
$this->whom = $whom;
}
}
$g = new Greeter("Giacomo Girolamo");
$g->greet();
$g->setWhom("Jean-Jaques");
$g->greet();
echo "I have just greeted " . $g->getWhom() . ".\n";

Inheritance

Implement Inheritance Heirarchy

Implement a Shape abstract class which will form the base of an inheritance hierarchy that models 2D geometric shapes. It will have:

* A non-mutable 'name' property or data member set by derived or descendant classes at construction time
* A 'area' method intended to be overridden by derived or descendant classes ( double precision floating point return value)
* A 'print' method (also for overriding) will display the shape

's name, area, and all shape-specific values



Two derived or descendant classes will be created:

* Circle    -> Constructor requires a '

radius' argument, and a 'circumference

' method to be implemented  

* Rectangle -> Constructor requires '

length' and 'breadth' arguments, and a 'perimeter

' method to be implemented 



Instantiate an object of each class, and invoke each objects '

print' method to show relevant details.

ruby

class Shape
def initialize(name="") @name = name end
end

class Circle < Shape
def initialize(radius) super("circle") ; @radius = radius end

def area() 3.14159 * @radius * @radius end
def circumference() 2 * 3.14159 * @radius end

def print()
puts "I am a #{@name} with ->"
puts "Radius: %.2f" % @radius
puts "Area: %.2f" % self.area()
puts "Circumference: %.2f\n" % self.circumference()
end

end

class Rectangle < Shape
def initialize(length, breadth) super("rectangle") ; @length = length ; @breadth = breadth end

def area() @length * @breadth end
def perimeter() 2 * @length + 2 * @breadth end

def print()
puts "I am a #{@name} with ->"
printf("Length, Width: %.2f, %.2f\n", @length, @breadth)
puts "Area: %.2f" % self.area()
puts "Perimeter: %.2f\n" % self.perimeter()
end
end

# ------

shapes = [Circle.new(4.2), Rectangle.new(2.7, 3.1), Rectangle.new(6.2, 2.6), Circle.new(17.3)]
shapes.each {|shape| shape.print}

java

/*
* Will work with version 1.4 if you remove the @Override annotation
* and declare floating point numbers using the primitive "double"
*/
abstract class Shape {
protected final String name;
public Shape(String name) {
this.name = name;
}
public abstract Double area();
public abstract void print();
}
class Circle extends Shape {
private Double radius;
public Circle(Double radius) {
super("circle");
this.radius = radius;
}
@Override
public Double area() {
return Math.PI * Math.pow(radius, 2);
}
@Override
public void print() {
System.out.println("A " + name + " with radius " + radius
+ ", area " + area() + " and circumference "
+ circumference() + ".");
}
public Double circumference() {
return 2 * Math.PI * radius;
}
}
class Rectangle extends Shape {
private Double length, breadth;
public Rectangle(Double length, Double breadth) {
super("Rectangle");
this.length = length;
this.breadth = breadth;
}
@Override
public Double area() {
return length * breadth;
}
public Double perimeter() {
return 2 * length + 2 * breadth;
}
@Override
public void print() {
System.out.println("A " + name + " with length " + length
+ ", breadth " + breadth + ", area " + area()
+ " and perimeter " + perimeter() + ".");
}
}
Circle circle = new Circle(4d);
circle.print();
Rectangle rectangle = new Rectangle(2d, 5.5);
rectangle.print();

groovy

abstract class Shape {
final name
Shape(name) { this.name = name }
abstract area()
abstract print()
}

class Circle extends Shape {
final radius
Circle(radius) {
super('circle')
this.radius = radius
}
def area() { Math.PI * radius * radius }
def circumference() { 2 * Math.PI * radius }
def print() {
println "I am a $name with ->"
printf 'Radius: %.2f\n', radius
printf 'Area: %.2f\n', area()
printf 'Circumference: %.2f\n', circumference()
}
}

class Rectangle extends Shape {
final length, breadth
def Rectangle(length, breadth) {
super("rectangle")
this.length = length
this.breadth = breadth
}
def area() { length * breadth }
def perimeter() { 2 * length + 2 * breadth }
def print() {
println "I am a $name with ->"
printf 'Length, Width: %.2f, %.2f\n', length, breadth
printf 'Area: %.2f\n', area()
printf 'Perimeter: %.2f\n', perimeter()
}
}

shapes = [new Circle(4.2), new Rectangle(2.7, 3.1), new Rectangle(6.2, 2.6), new Circle(17.3)]
shapes.each { shape -> shape.print() }

scala

abstract class Shape (val name: String) {
def area : Double
def print()
}

class Circle (val radius: Double) extends Shape("Circle") {
def area = Math.Pi * radius * radius
def circumference = 2 * Math.Pi * radius
def print() {
println("I'm a " + name + " with")
printf(" * radius = %.2f\n", radius)
printf(" * area = %.2f\n", area)
printf(" * circumference = %.2f\n\n", circumference)
}
}

class Rectangle (val length: Double, val breadth: Double) extends Shape("Rectangle") {
def area = length * breadth
def perimeter = 2 * (length + breadth)
def print() {
println("I'm a " + name + " with")
printf(" * length = %.2f\n", length)
printf(" * breadth = %.2f\n", breadth)
printf(" * area = %.2f\n", area)
printf(" * perimeter = %.2f\n\n", perimeter)
}
}

val shapes = List(new Circle(5.4), new Rectangle(7.8, 6.5))
shapes foreach (_.print)

python

#Start with the import statements.
import math # necessary to get the value of pi

class Shape(object):
"""Shape Class"""
def __init__(self):
"""Constructor method"""
pass #Do nothing here
def area(self):
"""The area method"""
pass #Do nothing here
def print_(self):
"""
The print method. Note the trailing underscore - this is because
there is a reserved statement called 'print' in python 2.x. The
trailing underscore is the accepted method of re-using names without
rebinding them
"""
print 'The name is: %s' % self.name #Print the only property we currently have

def _getName(self):
"""The getter method for the 'name' property.
Note that getter methods are generally discouraged in python"""
return self._name

_name = None # The leading underscore gives a weak non-public value
# to a variable. Two leading underscores will mangle its
# name at runtime, to make it more difficult to access.
# Note there is no real 'private' variable type in python.
name = property(_getName, doc='The name of this object')
# property statements work like: property(fget=None, fset=None, fdel=None, doc=None)

class Circle(Shape):
"""Circle Class - a sub class of shape"""
def __init__(self, radius, name='Circle'):
"""Constructor method again"""
Shape.__init__(self) # init the super class
self.radius = radius # Store the radius
self._setCircumference()# Function call
self._name = name

def _setCircumference(self):
self.circumference = 2*math.pi*self.radius

def area(self):
'''Return the area of this circle'''
tmpAera = math.pi * self.radius**2
return tmpAera
def print_(self):
'''The print method'''
super(Circle, self).print_() # This calls the print_ method in
# the super classes of Circle, in
# this case Shape
print 'The radius is: %f' % self.radius
print 'The circumference is %f' % self.circumference
print 'The area is: %f' % self.area()

class Rectangle(Shape):
"""The Rectangle Class"""
def __init__(self, length, breadth, name='Rectangle'):
Shape.__init__(self)
self._name = name
self.length = length
self.breadth = breadth
self.perimeter()
def area(self):
return self.breadth*self.length
def perimeter(self):
self._perimeter = self.breadth*2+self.length*2
return self._perimeter # You have a method return a value and still
# safely call it without handling the return
# value. This would be collected by garbage
# collection.
def print_(self):
super(Rectangle, self).print_()
print 'The length is %f and the breadth is %f' %(self.length, self.breadth)
print 'The perimeter is: %f' %self._perimeter
print 'The area is: %f' % self.area()

if __name__ == '__main__':
rectangle = Rectangle(5,3)
circle = Circle(5, name='Round and Round')
rectangle.print_()
circle.print_()

fsharp

[<AbstractClass>]
type Shape(name:string) =
member this.Name = name
abstract Area : float
abstract Print : unit -> unit

type Circle(name, radius:float) =
inherit Shape(name)
member this.Radius = radius
member this.Circumference =
System.Math.PI * radius * 2.
override this.Area =
System.Math.PI * radius * radius
override this.Print() =
printfn "Circle: %s" this.Name
printfn "Area: %f" this.Area
printfn "Circumference: %f" this.Circumference
printfn "Radius: %f" this.Radius

type Rectangle(name, length:float, breadth:float) =
inherit Shape(name)
member this.Length = length
member this.Breadth = breadth
member this.Perimiter =
(length * 2.) + (breadth * 2.)
override this.Area =
length * breadth
override this.Print() =
printfn "Rectangle: %s" this.Name
printfn "Area: %f" this.Area
printfn "Perimiter: %f" this.Perimiter
printfn "Length: %f" this.Length
printfn "Breadth: %f" this.Breadth

let c = Circle("Foo", 2.1)
let r = Rectangle("Bar", 2.2, 3.3)

c.Print()
printfn ""
r.Print()

csharp

// While abstract classes do exist in C#, it is most common to use
// an interface in this type of situation.
// It is a common idiom to prefix interface names with an I
public interface IShape {
string Name { get; }
double Area { get; }
void Print();
}

public class Circle : IShape {

private double Radius { get; set; }
public Circle(double radius) {
Name = "Circle";
Radius = radius;
}

public string Name { get; private set; }
public double Area {
get {
return Math.PI * Radius * Radius;
}
}
public double Circumference {
get {
return Math.PI * (Radius + Radius);
}
}

public void Print() {
Console.WriteLine( " Name: {0}\n Area: {1}\n Circumference: {2}\n Radius: {3}",
this.Name,
this.Area,
this.Circumference,
this.Radius
);
}
}

public class Rectangle : IShape {

private double Length { get; set; }
private double Breadth { get; set; }
public Rectangle(double length, double breadth) {
Name = "Rectangle";
Length = length;
Breadth = breadth;
}

public string Name { get; private set; }
public double Area {
get {
return Length * Breadth;
}
}
public double Perimeter {
get {
return (Length * 2) + (Breadth * 2 );
}
}

public void Print() {
Console.WriteLine( " Name: {0}\n Area: {1}\n Perimeter: {2}\n Length: {3}\n Breadth: {4}",
this.Name,
this.Area,
this.Perimeter,
this.Length,
this.Breadth
);
}
}

// Driver
public class InheritanceHeirarchy {
public static void _Main() {
var c = new Circle(2.1);
c.Print();

Console.WriteLine();

var r = new Rectangle(2.2, 3.3);
r.Print();
}
}

php

<?php
abstract class Shape
{
protected $name;
abstract public function area ();
abstract public function _print ();
public function __construct ($name)
{
$this->name = $name;
}
}

class Circle extends Shape
{
protected $radius;
public function __construct ($radius)
{
parent::__construct('Circle');
$this->radius = $radius;
}
public function area ()
{
return pi() * $this->radius * $this->radius;
}
public function circumference ()
{
return 2 * pi() * $this->radius;
}
public function _print ()
{
print("I am a {$this->name} with ->\n");
print(" Radius: {$this->radius}\n");
print(" Area: {$this->area()}\n");
print(" Circumference {$this->circumference()}\n");
}
}

class Rectangle extends Shape
{
protected $length;
protected $breadth;
public function __construct ($length, $breadth)
{
parent::__construct('Rectangle');
$this->length = $length;
$this->breadth = $breadth;
}
public function area ()
{
return $this->length * $this->breadth;
}
public function perimeter ()
{
return (2 * $this->length) + (2 * $this->breadth);
}
public function _print ()
{
print("I am a {$this->name} with ->\n");
print(" Length, Width: {$this->length}, {$this->breadth}\n");
print(" Area: {$this->area()}\n");
print(" Perimeter: {$this->perimeter()}\n");
}
}

$shapes = array(new Circle(4.2) , new Rectangle(2.7, 3.1) , new Rectangle(6.2, 2.6) , new Circle(17.3));

foreach ($shapes as $shape) {
$shape->_print();
}

Implement and use an Interface

Create a Serializable interface consisting of 'save' and 'restore' methods, each of which:

* Accept a stream or handle or descriptor argument for the source or destination
* Save to destination or restore from source the properties or data members of the implementing class (restrict yourself to the primitive types 'int' and 'string')

Next, create a Person class which has 'name' and 'age' properties or data members and implements this interface. Instantiate a Person object, save it to a serial stream, and instantiate a new Person object by restoring it from the serial stream.

ruby

class Person
def initialize(name, age)
@name, @age = name, age
end
end

tom = Person.new("Tom Bones", 23)

File.open('tommy.dump', 'w+') {|f| f.write(Marshal.dump(tommy)) }
toms_clone = Marshal.load(File.read('tommy.dump'))

java

// Serialization to a file
class Person implements Serializable {
private static final long serialVersionUID = 1L;
private String name;
private int age;
public void setAge(int age) {
this.age = age;
}
public int getAge() {
return age;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public boolean equals(Object obj) {
if(obj == this) return true;
if(obj instanceof Person) {
Person p = (Person) obj;
return (p.getName().equals(this.getName())
& p.getAge() == this.getAge());
}
return false;
}
public String toString() {
return "Name: " + name + ", age: " + age;
}
}
Person person = new Person();
person.setName("Gaylord Focker");
person.setAge(21);

try {
File file = new File("ser.obj");
FileOutputStream fos = new FileOutputStream(file);
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(person);
oos.close();
FileInputStream fis = new FileInputStream(file);
ObjectInputStream ois = new ObjectInputStream(fis);
Person deserializedPerson = (Person) ois.readObject();
ois.close();
System.out.println(deserializedPerson);
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}

groovy

// Built-in functionality but with slightly different names. Showing usage:
class Person implements Serializable { String name; int age }
p1 = new Person(name:'John', age:21)
p2 = null
output = new ByteArrayOutputStream() // or FileOutputStream, etc.
output.withObjectOutputStream { oos -> oos << p1 }
input = new ByteArrayInputStream(output.toByteArray())
input.withObjectInputStream(getClass().classLoader){ ois -> p2 = ois.readObject() }
assert p2.name == 'John'
assert p2.age == 21

scala

class Person (var name: String, var age: Int) extends Serializable

val p1 = new Person("John", 21)
val output = new ByteArrayOutputStream()
val oos = new ObjectOutputStream(output)
oos.writeObject(p1)
oos.flush
oos.close

val input = new ByteArrayInputStream(output.toByteArray())
val ois = new ObjectInputStream(input)
val p2 = ois.readObject().asInstanceOf[Person]

assert(p2.name == "John")
assert(p2.age == 21)

python

import pickle

class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def __str__(self):
return "Name: {name}, age: {age}".format(name=self.name, age=self.age)

person = Person("Gaylord Focker", 21)
with open("person.pickle", "wb") as outstream:
pickle.dump(person, outstream)
with open("person.pickle", "rb") as instream:
deserialized_person = pickle.load(instream)
print(deserialized_person)

fsharp

// Since everyone else is using built-in functionality instead of
// defining an interface as required, I won't buck the trend.
// Maybe this problem should be named "Use serialization features" instead
// of "Implement and use an Interface"

open System
open System.IO
open System.Runtime.Serialization.Formatters.Binary

[<Serializable>]
type Person(name:string, age:int) =
member this.Name = name
member this.Age = age

let serialize x =
use ms = new MemoryStream()
let bf = new BinaryFormatter()
bf.Serialize(ms, x)
ms.ToArray()

let deserialize<'a> bytes =
use ms = new MemoryStream(bytes:byte[])
let bf = new BinaryFormatter()
bf.Deserialize(ms) :?> 'a

let before = Person("Joel", 35)
let bytes = serialize before
let after = deserialize<Person> bytes

printfn "Before: %s, %i" before.Name before.Age
printfn "After: %s, %i" after.Name after.Age

php

class Person implements Serializable {
private $name;
private $age;
public function __construct($name, $age) {
$this->name = $name;
$this->age = $age;
}
public function serialize() {
return serialize(array($this->name, $this->age));
}
public function unserialize($serialized) {
list($this->name, $this->age) = unserialize($serialized);
}
public function getData() {
return array($this->name, $this->age);
}
}

$obj = new Person('Gaylord Focker', 21);
file_put_contents('person.dump', serialize($obj));

$newobj = unserialize(file_get_contents('person.dump'));

var_dump($newobj->getData());

Networking

HTTP

Check your language appears on the langref.org site

Your language name should appear within the HTML found at the http://langreg.org main page.

ruby

Net::HTTP.start(URL, 80) do |http|
status = if http.get('/').body =~ /#{SRCHEXP}/ then "offers" else "does not offer" end
puts "http:\/\/#{URL} #{status} #{LANGUAGE}"
end

java

String url = "http://langref.org/", language = "java", line = null, regexp = ".*" + url + language + ".*";

BufferedReader in = new BufferedReader(new InputStreamReader((new URL(url)).openStream()));
while ((line = in.readLine()) != null)
if (line.matches(regexp)) { System.out.printf("Language %s exists @ %s\n", language, url); break; }

in.close();

perl

# requires libwww-perl
use LWP::Simple;

if (grep /perl/, get('http://langref.org/')) {
print 'perl appears on langref.org';
} else {
print 'perl does not appear on langref.org';
}

groovy

assert new URL('http://langref.org').text.contains('groovy')

scala

val url = "http://langref.org/" ; val language = "scala" ; val srchexp = url + language;

val source = Source.fromURL(url).getLines

while (source.hasNext) if (source.next.contains(srchexp)) printf("Language %s exists @ %s\n", language, url)

python

from urllib import urlopen
print urlopen('http://langref.org').read().find('python') >= 0 and 'found' or 'not found'

cpp

HttpWebRequest^ httpReq = safe_cast<HttpWebRequest^>(WebRequest::Create(url)); httpReq->KeepAlive = false;
StreamReader^ httpStream = gcnew StreamReader(httpReq->GetResponse()->GetResponseStream());
String^ htmlPage = httpStream->ReadToEnd(); httpStream->Close();

Console::WriteLine("{0} {1} {2}", url, (htmlPage->IndexOf(url + language) > 0 ? "offers" : "does not offer"), language);

fsharp

let httpReq = (WebRequest.Create(url) :?> HttpWebRequest)
httpReq.KeepAlive <- false
let httpStream = new StreamReader(httpReq.GetResponse().GetResponseStream())
let htmlPage = httpStream.ReadToEnd()
httpStream.Close()

let offerStatus = (if (htmlPage.IndexOf(url ^ language) > 0) then "offers" ; else "does not offer")
Console.WriteLine("{0} {1} {2}", url, offerStatus, language)

erlang

URL = "http://langref.org/", Language = "erlang", Regexp = ".*" ++ URL ++ Language ++ ".*",

case http:request(URL) of
{ok, {_, _, Body}} ->
case regexp:first_match(Body, Regexp) of
{match, _, _} -> io:format("Language ~s exists @ ~s~n", [Language, URL]);
_ -> false
end;
{error, ErrorInfo} -> throw("Error: " ++ http:format_error(ErrorInfo))
end,

php

if (preg_match("/PHP/i", file_get_contents("http://langref.org/"))) {
echo "PHP appears on langref.org";
} else {
echo "PHP doesn't appear on langref.org";
}

SMTP

Send an email

Use library functions, classes or objects to create a short email addressed to your own email address. The subject should be, "Greetings from langref.org", and the user should be prompted for the message body, and whether to cancel or proceed with sending the email.

ruby

require 'net/smtp'
require 'webrick/utils'

body = <<END_OF_MESSAGE
This is a message from langref.org
END_OF_MESSAGE

SMTPSRV = 'smtp.somewhere.com'
USER = 'me' ; DOMAIN = 'somewhere.com' ; FROM = USER + '@' + DOMAIN
TO = 'dest@somewhereelse.com'
SUBJECT = 'Greetings from langref.org'
DATE = Time.now.rfc2822()
MSGID = '<' + WEBrick::Utils.random_string(21) + '.' + WEBrick::Utils.random_string(21) + '@' + SMTPSRV + '>'

Net::SMTP.start(SMTPSRV, 25) do |smtp|
smtp.open_message_stream(FROM, [TO]) do |msg|
msg.puts "From: #{FROM}"
msg.puts "To: #{TO}"
msg.puts "Subject: #{SUBJECT}"
msg.puts "Date: #{DATE}"
msg.puts "Message-ID: #{MSGID}"
msg.puts
msg.puts body
end
end

java

// requires Java Mail API (mail.jar), which must be in classpath
try {
Properties props = System.getProperties();
props.put("mail.smtp.host", "smtp.sampledomain.com");
Session session = Session.getDefaultInstance(props, null);
Message msg = new MimeMessage(session);
msg.setFrom(new InternetAddress("gaylord.focker@hollywood.com"));
msg.setRecipients(Message.RecipientType.TO, InternetAddress.parse("father@family.com"));
msg.setRecipients(Message.RecipientType.CC, InternetAddress.parse("mother@family.com"));
msg.setSubject("subject");
msg.setText("message body");
msg.setHeader("X-Mailer", "jAVAmAILER");
msg.setSentDate(new Date());
Transport.send(msg);
} catch (AddressException e) {
e.printStackTrace();
} catch (MessagingException e) {
e.printStackTrace();
}

perl

#SendSimpleEmail.pl
#
# Uses NET::SMTP to send an email to a specific email address
#Modification History
# 2009-MAR-17: GGARIEPY: [creation] (note: geoff.gariepy@gmail.com)

use strict;
use Net::SMTP; # See http://search.cpan.org/~gbarr/libnet-1.22/Net/SMTP.pm

my $smtpserver = 'some.smtp.server.fqdn.com'; # FQDN of SMTP server
my $fromaddress = 'somebody.surname@someemail.com';# Authorized user of SMTP server
my $subject = 'Greetings from langref.org'; # Subject of the message
my $recipient = 'geoff.gariepy@gmail.com'; # Recipient address
my @now;

# Prompt user for the message body to send
print "Enter the body of the message to send, then press Enter >";
my $message = <STDIN>; # String containing the body of the email

# Prompt user to see if execution should continue
print "Open connection to SMTP server [$smtpserver] to send your message? y/N [N] >";
my $yesorno = <STDIN>;
unless ($yesorno =~ /y/i ) {
print "Aborting send of message\n";
exit;
}

my $smtp = Net::SMTP->new($smtpserver, Debug => 1);# Connect to the SMTP server, and
# output diagnostics to STDOUT (DEBUG mode)

# Check to make sure connection was established; die if not.
if (!ref($smtp)) {
die("SENDMAIL: Couldn't establish session with $smtpserver! Message not sent!\n");
}

# Start the communication with the SMTP server by telling it we want
# to mail something.
$smtp->mail($fromaddress);

# Perl's NET::SMTP interface specifies the recipient(s) of the message by
# calls to the recipient method.
# Note that the method should be called once for each separate recipient
# (set up a loop to do this.)
# We're only going to do it once, however, since we only have one recipient.
$smtp->recipient($recipient);

# Figure out current date/time for the message date stamp
# Date stamp format is DD Monthname YY HH:MM:SS TIMEZONE
my @monthnames = qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec);
@now = gmtime(time);
for (0..$#now) {
# Make single-digit date/time elements two digits
if (length($now[$_]) lt 2) {$now[$_] = '0'.$now[$_];} # (i.e. prefix with '0')
}

# Slice off just the time and date elements we need from the output of gmtime()
my($YY, $MON, $DD, $HH, $MM, $SS) = @now[5,4,3,2,1,0];
$YY += 1900; # gmtime() epoch starts at 1900

my $monthname = $monthnames[$MON]; # Get the name of the month

# Finally build the silly date stamp!
my $datestring = "Date: $DD $monthname $YY $HH:$MM:$SS GMT";

# Tell the SMTP server we're about to send a block of message data
$smtp->data();
$smtp->datasend("$datestring"); # Give it the message date stamp
$smtp->datasend("From: $fromaddress\n"); # Send from address
$smtp->datasend("To: $recipient\n"); # Build the *display* list of 'to:' addresses
$smtp->datasend("Subject: $subject\n\n"); # Send subject delimited by two CRLFs
$smtp->datasend($message); # Send the message body
$smtp->dataend(); # Actually sends the message!!
$smtp->quit(); # Close the link to the SMTP server

__END__

groovy

// numerous libraries exist, this uses ant
// needs these jars: mailapi.jar, smtp.jar, ant-javamail.jar, ant-nodeps.jar
new AntBuilder().with {
input(message:'Message to send:', addproperty:'body')
input(message:'Send email?', validargs:'y,n,Y,N', addproperty:'confirm')
condition(property:'abort') { matches(string:'${confirm}', pattern:'n|N') }
fail(if:'abort', 'Email send aborted by user')
mail(mailhost:'smtp.gmail.com', mailport:'465', ssl:'on', user:'you@gmail.com',
subject:'Greetings from langref.org', password:'your_password'){
from(address:'you@gmail.com')
to(address:'rob@langref.org')
message('${body}')
}
}

scala

// requires Java Mail API (mail.jar), which must be in classpath

import javax.mail._
import javax.mail.internet._
import java.util.Properties._

// Get the user's message
println("Enter the text you wish to send in the message (hit Ctrl-D to finish):")
var bodyText = ""
var line = readLine
while (line != null) {
bodyText += line
line = readLine
}

// Confirm they want to send
println("Are you sure you want to send the message? [y/N]")
val yesOrNo = readLine
if (yesOrNo != "y" && yesOrNo != "Y") {
println("Aborted")
exit
}

// Set up the mail object
val properties = System.getProperties
properties.put("mail.smtp.host", "localhost")
val session = Session.getDefaultInstance(properties)
val message = new MimeMessage(session)

// Set the from, to, subject, body text
message.setFrom(new InternetAddress("test@example.org"))
message.setRecipients(Message.RecipientType.TO, "spam@mopoke.co.uk")
message.setSubject("Greetings from langref.org")
message.setText(bodyText)

// And send it
Transport.send(message)

python

import smtplib
import locale

from email.mime.text import MIMEText

encoding = locale.getpreferredencoding()

def main():
smtp_servername = "smtp.example.com"

from_addr = "ernie@example.com"
to_addr = "cookie.monster@mailinator.com"

body = raw_input("Enter the email message ")
if not raw_input("Send email? y/N ") in ["y", "Y"]:
print "aborting"
return

message = MIMEText(body, _charset=encoding)

message["From"] = from_addr
message["To"] = to_addr
message["Subject"] = "Greetings from langref.org"

server = smtplib.SMTP(smtp_servername)
server.sendmail(from_addr, to_addr, message.as_string())

if __name__ == "__main__":
main()

php

/* This is a version without any prompt – use it for a website */
$to = "mail@domain.tld";
$subject = "Greetings from langref.org";
$body = "Hi,\n\nHow are you?";
$headers = "From: sender@domain.tld\n"; // you can comment this out and delete it from below
if (mail($to, $subject, $body, $headers)) {
echo "Success";
}

/****
* For some (security)reason I couldn't
* submit this without adding a space to
* the functionnames. Please remove it :)
* in this case, only "f write" and "f gets"
****/

$to = "mail@domain.tld";
f write(STDOUT, "Mail: ".$to."\n");
$subject = "Greetings from langref.org";
f write(STDOUT, "Subject: ".$subject."\n");
f write(STDOUT, "Please type the body. Use \\n for newlines: \n");
$body = trim(f gets(STDIN)); // we get input
if ($body == "") { // if empty input
$body = "Hi! How are you?";
f write(STDOUT, "Using standard body: ".$body."\n");
}
f write(STDOUT, "Would you like to send the mail? [y/n]: ");
if (trim(f gets(STDIN)) == "y") {
if (mail($to, $subject, $body)) {
f write(STDOUT, "Success\n");
} else { // fallback
f write(STDOUT, "Failed to mail\n");
}
} else { // fallback
f write(STDOUT, "I'm sorry :(\n");
}

XML

Parsing

Process an XML document

Given the XML Document:

<shopping>
<item name="bread" quantity="3" price="2.50"/>
<item name="milk" quantity="2" price="3.50"/>
</shopping>

Print out the total cost of the items, e.g. $14.50

ruby

#!/usr/bin/env ruby

# needed to parse xml
require 'rexml/document'

# grab the file
file = File.new('shop.xml')

# load it as an xml document
doc = REXML::Document.new(file)

# initialize the total to 0 as a float
total = 0.0

# cycle through the items
doc.elements.each('shopping/item') do |item|

# add the price to the total
total += item.attributes['price'].to_f
end

# round the total to the nearest 0.01
total = (total*100.0).round/100.0

# pad the output with the proper number of trailing 0's
printf "$%.2f\n", total

java

// solution uses JAXP and SAX included in Java API since version >= 1.5
class ShoppingContentHandler extends DefaultHandler {
Double priceSum = 0d;
@Override
public void startElement(String uri, String localName, String name,
Attributes attributes) throws SAXException {
if(name.equals("item")) {
String quantityString = attributes.getValue(attributes.getIndex("quantity"));
String priceString = attributes.getValue(attributes.getIndex("price"));
Integer quantity = Integer.parseInt(quantityString);
Double price = Double.parseDouble(priceString);
priceSum += (quantity * price);
}
}
public Double getPriceSum() {
return priceSum;
}
}

SAXParserFactory parserFactory = SAXParserFactory.newInstance();
try {
SAXParser parser = parserFactory.newSAXParser();
XMLReader reader = parser.getXMLReader();
ShoppingContentHandler contentHandler = new ShoppingContentHandler();
reader.setContentHandler(contentHandler);
reader.parse(new InputSource(new FileReader("shopping.xml")));
System.out.printf("$%.2f", contentHandler.getPriceSum());

} catch (ParserConfigurationException e) {
e.printStackTrace();
} catch (SAXException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}

perl

#! /usr/bin/perl
# -*- Mode: CPerl -*-

use strict;
use XML::Simple;
use Data::Dumper;

# Given the XML Document:
#
# <shopping>
# <item name="bread" quantity="3" price="2.50"/>
# <item name="milk" quantity="2" price="3.50"/>
# </shopping>
#
# Print out the total cost of the items, e.g. $14.50

my $xml =
" <shopping>\n"
." <item name=\"bread\" quantity=\"3\" price=\"2.50\"/>\n"
." <item name=\"milk\" quantity=\"2\" price=\"3.50\"/>\n"
." </shopping>\n";

my $xs = XML::Simple->new();
my $ref = $xs->XMLin($xml);
my $stuff = ${$ref}{item};

my $q;
my $p;
my $t;
my $z;

foreach my $item ( sort keys %{$stuff}){
$q = ${$stuff}{$item}{quantity};
$p = ${$stuff}{$item}{price};
$z = $q*$p;
printf "%5.5s %2d @\$%5.2f = \$%5.2f\n",$item,$q,$p,$z;
$t += $z;
}
printf "Total \$%5.2f\n",$t;

#eos

groovy

printf '$%.2f\n', new XmlSlurper().parseText(xml).item.collect{
it.@quantity.toInteger() * it.@price.toFloat()
}.sum()

scala

val data = <shopping>
<item name="bread" quantity="3" price="2.50"/>
<item name="milk" quantity="2" price="3.50"/>
</shopping>

val res = for (
item <- data \ "item" ;
price = (item \ "@price").text.toDouble ;
qty = (item \ "@quantity").text.toInt)
yield (price * qty)

printf("$%.2f\n", res.sum)

python

from xml.dom.minidom import parseString
document = parseString(
"""<shopping>
<item name="bread" quantity="3" price="2.50"/>
<item name="milk" quantity="2" price="3.50"/>
</shopping>""").documentElement
total = sum([float(item.getAttribute('price')) *
int(item.getAttribute('quantity'))
for item in document.getElementsByTagName('item')])
print '$%.2f' % total

fsharp

#r @"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\v3.5\System.Xml.Linq.dll"

open System
open System.Xml.Linq
//XElement Helper
let xname sname = XName.Get sname

let xmlsnippet =
let snippet = new XElement(xname "shopping")
//create bread
let bread = new XElement(xname "item")
bread.SetAttributeValue(xname "name","bread")
bread.SetAttributeValue(xname "quantity",3)
bread.SetAttributeValue(xname "price",2.50)
//add bread to snippet
snippet.Add(bread)
//create milk
let milk = new XElement(xname "item")
milk.SetAttributeValue(xname "name","milk")
milk.SetAttributeValue(xname "quantity",2)
milk.SetAttributeValue(xname "price",3.50)
//add milk to snippet
snippet.Add(milk)
snippet

let totalprice (xe: XElement) =
xe.Descendants(xname "item")
|> Seq.map(fun i -> Double.Parse(i.Attribute(xname "price").Value))
|> Seq.fold(fun acc x -> acc + x) 0.0

erlang

-include_lib("xmerl/include/xmerl.hrl").
-export([get_total/1]).

get_total(ShoppingList) ->
{XmlElt, _} = xmerl_scan:string(ShoppingList),
Items = xmerl_xpath:string("/shopping/item", XmlElt),
Total = lists:foldl(fun(Item, Tot) ->
[#xmlAttribute{value = PriceString}] = xmerl_xpath:string("/item/@price", Item),
{Price, _} = string:to_float(PriceString),
[#xmlAttribute{value = QuantityString}] = xmerl_xpath:string("/item/@quantity", Item),
{Quantity, _} = string:to_integer(QuantityString),
Tot + Price*Quantity
end,
0, Items),
io:format("$~.2f~n", [Total]).

csharp

System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
doc.LoadXml(
@"<shopping>
<item name='bread' quantity='3' price='2.50'/>
<item name='milk' quantity='2' price='3.50'/>
</shopping>");

string decimalSeparator= System.Globalization.CultureInfo.CurrentCulture.NumberFormat.CurrencyDecimalSeparator;

double sum=0;

foreach(System.Xml.XmlNode nodo in doc.SelectNodes("/shopping/item")){
sum += int.Parse(nodo.Attributes["quantity"].InnerText) * double.Parse(nodo.Attributes["price"].InnerText.Replace(".",decimalSeparator));
}
Console.WriteLine("{0:#.00}",sum);

php

$xmlfile = simplexml_load_file('shop.xml');
$x = 0;
foreach ($xmlfile as $xml) {
// we have to declare that it's a float
$x = $x + ($xml['quantity'] * (float)$xml['price']);
}
echo $x;

$filename = "shop.xml";
if (($fp = fopen($filename, "r"))) {
while ($data = fread($fp, 4096)) {
$data = eregi_replace(">"."[[:space:]]+"."< ",">< ", $data);
if (!xml_parse($xmlparser, $data, feof($fp))) {
$reason = xml_error_string(xml_get_error_code($xmlparser));
$reason .= xml_get_current_line_number($xmlparser);
die($reason);
}
}
xml_parser_free($xmlparser);
echo $total; // Echo the total
}

Creation

create some XML programmatically

Given the following CSV:

bread,3,2.50
milk,2,3.50

Produce the equivalent information in XML, e.g.:

<shopping>
<item name="bread" quantity="3" price="2.50" />
<item name="milk" quantity="2" price="3.50" />
</shopping>

java

// In this solution JAXB is used to created the xml output.
// JAXB is included in Java 1.6. Runs with 1.5 if you include JAXB Jars
// in the classpath.
class Item {
// Of course you use getters and setters and declare attributes private.
// In this sample a "dirty" way is chosen to keep LOC low.
@XmlAttribute
String name;
@XmlAttribute
Integer quantity;
@XmlAttribute
Double price;
}

@XmlRootElement
class Shopping {
@XmlElement
Set<Item> items = new HashSet<Item>();
}

String line = null;
Shopping shopping = new Shopping();
try {
BufferedReader reader = new BufferedReader(new FileReader("shopping.csv"));
while ((line = reader.readLine()) != null) {
String[] parts = line.split(",");
Item item = new Item();
item.name = parts[0];
item.quantity = Integer.parseInt(parts[1]);
item.price = Double.parseDouble(parts[2]);
shopping.items.add(item);

}
JAXB.marshal(shopping, "D:" + File.separatorChar + "shopping.auto.xml");
} catch (IOException e) {
e.printStackTrace();
}

perl

#! /usr/bin/perl
# -*- Mode: CPerl -*-

use strict;
use XML::Simple;
use Data::Dumper;

# bread,3,2.50
# milk,2,3.50
#
# Produce the equivalent information in XML, e.g.:
#
# <shopping>
# <item name="bread" quantity="3" price="2.50" />
# <item name="milk" quantity="2" price="3.50" />
# </shopping>
#

my $line;
my $item;
my $q;
my $p;
my $z;

my $xs = XML::Simple->new();
my %d = ();
while($line=<DATA>){
chomp $line;
($item,$q,$p) = split ",",$line;
$d{shopping}{item}{$item}{quantity} = $q;
$d{shopping}{item}{$item}{price} = $p;
}

$xml = $xs->XMLout(\%d, KeepRoot => 1);
print $xml,"\n";

__DATA__
bread,3,2.50
milk,2,3.50

groovy

b = new groovy.xml.MarkupBuilder()
b.shopping {
csv.eachLine { line ->
(n, q, p) = line.split(',')
item(name:n, quantity:q, price:p)
}
}

// Groovy equivalent of Java JAXB solution
@XmlAccessorType(NONE)
class Item {
@XmlAttribute String name
@XmlAttribute Integer quantity
@XmlAttribute Double price
}

@XmlAccessorType(NONE)
@XmlRootElement
class Shopping {
@XmlElement Set<Item> items = []
}

Shopping shopping = new Shopping()
csvtext.eachLine{ line ->
(n, q, p) = line.split(',')
shopping.items << new Item(name:n, quantity:q.toInteger(), price:p.toDouble())
}
JAXB.marshal shopping, System.out

scala

<shopping>
{List("bread,3,2.50", "milk,2,3.50") map { row =>
row split ","
} map { item =>
<item name={item(0)} quantity={item(1)} price={item(2)}/>
}}
</shopping>

python

from xml.dom import minidom

csv = """bread,3,2.50
milk,2,3.50"""

doc = minidom.Document()
shopping = doc.createElement("shopping")

for line in csv.split("\n"):
name, quantity, price = line.split(",")
el = doc.createElement("item")
el.setAttribute("name", name)
el.setAttribute("quantity", quantity)
el.setAttribute("price", price)
shopping.appendChild(el)

print shopping.toprettyxml()

fsharp

#r "System.Xml.dll"
#r "System.Xml.Linq.dll"

open System
open System.Xml
open System.Xml.Linq

let data = "bread,3,2.50
milk,2,3.50"

let X name =
XName.Get(name)

let lines = data.Split( [|"\n" |], StringSplitOptions.RemoveEmptyEntries)

let document = new XDocument()
let element = new XElement(X "shopping")
document.Add(element)

lines
|> Seq.iter (fun line ->
let items = line.Split([|','|])
let item = new XElement(X "item",
new XAttribute(X "name", items.[0]),
new XAttribute(X "quantity", items.[1]),
new XAttribute(X "price", items.[2]))
element.Add(item))

let output = document.ToString();;

erlang

to_xml(ShoppingList) ->
Items = lists:map(fun(L) ->
[Name, Quantity, Price] = string:tokens(L, ","),
{item, [{name, Name}, {quantity, Quantity}, {price, Price}], []}
end, string:tokens(ShoppingList, "\n")),
xmerl:export_simple([{shopping, [], Items}], xmerl_xml).

csharp

string cvs ="bread,3,2.50\nmilk,2,3.50";
IList<string> rows = cvs.Split('\n');

System.Text.StringBuilder sb = new System.Text.StringBuilder("<shopping>");
foreach(string row in rows){
IList<string> data = row.Split(',');
sb.AppendFormat("<item name='{0}' quantity='{1}' price='{2}' />",data[0],data[1],data[2]);
}
sb.Append("</shopping>");

php

$xmllines = split("\n", $cvs);
foreach ($xmllines as $l) {
$xml[] = split(",", $l);
}
echo "<shopping>\n";
foreach ($xml as $x) {
echo "\t<item name=\"".$x[0]."\" quantity=\"".$x[1]."\" price=\"".$x[2]."\" />\n";
}
echo "</shopping>\n";

Algorithms

Geometry

Find all Pythagorean triangles with length or height less than or equal to 20

Pythagorean triangles are right angle triangles whose sides comply with the following equation:

a * a + b * b = c * c

where c represents the length of the hypotenuse, and a and b represent the lengths of the other two sides. Find all such triangles where a, b and c are non-zero integers with a and b less than or equal to 20. Sort your results by the size of the hypotenuse. The expected answer is:

[3, 4, 5]
[6, 8, 10]
[5, 12, 13]
[9, 12, 15]
[8, 15, 17]
[12, 16, 20]
[15, 20, 25]

ruby

results=[]

1.upto(20) do |a|
1.upto(20) do |b|
c=Math.sqrt(a**2+b**2)
results<<[a, b, c.to_i] if c.to_i==c && !results.index([b, a, c.to_i])
end
end

results=results.sort_by{|r| r[2]}

puts results

java

SortedSet<List<Integer>> results = new TreeSet<List<Integer>>(new Comparator<List<Integer>>() {
public int compare(List<Integer> o1, List<Integer> o2) {
return o1.get(2).compareTo(o2.get(2));
}
});
for (int x = 1; x <= 20; x++) {
for (int y = 1; y <= 20; y++) {
double z = Math.hypot(x, y) ;
if ((int) z == z)
results.add(Arrays.asList( new Integer[] { x, y, (int) z }));
}
}

perl

#!/usr/bin/perl
my @results;
for my $x (1..20) {
for my $y ($x..20) {
my $z = sqrt($x**2+$y**2);
push @results, [$x,$y,$z] if $z == int($z);
}
}
for my $triangle ( sort { $a->[2] <=> $b->[2] } @results) {
print "[".join(',',@$triangle)."]\n";
}

groovy

Set results = []
for (x in 1..20)
for (y in x..20) {
def z = sqrt(x*x + y*y)
if (z.toInteger() == z) results << [x, y, z.toInteger()]
}
println results.sort{it[2]}.join('\n')

scala

val res = for (
x <- 1 to 20 ;
y <- x to 20 ;
z = Math.sqrt(x*x + y*y) ;
if (z.toInt == z) )
yield (x, y, z.toInt)

res.toList.sortWith { (t1, t2) =>
t1._3 < t2._3
} foreach (println(_))

(for(x <- 1 to 20;
y<- x to 20;
z<- 1 to 30;
if(z*z == x*x + y*y)) yield(x, y, z)
).sortWith(_._3 < _._3) foreach println

python

from math import sqrt

a = 1
ret = []
while a <= 20:
b = 1
while b <= 20:
c = sqrt((a**2)+(b**2))
if int(c) == c and sorted([a,b,int(c)]) not in ret:
ret.append(sorted([a,b,int(c)]))
b +=1
a +=1
print ret

or if you wanna get snarky..

print sorted(set([tuple(sorted((a,b,int(sqrt((a**2)+(b**2)))))) for a in xrange(1,21) for \
b in xrange(1,21) if int(sqrt((a**2)+(b**2))) == sqrt((a**2)+(b**2))]))

fsharp

let getGoodTri (a,b) =
let h = int(System.Math.Sqrt(float(a*a + b*b)))
if a*a + b*b = h*h then Some(a,b,h)
else None

seq{ for i in 1..20 do yield! seq{for j in i..20 do yield i,j} } |> Seq.choose(getGoodTri) |> Seq.sortBy(fun (_,_,c) -> c);;

erlang

find_all_pythagorean_triangles(L) ->
lists:sort(fun({_, _, H1}, {_, _, H2}) -> H1 =< H2 end,
[ { X, Y, Z } ||
X <- lists:seq(1,L),
Y <- lists:seq(1,L),
Z <- lists:seq(1,2*L),
X*X + Y*Y =:= Z*Z,
Y > X,
Z > Y
]).

main(_) ->
List = find_all_pythagorean_triangles(20).

php

for ($x = 1; $x <= 20; $x++) {
for ($y = $x; $y <= 20; $y++) {
$z = hypot($x, $y); // or $z = sqrt($x*$x + $y*$y);
if (round($z) == $z) {
$array = array($x, $y, $z);
sort($array, SORT_NUMERIC);
$res[] = $array;
}
}
}

// calculate the total of the sides
foreach ($res as $a) {
$total[] = ($a[0] + $a[1] + $a[2]);
}
array_multisort($total, $res); // and sort them after the total
// result is in $res

Misc

Fun

produces a copy of its own source code

In computing, a quine is a computer program which produces a copy of its own source code as its only output.

ruby

eval s=%q(puts"eval s=%q(#{s})")

java

public class Quine {public static void main(String[] args) {String s = "public class Quine {public static void main(String[] args) {String s = %c%s%c;System.out.printf(s, 34, s, 34);}}";System.out.printf(s, 34, s, 34);}}

public class Quine {
public static void main(String[] args) {
Character cq = (char) 34;
Character cn = (char) 10;
Character cs = (char) 92;
String s = "public class Quine {\n public static void main(String[] args) {\n Character cq = (char) 34;\n Character cn = (char) 10;\n Character cs = (char) 92;\n String s = %c%s%c;\n System.out.printf(s, cq, s.replace(cn.toString(), cs.toString() + 'n'), cq);\n }\n}";
System.out.printf(s, cq, s.replace(cn.toString(), cs.toString() + 'n'), cq);
}
}

perl

seek DATA,0,0;
print <DATA>;
__DATA__
Cheating quine.

$_=q(print qq(\$_=q($_);eval\n));eval

groovy

s="s=%s;printf s,s.inspect()";printf s,s.inspect()

evaluate s='char q=39;print"evaluate s=$q$s$q"'

s="s=%c%s%c;printf s,34,s,34";printf s,34,s,34

s='s=%c%s%1$c;printf s,39,s';printf s,39,s

printf _='printf _=%c%s%1$c,39,_',39,_

scala

val s="val s=%c%s%c; printf(s, 34, s, 34)"; printf(s, 34, s, 34)

python

# adapted from a Quine by Sean B. Palmer

print (lambda s='print (lambda s=%r: (s %% s))()': (s % s))()

ocaml

(fun s -> Printf.printf "%s %S" s s) "(fun s -> Printf.printf \"%s %S\" s s)"

php

// We make sure nothing else is outputted on the screen
ob_end_clean(); // Clean everything
die(highlight_file(__FILE__)); // Print and die

Parallel

Pool of Workers

Subdivide A Problem To A Pool Of Workers (No Shared Data)

java

public class ParallelPermutations {

final AtomicInteger cnt = new AtomicInteger(0);

final List<Set<String>> permutations = new ArrayList<Set<String>>();

public static void main(String[] args) {
new ParallelPermutations(Arrays.asList(args));
}

public ParallelPermutations(List<String> words) {
for (final String word : words) {
new Thread(new Runnable() {
public void run() {
cnt.incrementAndGet() ;
Set<String> permutationSet = new HashSet<String>();
for (int i = 0; i < word.length(); i++)
for (int j = i + 1; j <= word.length(); j++)
permutations("", word.substring(i, j),
permutationSet);
permutations.add(permutationSet);
if (cnt.decrementAndGet() == 0)
synchronized (ParallelPermutations.this) {
ParallelPermutations.this.notify();
}
}
private void permutations(String prefix, String word, Set<String> permutations) {
int N = word.length();
if (N == 0)
permutations.add(prefix);
else
for (int i = 0; i < N; i++)
permutations(
prefix + word.charAt(i),
word.substring(0, i) + word.substring(i + 1, N),
permutations);
}
}).start();
}

synchronized (this) {
try {
wait();
} catch (InterruptedException e) {
Thread.currentThread().isInterrupted();
}
}

System.out.println(permutations);
}

}

public class ParallelPermutations {
public static void main(String[] words) throws Exception {
if(words.length==0)
words = new String[] {"ab", "we", "tfe", "aoj"};

ParallelPermutations permutations = new ParallelPermutations();
Map<String,Set<String>> wordPermutationSet =
permutations.calculate(words);

for(Map.Entry<String,Set<String>> e : wordPermutationSet.entrySet())
System.out.println(e.getKey()+" > "+e.getValue());

System.out.println(permutations.getNumberOfJobSpawned ()+" job(s) have been spawned");
}

private AtomicInteger jobSpawnedCounter = new AtomicInteger();
private ExecutorService workers ;
private ConcurrentLinkedQueue<Future<PermutationTask>> jobSpawned = newQueue();

public ParallelPermutations () {
int availableProcessors = Runtime.getRuntime().availableProcessors();
// create a thread pool according to the number of proc.
workers = Executors.newFixedThreadPool(availableProcessors);
}

private void spawn(PermutationTask task) {
Future<PermutationTask> spawned = workers.submit(task);
jobSpawnedCounter.incrementAndGet();
jobSpawned.add(spawned);
}
public int getNumberOfJobSpawned () {
return jobSpawnedCounter.get();
}

public Map<String,Set<String>> calculate (String[] words)
throws InterruptedException, ExecutionException
{
// submit all tasks, they will spawn sub-tasks by themselves
for(String word:words)
spawn(new PermutationTask(word));

Map<String,Set<String>> wordPermutationSet = newMap ();
Future<PermutationTask> spawned;
while( (spawned=jobSpawned.poll()) != null) {
// this will wait until the result is available
// this should also handle the fact that a sub-task is spawn
// and then added in the 'jobSpawned' before its parent is done
PermutationTask task = spawned.get();

String word = task.getWord();
Set<String> founds = task.getPermutationSet();
Set<String> alreadyFounds = wordPermutationSet.get(word);
if(alreadyFounds!=null)
alreadyFounds.addAll(founds);
else
wordPermutationSet.put(word, founds);
}
return wordPermutationSet;
}

private class PermutationTask implements Callable<PermutationTask> {
private final Set<String> permutationSet = new HashSet<String>();
private final String word;
private final int initialPos;
private final Stack<Integer> indicesUsed;
public PermutationTask(String word) {
this(word, 0, new Stack<Integer>());
}

/** sub task entry point */
public PermutationTask(String word,
int initialPos,
Stack<Integer> indicesUsed) {
this.word = word;
this.initialPos = 0;
this.indicesUsed = indicesUsed;
}

/** the word this task is working on*/
public String getWord() {
return word;
}

/** permutations set of this task */
public Set<String> getPermutationSet() {
return permutationSet;
}

/**
* perform the task specific calculation
* @see Callable
*/
public PermutationTask call() throws Exception {
calculatePermutation(initialPos, indicesUsed);
return this;
}

/**
* The algorithm part of the problem. The main interest is the sub-task
* spawning. When Java 7 will be available there would be a better
* alternative with the built-in fork/join framework.
*/
private void calculatePermutation(int currentPos, Stack<Integer> indicesUsed) {
final int maxLetterPerWord = word.length();
if(indicesUsed.size()>=maxLetterPerWord) {
return;
}

final StringBuilder builder = new StringBuilder();
for (int i = 0, length = word.length(); i < length; i++) {
if(indicesUsed.contains(i) && distinctIndices)
continue;
indicesUsed.push(i);
if(indicesUsed.size()>=MIN_LETTER_PER_WORD) {
builder.setLength(0);
for(Integer index: indicesUsed)
builder.append(word.charAt(index));
permutationSet.add(builder.toString());
}
// spawn a sub task to perform the next pos. calculation
spawn(new PermutationTask(word, currentPos+1, copy(indicesUsed)));
indicesUsed.pop();
}
}
}

/* algorithm parameters : the minimum number of letter per word */
private static int MIN_LETTER_PER_WORD = 1;
/* allow duplicated letters in the word found */
private static boolean distinctIndices = true;

/* factory method */
private static <T> ConcurrentLinkedQueue<T> newQueue () {
return new ConcurrentLinkedQueue<T>();
}
/* factory method */
private static <K,V> Map<K,V> newMap () {
return new HashMap<K,V>();
}
/* factory method */
private static Stack<Integer> copy(Stack<Integer> stack) {
Stack<Integer> copy = new Stack<Integer>();
copy.addAll(stack);
return copy;
}
}

groovy

// as per Java answer, doesn't duplicate chars from input string, i.e. no 'aa'
def ans = [].asSynchronized()
def words = ["ab", "we", "tfe", "aoj"]
def threads = []

void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}

words.each { word ->
def t = Thread.start {
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
ans << wordAns
}
threads << t
}

threads.each{ it.join() }
println ans

// as per Java answer, doesn't duplicate chars from input string, i.e. no 'aa'
def ans = [].asSynchronized()
def words = ["ab", "we", "tfe", "aoj"]

void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}

withParallelizer {
words.eachParallel { word ->
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
ans << wordAns
}
}

println ans

Subdivide A Problem To A Pool Of Workers (Shared Data)

Take a hard to compute problem and split it up between multiple worker threads. In your solution, try to fully utilize available cores or processors. (I'm looking at you, Python!)

Note: In this question, there should be a need for shared state between worker threads while the problem is being solved.

Example:

-Conway Game of Life-

From Wikipedia:

The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, live or dead. Every cell interacts with its eight neighbors, which are the cells that are directly horizontally, vertically, or diagonally adjacent. At each step in time, the following transitions occur:

1. Any live cell with fewer than two live neighbours dies, as if caused by underpopulation.
2. Any live cell with more than three live neighbours dies, as if by overcrowding.
3. Any live cell with two or three live neighbours lives on to the next generation.
4. Any dead cell with exactly three live neighbours becomes a live cell.

The initial pattern constitutes the seed of the system. The first generation is created by applying the above rules simultaneously to every cell in the seed—births and deaths happen simultaneously, and the discrete moment at which this happens is sometimes called a tick (in other words, each generation is a pure function of the one before). The rules continue to be applied repeatedly to create further generations.

--However, for our purposes, we will assign a size to the game "board": 2^k * 2^k . That is, the board should be easy to subdivide.

Notice that in this problem, at each step or "tick", each thread/process will need to share data with its neighborhood.

groovy

// some crude assumptions made for size and amount of parallelism
enum State { ALIVE, DEAD }
import static State.*

seed = '''\
* *
** **
** *
*
**
***
**
* \
'''

def computeNextGen(inboard, outboard, n) {
// crudely split into 4 chunks but could be smarter if we wanted
int half = n/2
def t1 = Thread.start { computeNextGen(inboard, outboard, n, 0, half, 0, half) }
def t2 = Thread.start { computeNextGen(inboard, outboard, n, 0, half, half, n) }
def t3 = Thread.start { computeNextGen(inboard, outboard, n, half, n, 0, half) }
def t4 = Thread.start { computeNextGen(inboard, outboard, n, half, n, half, n) }
[t1, t2, t3, t4].each{ it.join() }
}

def computeNextGen(inboard, outboard, n, minx, maxx, miny, maxy) {
for (int i = minx; i < maxx; i++)
for (int j = 0; j < maxy; j++)
if (i == 0 || i == n-1 || j == 0 || j == n-1)
outboard[i][j] = DEAD
for (int i = minx; i < maxx; i++) {
for (int j = miny; j < maxy; j++) {
if (i == 0 || i == n-1 || j == 0 || j == n-1)
continue
int count = 0
[[-1, 0, 1], [-1, 0, 1]].combinations().each{ dx, dy ->
if ((dx || dy) && inboard[i+dx][j+dy] == ALIVE) count++
}
switch(count) {
case {count == 3}:
case {inboard[i][j] == ALIVE && count == 2}:
outboard[i][j] = ALIVE; break
default:
outboard[i][j] = DEAD
}
}
}
}

void printBoard(board) {
println '--------'
println board*.collect{ it == DEAD ? ' ' : '*' }*.join().join('\n')
}

void initBoard(seed, board) {
def row = 0
seed.readLines().each { line ->
def col = 0
line.each { ch ->
board[row][col++] = ch == '*' ? ALIVE : DEAD
}
row++
}
}

def N = 8
def NUM_CYCLES = 3
def board1 = new State[N][N]
def board2 = new State[N][N]
initBoard(seed, board1)
NUM_CYCLES.times {
computeNextGen board1, board2, N
printBoard board2
computeNextGen board2, board1, N
printBoard board1
}

Threads

Create a multithreaded "Hello World"

Create a program which outputs the string "Hello World" to the console, multiple times, using separate threads or processes.

Example:

-Output-

Thread one says Hello World!
Thread two says Hello World!
Thread four says Hello World!
Thread three says Hello World!

-Notice that the threads can print in any order.

java

for (int i = 0; i < 4; i++) {
final int nr = i ;
new Thread(new Runnable() {
public void run() {
System.out.println("Thread " + new String[] { "one", "two", "three", "four" }[nr] + " says Hello World!");
}
}).start();
}

groovy

["one","two","three","four"].each { tid ->
Thread.start {
println "Thread $tid says Hello World!"
}
}

import static groovyx.gpars.Parallelizer.*
withParallelizer {
["one","two","three","four"].eachParallel {
println "Thread $it says Hello World!"
}
}

scala

import scala.actors.Actor

List("one", "two", "three", "four").foreach { name =>
new Actor { override def act() = { println("Thread " + name + " says Hello World!") } }.start
}

List("one", "two", "three", "four").foreach { name =>
new Thread { override def run() = { println("Thread " + name + " says Hello World!") } }.start
}

python

#!/usr/bin/python
from threading import Thread
Nthread = ['one','two','three','four']
def ThreadSpeaks(number):
print "Thread", number, "says Hello World!"
if __name__ == "__main__":
for n in range(0,len(Nthread)):
th =Thread(target=ThreadSpeaks, args=(Nthread[n],))
th.start()

cpp

#include <iostream>
#include <string>

using namespace std;

int main(){
int pid;
string text[4]={"one","two","three","four"};
for (int i=0;i<4;i++){
pid=fork();
if (pid>0){
//cout << "Process("<<pid<<") - " << "Thread " << text[i] << " says Hello World!" << endl;
cout << "Thread " << text[i] << " says Hello World!" << endl;
exit(0);
}
}
return 0;
}

fsharp

let mappedString =
["Thread one says Hello World!";
"Thread two says Hello World!";
"Thread four says Hello World!";
"Thread three says Hello World!"]
|> Seq.map (fun str -> async { printfn "%s" str })

Async.RunSynchronously (Async.Parallel mappedString)

erlang

-module(spam).
-export([spam/1]).

spam(N) when N<5 ->
spawn(fun() -> io:format("Hello World from thread ~p~n",[N]) end),
spam(N+1);
spam(_) -> void.

php

/*
The commented lines below can be used to verify new process are in use
*/
$text=array("one","two","three","four");
for ($i = 0; $i < 4; ++$i) {
$pid = pcntl_fork();
//$mypid=getmypid();
if (!$pid) {
//echo("Thread ".$text[$i]." says Hello World!(".$mypid.")\n");
echo("Thread ".$text[$i]." says Hello World!\n");
exit($i);
}
}

clojure

(doseq [msg ["one" "two" "three" "four"]]
(future (println "Thread" msg "says Hello World!")))

Create read/write lock on a shared resource.

Create multiple threads or processes who are either readers or writers. There should be more readers then writers.

(From Wikipedia):

Multiple readers can read the data in parallel but an exclusive lock is needed while writing the data. When a writer is writing the data, readers will be blocked until the writer is finished writing.

Example:

-Output-

Thread one says that the value is 8.
Thread three says that the value is 8.
Thread two is taking the lock.
Thread four tried to read the value, but could not.
Thread five tried to write to the value, but could not.
Thread two is changing the value to 9.
Thread two is releasing the lock.
Thread four says that the value is 9.
...

--Notice that when a needed resource is locked, a thread can set a timer and try again in the future, or wait to be notified that the resource is no longer locked.

java

public class ParallelPermutations {

Lock lock = new ReentrantLock();

Integer value = 8;

public static void main(String[] args) {
new ParallelPermutations(Arrays.asList(args));
}

public ParallelPermutations(List<String> words) {
for (int i = 0; i < 20; i++) {
final Integer cnt = i ;
if ( i % 3 == 0) {
new Thread(new Runnable() {
public void run() {
if ( ! lock.tryLock() ) {
System.out.println("Thread " + cnt + " tried to write the value, but could not.") ;
lock.lock();
}
value = (int) (Math.random() * 10);
System.out.println("Thread " + cnt + " is changing the value to " + value ) ;
lock.unlock();
System.out.println("Thread " + cnt + " is releasing the lock.") ;
}
}).start();
} else {
new Thread(new Runnable() {
public void run() {
if ( ! lock.tryLock() ) {
System.out.println("Thread " + cnt + " tried to read the value, but could not.") ;
lock.lock() ;
}
System.out.println("Thread " + cnt + " says that the value is " + value + ".") ;
lock.unlock();
}
}).start();
}
}
}
}

groovy

def lock = new ReentrantLock()
Integer value = 8

20.times { i ->
if (i % 3 == 0) {
Thread.start {
if (!lock.tryLock()) {
println "Thread " + i + " tried to write the value, but could not."
lock.lock()
}
value = (int) (Math.random() * 10)
println "Thread " + i + " is changing the value to " + value
lock.unlock()
println "Thread " + i + " is releasing the lock."
}
} else {
Thread.start {
if (!lock.tryLock()) {
println "Thread " + i + " tried to read the value, but could not."
lock.lock()
}
println "Thread " + i + " says that the value is " + value + "."
lock.unlock()
}
}
}

python

#!/usr/bin/python
from threading import Thread, Lock
import time
thread_readers = ['one','two','three']
thread_writer = ['four','five']
lock = Lock()
value = 0

def Threadread(number):
global value
while True:
if lock.acquire(False):
print "Thread", number, "is taking the lock"
value += 1
print "Thread", number, "is changing the value to", value
print "Thread", number, "is releasing the lock."
lock.release()
else:
print "Thread", number, "tried to write to the value, but could not."
def Threadwrite(number):
global value
while True:
if lock.acquire(False):
print "Thread", number ,"four says that the value is", value
else:
print "Thread", number ,"tried to read the value, but could not."
if __name__ == "__main__":
for n in range(0,len(thread_readers)):
th =Thread(target=Threadread, args=(thread_readers[n],))
th.start()
for n in range(0,len(thread_writer)):
th =Thread(target=Threadwrite, args=(thread_writer[n],))
th.start()

Separate user interaction and computation.

Allow your program to accept user interaction while conducting a long running computation.

Example:

Hello user! Please input a string to permute: (input thread)
abcdef
Passing on abcdef... (input thread)
Please input another string to permute: (input thread)
lol
Passing on lol... (input thread)
Done Work On abcdef! (worker thread)
["abcdef", "abcefd", ... ] (worker thread)
Please input another string to permute: (input thread)
EXIT
Quitting, I

'll let my worker thread know... (input thread)

We'

re quitting! Alright! (worker thread)

--Notice, that this could be accomplished on the command line or within a GUI. The point is that computation and user interaction should take place on separate threads of control.

java

public class BackgroundComputation {

final protected Queue<Thread> threads = new ConcurrentLinkedQueue<Thread>() ;

public BackgroundComputation() {
BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
try {
while (true) {
System.out.print("Enter string to permutate: ");
final String word = r.readLine();
if ("EXIT".equals(word) ) {
System.out.println("I'll let my worker thread know... (input thread)") ;
while (! threads.isEmpty())
threads.poll().stop(new ThreadDeath()) ;
break ;
}
Thread t = new Thread(new Runnable() {
public void run() {
try {
Set<String> permutationSet = new HashSet<String>();
for (int i = 0; i < word.length(); i++)
for (int j = i + 1; j <= word.length(); j++)
permutations("", word.substring(i, j), permutationSet);
System.out.println();
System.out.println("Received results: " + permutationSet);
System.out.print("Enter string to permutate: ");
} catch (ThreadDeath e) {
System.out.println("We're quitting! Alright!");
}
}

private void permutations(String prefix, String word, Set<String> permutations) {
int N = word.length();
if (N == 0)
permutations.add(prefix);
else
for (int i = 0; i < N; i++)
permutations(
prefix + word.charAt(i),
word.substring(0, i) + word.substring(i + 1, N),
permutations
);
}
});
t.start();
threads.add(t);
}
} catch (IOException ioe) {
System.out.println("IO error trying to read your name!");
System.exit(1);
}
}

public static void main(String[] args) {
new BackgroundComputation() ;
}
}

groovy

def threads = new ConcurrentLinkedQueue<Thread>()

void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}

println 'Welcome to the parallel permuter'
System.in.withReader { r ->
while (true) {
print 'Enter word:'
def word = r.readLine()
if (word == 'EXIT') {
while (!threads.isEmpty())
threads.poll().stop(new ThreadDeath())
break
} else
threads << Thread.start {
try {
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
println '\nAnswer:' + wordAns
print 'Enter word:'
} catch (ThreadDeath td) {
println 'Thread aborted!'
}
}
}
}