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Solved Problems

Strings

Printing

Output a string to the console

Write the string "Hello World!" to STDOUT

clojure

(println "Hello World!")

cpp

std::cout << "Hello World" << std::endl;

std::printf("Hello World\n");

Console::WriteLine(L"Hello World");

csharp

System.Console.WriteLine("Hello World!")

erlang

io:format("Hello, World!~n").

fantom

echo("Hello World!")

fsharp

printfn "Hello World!"

groovy

println "Hello World!"

haskell

main = putStrLn "Hello World!"

java

System.out.println("Hello World!");

System.out.printf("Hello World!\n");

ocaml

print_string "Hello world!\n";;

print_endline "Hello world!";;

Printf.printf "Hello world!\n";;

perl

print "Hello World!\n"

python

print "Hello World!"

ruby

puts "Hello World!"

$stdout<<"Hello World!"

scala

println("Hello World!")

printf("Hello World!\n")

Declaration

Define a string containing special characters

Define the literal string "\#{'}${"}/"

clojure

(def special "\\#{'}${\"}/")

cpp

std::string special = "\\#{'}${\"}/";

String^ special = L"\\#{'}${\"}/";

csharp

string verbatim = @"\#{'}${""""}/";
string cStyle = "\\#{'}${\"\"}/";

erlang

Special = "\\#{'}\${\"}/",

fantom

special := Str<|\#{'}${"}/|>

fsharp

let special = "\#{'}${\"}/"

groovy

special = "\\#{'}\${\"}/"

special = '\\#{\'}${"}/'

special = /\#{'}${'$'}{"}\//

haskell

putStrLn "\"\\#{'}${\"}/\""

let special = "\\#{'}${\"}/"

java

String special = "\\#{'}${\"}/";

ocaml

"\\#{'}${\"}/"

perl

$special = '\#{\'}${"}/';

$special = q(\#{'}${"}/);

python

# yes, Python has way too many forms of string literals :)
print "\\#{'}${\"}/"
print "\\#{'}${"'"'"}/"
print r"""\#{'}${"}/"""
print '\\#{\'}${"}/'
print '\\#{'"'"'}${"}/'
print r'''\#{'}${"}/'''

ruby

special = '\#{\'}${"}/'

scala

val special = "\\#{'}${\"}/"
val special2 = """\#{'}${"}/"""

Define a multiline string

Define the string:

"This

Is

A

Multiline

String"

clojure

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

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";

csharp

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

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

erlang

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

fantom

s := "This
Is
A
Multiline
String"

fsharp

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

let multiline = "This
Is
A
Multiline
String"

groovy

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

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

haskell

s = "This \
\Is \
\A \
\Multiline \
\String"

java

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

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

ocaml

"This\nIs\nA\nMultiline\nString"

"This
Is
A
Multiline
String"

perl

$text = 'This
Is
A
Multiline
String';

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

python

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

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

ruby

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

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

scala

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

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

Define a string containing variables and expressions

Given variables a=3 and b=4 output "3+4=7"

clojure

(format "%d + %d = %d" a b (+ a b))

cpp

Console::WriteLine(L"{0}+{1}={2}", a, b, a+b);

std::printf("%d+%d=%d\n", a, b, a+b);

std::cout << boost::format("%|1|+%|1|=%|1|") % a % b % (a+b) << std::endl;

csharp

int a = 3;
int b = 4;
Console.WriteLine("{0}+{1}={2}", a,b,a+b);

erlang

A = 3, B = 4,
io:format("~B+~B=~B~n", [A, B, (A+B)]).

fantom

echo("$a+$b=${a+b}")

fsharp

let a, b = 3, 4
let mystr = sprintf "%d+%d=%d" a b (a+b)
printfn "%s" mystr

groovy

println "$a+$b=${a+b}"

printf "%d+%d=%d\n", a, b, a + b

haskell

import Text.Printf

main = do
let a = 3
let b = 4
printf "%d+%d=%d" a b (a + b)

a = 3
b = 4
s = show a ++ "+" ++ show b ++ "=" ++ show (a + b)
main = putStrLn s

java

System.out.println(a + "+" + b + "=" + (a+b));

System.out.printf("%d+%d=%d\n", a, b, a + b);

ocaml

Printf.printf "%d+%d=%d" a b (a+b);;

perl

print "$a+$b=${\($a+$b)}\n";

sprintf("%d+%d=%d", $a, $b, $a + $b);

print $a, '+', $b, '=', $a + $b;

python

class EvalDict(dict):
def __getitem__(s, k):
return eval(k, s)

a=3; b=4
"%(a)d+%(b)d=%(a+b)d" % EvalDict(locals())

a=3; b=4
"%d+%d=%d" % (a, b, a+b)

ruby

puts "#{a}+#{b}=#{a+b}"

puts "#{a}+#{b}=%s" % (a + b)

scala

printf("%d+%d=%d\n", a, b, a + b)

"%d+%d=%d".format(a, b, a + b)

s"$a + $b = ${a+b}"

Manipulation

Reverse the characters in a string

Given the string "reverse me", produce the string "em esrever"

clojure

(require '[clojure.contrib.str-utils2 :as str])
(str/reverse "reverse me")

(apply str (reverse "reverse me"))

cpp

String^ s = "reverse me";
array<Char>^ sa = s->ToCharArray();
Array::Reverse(sa);
String^ sr = gcnew String(sa);

std::string s = "reverse me";
std::reverse(s.begin(), s.end());

std::string s = "reverse me";
std::string sr(s.rbegin(), s.rend());

std::string s = "reverse me";
std::swap_ranges(s.begin(), (s.begin() + s.size() / 2), s.rbegin());

csharp

var str = "reverse me";
Console.WriteLine(new String(str.Reverse().ToArray()));

erlang

Reversed = lists:reverse("reverse me"),

Reversed = revchars("reverse me"),

fantom

"reverse me".reverse

fsharp

let reversed = new String (Array.rev ("reverse me".ToCharArray()))

let word = "reverse me"
//reverse the word
let reversedword =
word.ToCharArray()
|> Array.fold(fun acc x -> x::acc) []

groovy

reversed = "reverse me".reverse()

haskell

reverse "reverse me"

java

String reverse = new StringBuffer("reverse me").reverse().toString();

String reverse = new StringBuilder("reverse me").reverse().toString();

String reverse = StringUtils.reverse("reverse me");

ocaml

let reverse str =
let len = String.length str in
let res = String.create len in
for i = 0 to pred len do
let j = pred len - i in
res.[i] <- str.[j]
done;
(res)

let rev_char str =
let l = Str.split (Str.regexp "") str in
List.fold_left (fun a b -> b ^ a) "" l
;;

perl

$_ = reverse "reverse me"; print

python

"reverse me"[::-1]

ruby

puts "reverse me".reverse

scala

val reversed = "reverse me".reverse

Reverse the words in a string

Given the string "This is a end, my only friend!", produce the string "friend! only my end, the is This"

clojure

(require '[clojure.contrib.str-utils2 :as str])
(str/join " " (reverse (str/split "this is the end, my only friend!" #" ")))

(apply str (interpose " " (reverse (re-seq #"[^\s]+" "This is the end, my only friend!"))))

cpp

array<Char>^ sep = {L' '};
array<String^>^ words =
String(L"This is the end, my only friend!").Split(sep, StringSplitOptions::RemoveEmptyEntries);

Array::Reverse(words); String^ newwords = String::Join(L" ", words);

std::string words = "This is the end, my only friend!"; std::vector<std::string> swv;

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

csharp

var str = "This is a end, my only friend!";
str = String.Join(" ", str.Split().Reverse().ToArray());
Console.WriteLine(str);

erlang

Reversed = string:join(lists:reverse(string:tokens("This is the end, my only friend!", " ")), " "),

fantom

"This is a end, my only friend!".split.reverse.join(" ")

fsharp

let reversed = String.Join(" ", Array.rev("This is the end, my only friend!".Split [|' '|]))

groovy

reversed = "This is the end, my only friend!".split().reverse().join(' ')

reversed = "This is the end, my only friend!".tokenize(' ').reverse().join(' ')

def revdelim(c, s) { StringUtils.reverseDelimited(s, c) }
revwords = this.&revdelim.curry(" " as char)
reversed = revwords("This is the end, my only friend!")

reversed = StringUtils.reverseDelimited("This is the end, my only friend!", " " as char)

haskell

unwords (reverse (words "This is the end, my only friend!"))

java

List list = new ArrayList();
StringTokenizer st = new StringTokenizer(text, " ");
while(st.hasMoreTokens()) {
list.add(0, st.nextToken());
}
StringBuffer sb = new StringBuffer();
for (Iterator iterator = list.iterator(); iterator.hasNext();) {
String word = (String) iterator.next();
sb.append(word);
if (iterator.hasNext()) {
sb.append(" ");
}
}
String reversed = sb.toString();

List<String> ls = Arrays.asList("This is the end, my only friend!".split("\\s"));
Collections.reverse(ls);
StringBuilder sb = new StringBuilder(32); for (String s : ls) sb.append(" ").append(s);
String reversed = sb.toString().trim();

String reversed = StringUtils.reverseDelimited("This is the end, my only friend!", ' ');

ocaml

let rev_words str =
let l = Str.split (Str.regexp " ") str in
String.concat " " (List.rev l)
;;

perl

$reversed = join ' ', reverse split / /, $text;

python

' '.join(reversed("This is a end, my only friend!".split()))

ruby

reversed = text.split.reverse.join(' ')

scala

"This is the end, my only friend!".split(" ").reverse.reduceLeft( (x,y) => x+' '+y )

val reversed = revwords("This is the end, my only friend!")

(("This is the end, my only friend!" split " ") reverse) mkString " "

val reversedText = text.split(" ").reverse.mkString(" ")

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.

clojure

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

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);

void rep(ostream &os, const string& str, int times)
{
while (times--)
os << str;
}

void wrap(ostream &os, const string& str, const string &prefix, int width)
{
int line_len = width;
bool first_word = true;

width -= prefix.size();
BOOST_FOREACH(string word, tokenizer<char_separator<char>>(str, char_separator<char>(" ")))
{
line_len += word.size();
if (line_len++ < width)
os << ' ';
else {
if (first_word)
first_word = false;
else
os << endl;
os << prefix;
line_len = word.size();
}
os << word;
}
os << endl;
}

int main()
{
stringstream input;

rep(input, "The quick brown fox jumps over the lazy dog. ", 10);
wrap(cout, input.str(), "> ", 72);
}

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));
}
}

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")).

fantom

buf := Buf()
10.times { buf.writeChars("The quick brown fox jumps over the lazy dog. ") }
buf.flip

out := Env.cur.out
sep := ">"; max := 72 - sep.size - 1
acc := 0; Str? s := null
while ((s = buf.readStrToken) != null)
{
if (acc == 0)
out.print(sep)

acc += s.size
if (acc > max)
{
out.print("\n$sep")
acc = s.size
}
out.print(" $s")
buf.readStrToken(4096) { !it.isSpace }
acc++
}

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)

let output maxWidth (s: string) =
let rec wrap = function
| lineSoFar, ([| |]: string array)-> printfn "%s" lineSoFar
| ">" as lineSoFar, (words: string array) ->
// Handle this case separately, thus we can also deal with
// cases where a word is longer then the max width
wrap (lineSoFar + " " + words.[0], Array.sub words 1 (words.Length - 1))
| lineSoFar, words when words.[0].Length + lineSoFar.Length >= maxWidth ->
printfn "%s" lineSoFar
wrap (">", words)
| lineSoFar, words ->
wrap(lineSoFar + " " + words.[0], Array.sub words 1 (words.Length - 1))
wrap (">", s.Split([| ' ' |]))

[| for i in 1 .. 10 do yield "The quick brown fox jumps over the lazy dog." |]
|> String.concat " "
|> output 78

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 }

haskell

import Data.List (intercalate)

-- our list of words ["The", "quick", "brown", ...]
dogs = concat$ replicate 10$ words "The quick brown fox jumps over the lazy dog."

-- ["The", "The quick", "The quick brown", ...]
concats = scanl1 (\s v -> s ++ " " ++ v)

-- takes list of words, returns list of lines
wordwrap :: Int -> [String] -> [String]
wordwrap maxwidth [] = []
wordwrap maxwidth ws = sentence : (wordwrap maxwidth restwords)
where
zipped = zip (concats ws) ws
(sentences, rest) = span (\(s,w) -> (length s) <= maxwidth) zipped
sentence = last (map fst sentences)
restwords = map snd rest

main = putStrLn ("> " ++ intercalate "\n> " (wordwrap 76 dogs))

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);

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

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;

python

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

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")

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)}

def wrap(words: List[String]): List[List[String]] = words match {
case Nil => Nil
case _ =>
val output = (words.inits.dropWhile { _.mkString(" ").length > 78 }) next;
output :: wrap(words.drop(output.length))
}

wrap(("The quick brown fox jumps over the lazy dog. " * 10) split(" ") toList) foreach {
words => println("> " + words.mkString(" "))
}

Remove leading and trailing whitespace from a string

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

clojure

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

(clojure.string/trim " hello ")

(.trim " hello ")

cpp

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

csharp

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

erlang

Trimmed = string:strip(S),

fantom

s := " hello ".trim

fsharp

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

let trimmed = " hello ".Trim()

groovy

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

haskell

unwords (words " hello ")

java

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

ocaml

let left_pos s len =
let rec aux i =
if i >= len then None
else match s.[i] with
| ' ' | '\n' | '\t' | '\r' -> aux (succ i)
| _ -> Some i
in
aux 0

let right_pos s len =
let rec aux i =
if i < 0 then None
else match s.[i] with
| ' ' | '\n' | '\t' | '\r' -> aux (pred i)
| _ -> Some i
in
aux (pred len)

let trim s =
let len = String.length s in
match left_pos s len, right_pos s len with
| Some i, Some j -> String.sub s i (j - i + 1)
| None, None -> ""
| _ -> assert false

let () =
let res = trim " hello " in
print_endline res

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

python

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

ruby

puts " hello ".strip

" hello ".strip!

scala

val s = " hello ".trim

Case

Make a string uppercase

Transform "Space Monkey" into "SPACE MONKEY"

clojure

(.toUpperCase "Space Monkey")

cpp

String(L"Space Monkey").ToUpper();

std::string s = "Space Monkey";
std::transform(s.begin(), s.end(), s.begin(), std::toupper);

std::string s = "Space Monkey";
boost::to_upper(s);

csharp

string output = "Space Monkey"

System.Console.WriteLine(output.ToUpper())

erlang

io:format("~s~n", [string:to_upper("Space Monkey")]).

fantom

s := "Space Monkey".localeUpper

fsharp

printfn "%s" ("Space Monkey".ToUpper())

printfn "%s" (String.uppercase "Space Monkey")

groovy

println "Space Monkey".toUpperCase()

haskell

toUpperCase oldstring converted = if oldstring == ""
then converted
else toUpperCase (tail(oldstring)) (converted ++ [Char.toUpper(head(oldstring))])

toUpperCase "Space Monkey" ""

toUpperCase = map Char.toUpper

toUpperCase "Space Monkey"

java

String upper = text.toUpperCase();

ocaml

String.uppercase "Space Monkey";;

perl

print uc "Space Monkey"

python

"Space Monkey".upper()

ruby

uppper = text.upcase

scala

println("Space Monkey".toUpperCase)

Make a string lowercase

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

clojure

(.toLowerCase "Caps ARE overRated")

cpp

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

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

csharp

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

erlang

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

fantom

s := "Caps ARE overRated".localeLower

fsharp

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

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

groovy

println "Caps ARE overRated".toLowerCase()

haskell

import Char
str = map toLower "Caps ARE overRated"

java

"Caps ARE overRated".toLowerCase();

ocaml

String.lowercase "Caps ARE overRated";;

perl

print lc "Caps ARE overRated"

python

"Caps ARE overRated".lower()

ruby

"Caps ARE overRated".downcase

scala

"Caps ARE overRated".toLowerCase

Capitalise the first letter of each word

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

clojure

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

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();

csharp

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

erlang

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

fantom

"man OF stEEL".split.map { it.localeLower.localeCapitalize }.join(" ")

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))

// Previous solutions used old library functions, here's something that works with F# 2.0
let s= "man OF stEEL"
let UpperFirst = function | "" -> "" | s -> s.Substring(0,1).ToUpper() + s.Substring(1).ToLower()
s.Split(' ') |> Array.map UpperFirst |> String.concat " "

let culture = System.Globalization.CultureInfo.GetCultureInfo("en-US")
let titleCase = culture.TextInfo.ToTitleCase "man oF sTeel"

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")

haskell

import Data.Char

capitalizeWords = unwords . map capitalizeWord . words
where capitalizeWord [] = []
capitalizeWord (c:cs) = toUpper c : map toLower cs

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");

ocaml

let capitalize_words str =
let len = String.length str in
let res = String.copy str in
let rec aux i do_up =
if i >= len then res else
match str.[i] with
| ' ' | '\n' | '\t' | '\r' -> aux (succ i) true
| _ ->
res.[i] <-
(if do_up then Char.uppercase else Char.lowercase) str.[i];
aux (succ i) false
in
aux 0 true

let () =
print_endline (capitalize_words "man OF stEEL")

perl

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

python

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

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

"man OF stEEL".title()

ruby

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

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

text.split.map(&:capitalize) * ' '

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(" ")

// This is just a slightly more compact form of the previous solution (my fav).
// It would be nice if split defaulted to whitespace (precompiled reg ex).
"man OF stEEL".toLowerCase.split(" ").map(_.capitalize) mkString " "

Numbers

Mathematical

Find the distance between two points

clojure

(defstruct point :x :y)

(defn distance
"Euclidean distance between 2 points"
[p1 p2]
(Math/pow (+ (Math/pow (- (:x p1) (:x p2)) 2)
(Math/pow (- (:y p1) (:y p2)) 2))
0.5))

(distance (struct point 0 0) (struct point 1 1)) ; => 1.4142135623730951

(defn distance
"Euclidean distance between 2 points"
[[x1 y1] [x2 y2]]
(Math/sqrt
(+ (Math/pow (- x1 x2) 2)
(Math/pow (- y1 y2) 2))))

(distance [2 2] [3 3])

cpp

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

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)));

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]).

fantom

px1 := 34.0f; py1 := 78.0f; px2 := 67.0f; py2 := -45.0f
distance := |Float x1, Float y1, Float x2, Float y2 -> Float|
{ ((x2-x1).pow(2.0f) + (y2-y1).pow(2.0f)).sqrt }

distance(px1, py1, px2, py2)

fsharp

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

groovy

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

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

haskell

data Floating n => Point2 n = Point2 n n

distance :: Floating n => Point2 n -> Point2 n -> n
distance (Point2 x1 y1) (Point2 x2 y2) = sqrt (x'*x' + y'*y')
where
x' = x1 - x2
y' = y1 - y2

-- > distance (Point2 5 10) (Point2 3 5)
-- 5.385...
-- > distance (Point2 1 1) (Point2 2 2)
-- 1.414...

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);

double distance = Math.hypot(x2-x1, y2-y1);

ocaml

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

perl

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

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)))

from math import hypot
print hypot(x2-x1, y2-y1)

ruby

# the hypotenuse sqrt(x**2+y**2)
distance = Math.hypot(x2-x1,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)))

def euclideanDistance(point1: List[Double], point2: List[Double]): Double = {
sqrt(point1.zip(point2).foldLeft(0.0){case(sum,(v1,v2)) => sum + pow(v1-v2, 2)})
}

Output

Zero pad a number

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

clojure

(defn pad
([x] (if (> 8 (.length (str x))) (pad (str 0 x)) (str x)))
)

(defn pad [x]
(format "%08d" x))

(format "%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;

csharp

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

erlang

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

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

fantom

formatted := 42.toStr.padl(8, '0')

formatted := 42.toLocale("00000000")

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)

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)

haskell

import Text.Printf

printf "%08d" 42

java

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

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

ocaml

Printf.printf "%08d" 42;;

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

perl

sprintf("%08d", 42);

python

"%08d" % 42

ruby

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

"%08d" % 42

scala

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

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

println("%08d".format(42))

Right Space pad a number

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

clojure

(let [s (str 1024)
l (count s)]
(str s (reduce str (repeat (- 6 l) " "))))

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;

csharp

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

erlang

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

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

fantom

formatted := 1024.toStr.padr(6)

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)

groovy

println 1024.toString().padRight(6)

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

haskell

let s = show 1024
p = 6
in s ++ (replicate (p - length s) ' ')

import Text.Printf

main = do
putStrLn $ printf "%-6d" (1024::Int)

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);

ocaml

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

perl

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

python

"%-6s" % 1024

str(1024).rjust(6)

'{0: <6}'.format(1024)

ruby

1024.to_s.ljust(6)

scala

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

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

println("%-6d".format(1024))

Format a decimal number

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

clojure

(format "%3.2f" (/ 7.0 8))

(* 0.01 (Math/round (* 100 (float (/ 7 8)))))

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;

csharp

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

erlang

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

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

fantom

formatted := (7.0/8.0).toLocale("0.00")

fsharp

printfn "%3.2f" (0.7 / 0.8)

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

groovy

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

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

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

haskell

import Text.Printf

printf "%3.2f" (7/8)

main = putStrLn $ Numeric.showFFloat (Just 2) (7/8) ""

java

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

ocaml

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

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

perl

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

python

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

round(7./8., 2)

ruby

(7.0/8.0*100).round/100.0

(7.0/8.0).round(2)

scala

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

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

Left Space pad a number

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

clojure

(let [s (str 73)
l (count s)]
(str (reduce str (repeat (- 10 l) " ")) s ))

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;

csharp

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

erlang

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

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

fantom

formatted := 73.toStr.padl(10)

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)

groovy

println 73.toString().padLeft(10)

printf "%10d\n", 73

haskell

import Text.Printf

formatted :: String
formatted = printf "%10d" 73

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);

ocaml

Printf.printf "%10d" 73;;

perl

sprintf("%10d", 73);

python

"%10s" % 73

ruby

73.to_s.rjust(10)

scala

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

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

Random

Generate a random integer in a given range

Produce a random integer between 100 and 200 inclusive

clojure

(+ (rand-int (- 201 100)) 100)

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();

csharp

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

erlang

RandomInt = gen_rand_integer(100, 200),

fantom

r := Int.random(100..200)

fsharp

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

groovy

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

haskell

import System.Random

randInRange :: Int -> Int -> IO Int
randInRange a b = getStdRandom $ randomR (a, b)

main = randInRange 100 200 >>= print

import System.Random

main = randomRIO (1,100) >>= print

java

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

ocaml

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

perl

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

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

print "$random_number\n";

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)

ruby

randomInt = rand(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)))

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.

clojure

(dotimes [_ 2]
(let [r (java.util.Random. 12345)]
(dotimes [_ 5]
(println (.nextInt r 100))))
(println))

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);

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());
}
}

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))]).

fantom

rand := Random.makeSeeded(12345)
first := Int[,].fill(0,5).map { rand.next(100..200) }

rand2 := Random.makeSeeded(12345)
second := Int[,].fill(0,5).map { rand2.next(100..200) }

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 ""

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

haskell

import System.Random
import Control.Monad (forM_)

main = do
printRands
printRands

where printRands = forM_ [1..5] (\i -> print (randInt i))
randInt i = fst $ randomR (100, 200) (mkStdGen i) :: Int

import System.Random

gen1 = mkStdGen 12345
gen2 = mkStdGen 12345

main = do
print $ take 5 (randoms gen1 :: [Float])
print $ take 5 (randoms gen2 :: [Float])

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(); }

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);;

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";

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)

ruby

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

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()

Regex

Matching

Check if a string matches a regular expression

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

clojure

(if (re-matches #"[A-Z][a-z]+" "Hello")
(println "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");

cmatch what;
if (regex_match("Hello", what, regex("[A-Z][a-z]+")))
cout << "ok" << endl;

csharp

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

fantom

if (Regex<|[A-Z][a-z]+|>.matches("Hello"))
echo("ok")

fsharp

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

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'

haskell

import Text.Regex.Posix
main = if "Hello" =~ "[A-Z][a-z]+" then putStrLn "OK" else return ()

java

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

ocaml

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

perl

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

python

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

ruby

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

scala

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

Check if a string matches with groups

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

clojure

(if-let [groups (re-matches #"one (.*) three" "one two three")]
(println (second groups)))

cpp

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

cmatch what;
if (regex_match("one two three", what, regex("one (.*) three")))
cout << what[1] << endl;

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]);
}
}

erlang

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

fantom

m := Regex<|one (.*) three|>.matcher("one two three")
if (m.matches)
echo("${m.group(1)}")

fsharp

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

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

haskell

import Text.Regex
main = case matchRegex (mkRegex "one (.*) three") "one two three" of
Nothing -> return ()
Just (x:_) -> putStrLn x

java

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

ocaml

#load "str.cma" ;;

let s = "one two three" in
if Str.string_match (Str.regexp "one \$.*\$ three") s 0 then
print_string (Str.matched_group 1 s)

perl

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

python

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

ruby

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

scala

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

Searching

Check if a string contains a match to a regular expression

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

clojure

(if (re-find #"\d+" "abc 123 @#$")
(println "ok"))

cpp

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

csharp

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

fantom

m := Regex<|\d+|>.matcher("abc 123 @#\$")
if (m.find)
echo("ok")

fsharp

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

groovy

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

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

haskell

import Text.Regex
main = case matchRegex (mkRegex "\d+") "abc 123 @#$" of
Nothing -> putStrLn "not ok"
Just _ -> putStrLn "ok"

java

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

ocaml

#load "str.cma" ;;

let re = Str.regexp "[0-9]+" in
try let _ = Str.search_forward re "abc 123 @#$" 0 in
print_string "ok"
with _ -> ()

perl

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

python

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

ruby

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

scala

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

clojure

(let [matcher (re-matcher #"$(\w+)$:(\d+)" "(fish):1 sausage (cow):3 tree (boat):4")]
(loop [match (re-find matcher)
lst []]
(if match
(recur (re-find matcher) (conj lst (str (second match) (nth match 2))))
lst)))

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();
}

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;});
}
}

erlang

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

fantom

m := Regex<|$(\w+)$:(\d+)|>.matcher(s)
list := Str[,]
while (m.find) { list.add("${m.group(1)}${m.group(2)}") }

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

// A solution without mutation:
let results =
Regex.Matches("(fish):1 sausage (cow):3 tree (boat):4", "\$(\\w+)\$:(\\d+)")
|> Seq.cast
|> Seq.map (fun (regmatch: Match) ->
regmatch.Groups.[1].Captures.[0].ToString() + regmatch.Groups.[2].Captures.[0].ToString()
)
|> List.ofSeq

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] }

haskell

import Text.Regex

getParenNum s = case matchRegexAll re s of
Nothing -> []
Just (_,_,after,[word,num]) -> (word ++ num):getParenNum after where
re = mkRegex "\$(\\w+)\$:([[:digit:]]+)"

main = putStrLn (show (getParenNum "(fish):1 sausage (cow):3 tree (boat):4"))

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));
}

ocaml

let result =
let str = "(fish):1 sausage (cow):3 tree (boat):4" in
let ms = Pcre.exec_all ~pat:"\$(\\w+)\$:(\\d+)" str in
Array.to_list (
Array.map (fun m ->
let s = Pcre.get_substrings m in
Printf.sprintf "%s%s" s.(1) s.(2);
) ms
)

perl

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

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"))

ruby

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

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

Lists

Declaration

Define an empty list

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

clojure

(list)

'()

cpp

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

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

csharp

var list = new List<object>();

erlang

List = [],

fantom

list := [,]

fsharp

let list = []

let list = List.empty

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

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

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

haskell

let list = []

java

List list = Collections.emptyList();

String[] list = {};

ocaml

let list = [];;

perl

@list = ();

python

list = []

ruby

list = []

list = Array.new

scala

val list = Nil

val list = List()

val list : List[String] = List()

Define a static list

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

clojure

(def a '[One Two Three Four Five])

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");

list<string> lst = { "One", "Two", "Three", "Four", "Five" };

list<string> lst;
lst += "One", "Two", "Three", "Four", "Five";

csharp

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

erlang

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

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

fantom

list := ["One", "Two", "Three", "Four", "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))

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+

haskell

let a = ["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"); }};

ocaml

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

perl

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

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

python

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

ruby

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

list = %w(One Two Three Four Five)

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")

Output

Join the elements of a list, separated by commas

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

clojure

(apply str (interpose ", " '("Apple" "Banana" "Carrot")))

cpp

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

string fruits[] = {"Apple", "Banana", "Carrot"};
string result = boost::algorithm::join(fruits, ", ");

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()) );
}
}

erlang

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

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

Result = lists:flatten([ hd(Fruit) | [ ", " ++ X || X <- tl(Fruit)]]).

fantom

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

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()

groovy

string = fruit.join(', ')

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

haskell

import Data.List

let join = intercalate ", " ["Apple", "Banana", "Carrot"]

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, ", ");

ocaml

let () =
let lst = ["Apple"; "Banana"; "Carrot"] in
let str = String.concat ", " lst in
print_endline str

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";

my @a = qw/Apple Banana Carrot/;
{
local $, = ", ";
print @a
}
print "\n";

my @a = qw/Apple Banana Carrot/;
{
local $" = ", ";
print "@a\n";
}

python

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

ruby

string = fruit.join(', ')

scala

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

val result = fruit.mkString(",")

val fruit = List[String]("Apple", "Banana", "Carrot")
println(fruit.mkString(", "))

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([]) = ""

clojure

(defn join [lst]
(cond
(= (count lst) 0) ""
(= (count lst) 1) (first lst)
(= (count lst) 2) (str (first lst) " and " (second lst))
(> (count lst) 2) (loop [lst lst sb (StringBuilder.)]
(if (empty? lst)
(.toString sb)
(recur (rest lst) (.append sb (cond
(> (count lst) 2) (str (first lst) ", ")
(> (count lst) 1) (str (first lst) ", and ")
(= (count lst) 1) (str (first lst)))))))))

(defn join
([lst]
(join lst false))
([lst is-long]
(condp = (count lst)
0 ""
1 (first lst)
2 (str (first lst) (if is-long ",") " and " (second lst))
(str (first lst) ", " (join (rest lst) true)))))

cpp

Console::WriteLine(join(fruit));

string join(const vector<string> &s, int b=0)
{
switch (s.size() - b)
{
case 0: return "";
case 1: return s[b];
case 2: return s[b] + (s.size() > 2 ? "," : "") + " and " + s[b+1];
default: return s[b] + ", " + join(s, b+1);
}
}

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>()) );
}
}

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).

%% According to the reference manual, "string is not a data type in Erlang."
%% Instead it has lists of integers. But I/O functions in general accept
%% IO lists, where an IO list is either a list of IO lists or an integer.
%% This gives you O(1) string concatenation.

-module(commalist).
-export([join/1]).

join([]) -> "";
join([W]) -> W;
join([W1, W2]) -> [W1, " and ", W2];
join([W1, W2, W3]) -> [W1, ", ", W2, ", and ", W3];
join([W1|Ws]) -> [W1, ", ", join(Ws)].

fantom

join := |List list -> Str|
{
switch(list.size)
{
case 0: return ""
case 1: return list[0]
case 2: return list.join(" and ")
default: return list[0..-2].join(", ") + ", and " + list[-1]
}
}

echo(join(["Apple", "Banana", "Carrot"]))
echo(join(["One", "Two"]))
echo(join(["Lonely"]))
echo(join([,]))

fsharp

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]
}
}

ArrayList.metaClass.joinEng = { ->
def closureMap = [0: { -> delegate.join(' and ')}, 1 : {-> delegate.join(' and ')}].withDefault { k -> { -> delegate[0..-2].join(', ') + ', and ' + delegate[-1] } }
if (delegate.size()) closureMap[delegate.size()-1].call()
else ""
}

assert ["a"].joinEng() == "a"
assert ["a", "b"].joinEng() == "a and b"
assert ["a", "b", "c"].joinEng() == "a, b, and c"
assert [].joinEng() == ""

haskell

join [] = ""
join [x] = x
join [x,y] = x ++ " and " ++ y
join [x,y,z] = x ++ ", " ++ y ++ ", and " ++ z
join (x:xs) = x ++ ", " ++ join xs

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));

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 ""

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);
}

# Yes, this doesn't meet the spec, the spec is flawed
# the serial comma (Oxford comma) is not required in a list
sub english_join {
return join(', ', @_[0..$#_-1])
. ($#_ ? ' and ' : '' )
. $_[-1];
}

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(*[]) == ""

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

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)
}

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 x::xs => x + ", " + join(xs)
}

def join[T](list : List[T]) = list match {
case xs if xs.size < 3 => xs.mkString(" and ")
case xs => xs.init.mkString(", ") + ", and " + xs.last
}

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]]

clojure

(defn combine [lst1 lst2]
(mapcat (fn [x] (map #(list % x) lst1)) lst2))

(mapcat (fn [x] (map #(list % x) ["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));

string letters[] = { "a", "b", "c" };
int numbers[] = { 4, 5 };
list<pair<string,int> > combo;

for (int n = 0; n < sizeof numbers / sizeof *numbers; n++)
for (int l = 0; l < sizeof letters / sizeof *letters; l++)
combo.push_back(make_pair(letters[l], numbers[n]));

cout << combo << endl;

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 });
}
}
}
}

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]].

fantom

[4,5].each |Int i| { ["a","b","c"].each |Str s| { r.add([i,s]) } }

fsharp

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

let combinations aa bb =
aa
|> List.map (fun a -> bb |> List.map (fun b -> (a, b)))
|> List.concat

groovy

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

haskell

comb :: [(String, Int)]
comb = do
b <- [4,5]
a <- ["a","b","c"]
return (a,b)

main = mapM_ print comb

comb :: [(String, Int)]
comb = [(a, b) | b <- [4,5], a <- ["a","b","c"]]

main = print comb

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)));

ocaml

let combinations =
let l1 = ["a"; "b"; "c"]
and l2 = [4; 5] in
List.rev (
List.fold_left (fun acc y ->
List.fold_left (fun acc2 x ->
(x, y)::acc2
) acc l1
) [] l2
)

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];
}
}

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])]

ruby

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

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)

From a List Produce a List of Duplicate Entries

Taking a list:
["andrew", "bob", "chris", "bob"]

Write the code to produce a list of duplicates in the list:
["bob"]

clojure

(->> '("andrew" "bob" "chris" "bob")
(group-by identity)
(filter #(> (count (second %)) 1))
(map first))

cpp

vector<string> lst = { "andrew", "bob", "chris", "bob" };
vector<string> lst_no_dups;
vector<string> tmp;
vector<string> dups;

sort(lst.begin(), lst.end());
unique_copy(lst.begin(), lst.end(), back_inserter(lst_no_dups));
set_difference(lst.begin(), lst.end(),
lst_no_dups.begin(), lst_no_dups.end(),
back_inserter(tmp));
unique_copy(tmp.begin(), tmp.end(), back_inserter(dups));

cout << dups << endl;

list<string> lst = { "andrew", "bob", "chris", "bob" };
map<string,int> num_identical;
list<string> dups;

for (auto &s: lst)
num_identical[s]++;
for (auto &n: num_identical)
if (n.second > 1)
dups.push_back(n.first);
cout << dups << endl;

csharp

List<String> values = new List<string> {"andrew", "bob", "chris", "bob"};

var duplicates = values
.GroupBy(i => i)
.Where(j => j.Count() > 1)
.Select(s => s.Key);
foreach (var duplicate in duplicates)
{
Console.WriteLine(duplicate);
}

erlang

{_, Result} = lists:foldl(
fun(X, {Uniq, Dupl}) -> case lists:member(X, Uniq) of
true -> {Uniq,[X | Dupl]};
_ -> {[X | Uniq], Dupl}
end
end,
{[], []},
List),

Fun = fun
([X | Xs], F) -> case lists:member(X, Xs) of
true -> [X | F(Xs, F)];
_ -> F(Xs, F)
end;
([], _) -> []
end,
Result = Fun(List, Fun).

fantom

nameCounts := Str:Int[:] { def = 0 }
["andrew", "bob", "chris", "bob"].each |Str v| { nameCounts[v]++ }
results := nameCounts.findAll |Int v, Str k->Bool| { v > 1 }.keys
echo(results.join(","))

fsharp

["andrew"; "bob"; "chris"; "bob"]
|> Seq.countBy id
|> Seq.filter (fun (k,n) -> n > 1)
|> Seq.map fst
|> Seq.toList

groovy

def input = ["andrew", "bob", "chris", "bob"]

def output = input.findAll{input.count(it)>1}.unique()

assert output == ["bob"]

haskell

import Data.List

input = ["andrew", "bob", "chris", "bob"]
output = [ head l | l <- group (sort input), length l > 1]

java

List listOfDuplicates = new ArrayList(Arrays.asList(new String[]{"andrew", "bob", "chris", "bob"}));

Set set = new HashSet(listOfDuplicates);
for (Object element : set)
listOfDuplicates.remove(element);

ocaml

let rem v lst =
let rec aux acc = function
| [] -> List.rev acc
| x::xs ->
if compare v x = 0
then aux acc xs
else aux (x::acc) xs
in
aux [] lst

(** in case of a match, returns a list with the duplicate(s) removed *)
let rec mem_rem v lst =
let rec aux acc = function
| [] -> None
| x::xs ->
if compare v x = 0
then Some(List.rev_append acc (rem v xs))
else aux (x::acc) xs
in
aux [] lst

let duplicates lst =
let rec aux acc = function
| [] -> List.rev acc
| x::xs ->
match mem_rem x xs with
| Some ret -> aux (x::acc) ret
| None -> aux acc xs
in
aux [] lst

let () =
let lst = ["andrew"; "bob"; "chris"; "bob"; "mike"; "peter"; "bob"] in
let dup = duplicates lst in
List.iter print_endline dup

(* Using standard (functorized) sets *)

module SetTools(ASet: Set.S) =
struct
let find_duplicates l =
let rec aux l seen acc =
match l with
| [] -> acc
| h :: q ->
if ASet.mem h seen then
aux q seen (h :: acc)
else
aux q (ASet.add h seen) acc in
aux l (ASet.empty) []
end

module StringSet = Set.Make(String)

module StringSetTools = SetTools(StringSet)

StringSetTools.find_duplicates ["andrew"; "bob"; "chris"; "bob"];;

perl

my @input = ("andrew", "bob", "chris", "bob", "bob");

my %input_count;
my @output = grep { $input_count{$_}++; $input_count{$_} == 2 } @input;

python

import itertools
input = ["andrew", "bob", "chris", "bob"]
input.sort()
output = [k for k, g in itertools.groupby(input, lambda x: x) if len(list(g)) > 1]

ruby

foo = ['andrew', 'bob', 'chris', 'bob']
foo.inject({}) {|h,v| h[v]=h[v].to_i+1; h}.reject{|k,v| v==1}.keys

scala

List("andrew", "bob", "chris", "bob")
.groupBy(identity)
.filter( person => person._2.size > 1)
.map(_._1)

val l = List("andrew", "bob", "chris", "bob")
l.diff(l.distinct)

Access

Fetch an element of a list by index

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

clojure

(nth '[One Two Three Four Five] 2)

cpp

String^ result = list[2];

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

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),

fantom

["One", "Two", "Three", "Four", "Five"][2]

["One", "Two", "Three", "Four", "Five"].get(2)

fsharp

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

groovy

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

haskell

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

java

String result = list.get(2);

ocaml

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

perl

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

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

python

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

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

scala

val result = list(2)

Fetch the last element of a list

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

clojure

(last '[One Two Three Four Five])

cpp

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

string last_elem = lst.back();

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"

erlang

Result = lists:last(List),

Result = last(List),

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

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

fantom

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

["One", "Two", "Three", "Four", "Five"].last

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))

groovy

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

haskell

last ["Red", "Green", "Blue"]

java

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

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);;

let list_last l =
let rec aux h q =
match q with
| [] -> h
| h :: q -> aux h q in
match l with
| [] -> invalid_arg "list_last"
| h :: q -> aux h q
;;
list_last ["Red"; "Green"; "Blue"]

perl

qw(Red Green Blue)[-1];

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

python

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

ruby

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

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

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

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

scala

val result = list.last

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

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?

clojure

(use 'clojure.set)

(let [beans '[broad mung black red white]
colors '[black red blue green]]
(intersection (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);

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']

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)),

fantom

beans := ["broad", "mung", "black", "red", "white"]
colors := ["black", "red", "blue", "green"]
echo(beans.intersection(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)

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

// Iterates elements of
// list1 across Elements of list2 returning a list of string options
// as generated by List.tryFind
let findCommon(list1 : 'a list, list2 : 'a list) : 'a list =
list1 |> List.map(fun y -> list2 |> List.tryFind(fun x -> y = x))
// Iterates elements of string option list generated above
// returning a string list containing common elements of List1 and List2
|> List.fold(fun acc x -> if x <> None then x.Value::acc else acc) []
// reverse order of list (can't seem to make List.foldBack work for this
|> List.rev

let beans = ["broad"; "mung"; "black"; "red"; "white"]
let colors = ["black"; "red"; "blue"; "green"]
printfn "%A" (findCommon(beans, colors)) ;;

groovy

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

haskell

import Data.List

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

main = print (intersect beans colors)

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);

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 *)

(* using standard (functorized) sets *)

module SetTools(ASet: Set.S) =
struct
let of_list l =
List.fold_left (fun acc e -> ASet.add e acc) ASet.empty l

let find_common l1 l2 =
ASet.elements (ASet.inter (of_list l1) (of_list l2))
end

module StringSet = Set.Make(String)

module StringSetTools = SetTools(StringSet)
;;
let beans = ["broad"; "mung"; "black"; "red"; "white"] in
let colors = ["black"; "red"; "blue"; "green"] in
StringSetTools.find_common 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);

@beans = qw(broad mung black red white);
@colors = qw(black red blue green);

my %colors_hash = map { $_ => 1 } @colors;
my @intersection = grep { $colors_hash{$_} } @beans;
print join(', ', @intersection),"\n";

@beans = qw/broad mung black red white/;
@colors = qw/black red blue green/;

print join ', ', grep { $_ ~~ @colors } @beans;

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)

ruby

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

scala

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

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.

clojure

;; returns a set
(set [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;#{14 16 17 18 19}

;; returns a lazy sequence of the unique elements
(distinct [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;(18 16 17 19 14)

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);

list<int> input;
input += 18, 16, 17, 18, 16, 19, 14, 17, 19, 18;
input.sort();
unique_copy(input.begin(), input.end(), ostream_iterator<int>(cout, "\n"));

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();
}
}

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]).

fantom

uniqueAges := [18, 16, 17, 18, 16, 19, 14, 17, 19, 18].unique
echo(uniqueAges)

fsharp

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

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

haskell

import Data.List

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

uniqueAges = nub 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);

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;;

(* using standard (functorized) sets *)

module SetTools(ASet: Set.S) =
struct
let of_list l =
List.fold_left (fun acc e -> ASet.add e acc) ASet.empty l

let unique l =
ASet.elements (of_list l)
end

module Integer =
struct
type t = int
let compare (x:t) y = Pervasives.compare x y
end

module IntegerSet = Set.Make(Integer)
module IntegerSetTools = SetTools(IntegerSet)
;;
IntegerSetTools.unique [18; 16; 17; 18; 16; 19; 14; 17; 19; 18];;

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));

python

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

unique_ages = list(set(ages))

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

scala

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

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]

clojure

(let [fruit ["Apple" "Banana" "Carrot"]
index 0]
(concat
(take index fruit)
(drop (+ index 1) fruit)))

cpp

fruit->RemoveAt(0);

csharp

class Solution1516
{
static void Main()
{
List<string> fruit = new List<string>() { "Apple", "Banana", "Carrot" };
fruit.RemoveAt(0);
}
}

erlang

Result = tl(List),

[_|Result] = List,

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

Result = drop(1, List),

fantom

list := ["Apple", "Banana", "Carrot"]
list.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)

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)

haskell

deleteNth n xs | n > 0 = take (n-1) xs ++ drop n xs

main = print $ deleteNth 1 [1..3]

fruit :: [String]
fruit = ["Apple", "Banana", "Carrot"]

main :: IO ()
main = putStrLn $ show $ tail fruit

java

list.remove(0);

ocaml

let delete_at i al =
if i < 0 || i >= List.length al then
invalid_arg "delete_at"
else
let rec del i l =
match l with
| [] -> []
| h::t when i = 0 -> t
| h::t -> h :: del (i-1) t
in
del i al
;;

let rem_first l =
match l with
| [] -> []
| h::t -> t
;;

List.tl ["Apple"; "Banana"; "Carrot"]

perl

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

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

python

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

ruby

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

fruit.delete_at(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)

Remove the last element of a list

clojure

(pop ["Apple" "Banana" "Carrot"])

cpp

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

csharp

List<string> fruits = new List() { "apple", "banana", "cherry" };
fruits.RemoveAt(fruits.Length - 1);

erlang

Result = init(List),

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

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

fantom

list := ["Apple", "Banana", "Carrot"]
list.removeAt(-1)

list := ["Apple", "Banana", "Carrot"]¨
list.pop

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)

groovy

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

haskell

ages = [1,2,3,4]

init ages

java

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

ocaml

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

let remove_last lst =
List.rev (List.tl (List.rev lst))

let list_remove_last l =
let rec aux h q acc =
match q with
| [] -> List.rev acc
| h2 :: q -> aux h2 q (h :: acc) in
match l with
| [] -> invalid_arg "list_remove_last"
| h :: q -> aux h q []

perl

pop @list;

python

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

ruby

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

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

scala

fruit = fruit.init

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

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"]

clojure

(let [fruit ["apple" "orange" "grapes" "bananas"]]
(concat (rest fruit) [(first fruit)])

cpp

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

rotate(fruit.begin(), fruit.begin()+1, fruit.end());

csharp

var lst = new LinkedList<String>(new String[] {"apple", "orange", "grapes", "banana"});
lst.AddLast(lst.First());
lst.DeleteFirst();

erlang

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

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

fantom

list := ["apple", "orange", "grapes", "bananas"]
list.add(list.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)

groovy

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

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

items = items + items.remove(0)

haskell

main = print $ rotate ["apple", "orange", "grapes", "bananas"]

rotate xs | length xs < 2 = xs
| otherwise = tail xs ++ [head xs]

java

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

Collections.rotate(list, -1);

ocaml

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

perl

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

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

python

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

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

ruby

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

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

scala

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

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

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.

clojure

(defn gatherer [listOfLists]
(if (empty? (first listOfLists))
() ; the base case for recursion
(cons
(map first listOfLists) ; get the first element of each of the lists
(gatherer (map rest listOfLists)) ; gather all the subsequent ones
)
)
)

(def firstnames '("Bruce" "Tommy Lee" "Bruce"))
(def lastnames '("Willis" "Jones" "Lee"))
(def years '(1955 1946 1940))

(println (gatherer [firstnames lastnames years]))

; -> ((Bruce Willis 1955) (Tommy Lee Jones 1946) (Bruce Lee 1940))

(def firstnames ["Bruce" "Tommy Lee" "Bruce"])
(def lastnames ["Willis" "Jones" "Lee"])
(def years [1955 1946 1940])
(println (map (fn [f l y] [f l y]) firstnames lastnames years))

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);

list<string> first = { "Bruce", "Tommy Lee", "Bruce" };
list<string> last = {"Willis", "Jones", "Lee"};
list<int> years = {1955, 1946, 1940};
list<tuple<string,string,int> > actors;

for (firstIt = first.begin(), lastIt = last.begin(), yearIt = years.begin();
firstIt != first.end() && lastIt != last.end() && yearIt != years.end();
++firstIt, ++lastIt, ++yearIt)
actors.push_back(make_tuple(*firstIt, *lastIt, *yearIt));

csharp

String[] first = { "Bruce", "Tommy Lee", "Bruce" };
String[] last = { "Willis", "Jones", "Lee" };
int[] years = { 1955, 1946, 1940 };
var actors = first.Zip(last, (f, l) => Tuple.Create(f, l)).Zip(years, (t, y) => Tuple.Create(t.Item1, t.Item2, y)).ToArray();
Debug.Assert(actors[1].Equals(Tuple.Create("Tommy Lee", "Jones", 1946)));

erlang

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

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

fantom

r := [,]
first.size.times |Int i| { r.add([first[i], last[i], years[i]]) }

echo(r)

fsharp

let result = (List.zip3 first last years)

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]

haskell

import Prelude hiding (last)

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

actors = zip3 first 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);

ocaml

let rec combine3 f l y =
match f, l, y with
| [], [], [] -> []
| fh :: fq, lh :: lq, yh :: yq ->
(fh, lh, yh) :: combine3 fq lq yq
| _ -> invalid_arg "combine3"
;;
let first = ["Bruce"; "Tommy Lee"; "Bruce"] in
let last = ["Willis"; "Jones"; "Lee"] in
let years = [1955; 1946; 1940] in
combine3 first last years

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] ];
};

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)

ruby

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

result = first.zip(last, years)

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

result = [first, last, years].transpose

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)

val first = List("Bruce", "Tommy Lee", "Bruce")
val last = List("Willis", "Jones", "Lee")
val years = List(1955, 1946, 1940)
val results = (first, last, years).zipped.toList
println(results)

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'.

clojure

(def suites ["H" "D" "C" "S"])
(def faces [2 3 4 5 6 7 8 9 10 "J" "Q" "K" "A"])
(defn listCards [] (for [s suites f faces] [f s]))
(some (partial = ["A" "H"]) (listCards))
; -> true
(count (listCards))
; -> 52

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");

auto suites = {"h", "d", "c", "s"};
auto faces = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};
list<card> cards;

for (auto s: suites)
for (auto f: faces)
cards.push_back(make_pair(s,f));

cout << "Deck has " << cards.size() << " cards." << endl;

card ace_of_harts = make_pair("h", "A");
if (end(cards) != find_if(begin(cards), end(cards),
[&](const card& c) { return c == ace_of_harts; }))
cout << "Deck contain 'Ace of Harts'" << endl;
else
cout << "Deck lacks 'Ace of Harts'" << endl;

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();
}
}
}

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).

fantom

r := [,]
["2","3","4","5","6","7","8","9","10","J","Q","K","A"].each |Str c|
{ ["H","D","C","S"].each |Str s| { r.add([c,s]) } }

q := ["A","H"]
result := r.contains(q)
echo("Deck size=${r.size}, contains $q? -> $result")

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")

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

haskell

import Data.List

suites = ["H", "D", "C", "S"]
faces = ["2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"]

main = do
let cards = [(s,f) | s <- suites, f <- faces ]
print (length cards)
print $ hasCard ("H", "A") "Ace of Hearts" cards
where hasCard t name cards = (if elem t cards then "Contains "
else "Does not contain") ++ name

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");

ocaml

let suites = ["H"; "D"; "C"; "S"]
let faces = ["2";"3";"4";"5";"6";"7";"8";"9";"10";"J";"Q";"K";"A"]

let desk =
List.fold_left (fun acc y ->
List.fold_left (fun acc2 x ->
(x, y)::acc2
) acc faces
) [] suites

let () =
assert (List.length desk = 52);
if List.mem ("A", "H") desk
then print_endline "Ace of Hearts found!"
else print_endline "Ace of Hearts not found :("

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";

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

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

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")

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]

clojure

(map count ["ox" "cat" "deer" "whale"])

cpp

list<string> words;

words.push_back("ox");
words.push_back("cat");
words.push_back("deer");
words.push_back("whale");

for (list<string>::iterator it = words.begin(); it != words.end(); ++it)
cout << it->size() << ' ';
cout << endl;

auto words = { "ox", "cat", "deer", "whale" };
list<size_t> word_sizes;

transform(begin(words),
end(words),
back_inserter(word_sizes),
[](const string& s) { return s.size(); });

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 );
}
}

erlang

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

fantom

["ox", "cat", "deer", "whale"].map { it.size }

fsharp

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

groovy

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

haskell

map length ["ox", "cat", "deer", "whale"]

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() + " ");
}
}
}

ocaml

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

perl

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

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

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

python

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

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

ruby

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

scala

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

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.

clojure

(def jumble [3 "Bill" 5.7 '("A" "B" "C")]) ; int, string, float, list

(defn numberNonNumberSorter [jumbledList]
(if (empty? jumbledList)
(hash-map :numbers [], :nonnumbers []) ; recursion base case - return two empty lists
(let [head (first jumbledList)] ; let <head> be the first element in the list
(let [tailresult (numberNonNumberSorter (rest jumbledList))] ; tailresult applies recursively to the remainder
(if (number? head) ; is head a number?
(hash-map
:numbers (cons head (tailresult :numbers)) ; add <head> to the numbers
:nonnumbers (tailresult :nonnumbers)) ; leave nonnumbers the same
(hash-map
:numbers (tailresult :numbers) ; leave numbers the same
:nonnumbers (cons head (tailresult :nonnumbers))) ; add <head> to nonnumbers
)
)
)
)
)

(println (numberNonNumberSorter jumble))

; -> {:nonnumbers (Bill (A B C)), :numbers (3 5.7)}

(group-by number? ["hello" 42 3.14 (Date.)])

cpp

typedef variant<int,float,string,date> dynamic;

class is_number : public static_visitor<bool>
{
public:
bool operator()(int &) const {
return true;
}
bool operator()(float &) const {
return true;
}
bool operator()(string &) const {
return false;
}
bool operator()(date &) const {
return false;
}
};

int main()
{
list<dynamic> lst;
list<dynamic> numbers;
list<dynamic> non_numbers;

lst += "hello", 3.14f, 42, date(2011,Aug,23);

BOOST_FOREACH(dynamic v, lst)
if (apply_visitor(is_number(), v))
numbers += v;
else
non_numbers += v;

#include <iostream>
#include <list>

#include <boost/any.hpp>
#include <boost/date_time/gregorian/gregorian.hpp>
#include <boost/foreach.hpp>

using namespace boost;
using namespace boost::gregorian;
using namespace std;

int main()
{
list<any> lst;
list<any> numbers;
list<any> non_numbers;

lst.push_back(string("hello"));
lst.push_back(42);
lst.push_back(3.14f);
lst.push_back(date(day_clock::local_day()));

BOOST_FOREACH(const any &a, lst)
try
{
numbers.push_back(any_cast<int>(a));
}
catch (bad_any_cast &e)
{
try
{
numbers.push_back(any_cast<float>(a));
}
catch (bad_any_cast &e)
{
non_numbers.push_back(a);
}
}

// float and int are now in 'numbers' and the rest in 'non_numbers'
}

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) );
}

}

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)

fantom

things := ["hello", 25, 3.14, Time.now]
numbers := things.findType(Num#)
nonNumbers := things.exclude { numbers.contains(it) }

fsharp

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]

haskell

import Data.List (partition)

type Date = String
data Things = TS String | TI Int | TD Date
deriving Show

main = do
let myList = [TI 1, TI 23, TS "Joe", TD "23/04/2009"]
print $ partition isNumber myList

where isNumber (TS _) = False
isNumber (TI _) = True
isNumber (TD _) = False

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) ;
}
}

ocaml

(* OCaml is a strongly statically typed language so it is not possible to mix
items of different types in a single list.
So here we use a list of strings, some of these strings represent a number *)

let is_a_number v =
try ignore(float_of_string v); true
with _ -> false

let numbers, others =
List.partition is_a_number ["Joe"; "3.14"; "8"; "hello"; "23/04/2009"]

(* ========================================================================== *)
(* If we really want to mix items of several types, we can declare a variant: *)

type item = Int of int | Float of float | String of string | Char of char

let is_a_number = function
| Float _ | Int _ -> true
| String _ | Char _ -> false

let numbers, others =
List.partition is_a_number [String "Joe"; Float 3.14; Int 8; Char 'Z']

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, $_;
}
}

python

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

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

ruby

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

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

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

numbers, others=things.partition{|i| i.is_a? Numeric}

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)))

Maps

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

clojure

(let [l '[a b a c b b]]
(loop [m {}
d (distinct l)]
(let [item (first d)]
(if (zero? (count d))
m
(recur
(assoc m
item
(count
(filter #(= item %) l)))
(rest d))))))

(->> [:a :b :a :c :b :b]
(group-by identity)
(reduce (fn [m e] (assoc m (first e) (count (second e)))) {}))

(reduce conj {} (for [[x xs] (group-by identity "abacbb")] [x (count xs)]))

(frequencies ["a","b","a","c","b","b"])

(frequencies '[a b a c b b])

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;

map<string,int> hist;
for (auto e: { "a","b","a","c","b","b" })
++hist[e];
for (auto e: hist)
cout << e.first << " : " << e.second << endl;

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()
)
);
}
}

new[] {"a","b","a","c","b","b"}
.GroupBy(s => s)
.Select(s => new { Value = s.Key, Count = s.Count() })
.ToList()
.ForEach(e => Console.WriteLine("{0} : {1} ", e.Value, e.Count));

erlang

% Imperative Solution
Histogram = histogram(List),

% Functional (1) Solution
Histogram = histogram(List),

lists:foldl(fun(Elem, OldDict) ->
dict:update_counter(Elem, 1, OldDict)
end,
dict:new(),
[a,b,a,c,b,b])).

fantom

list := ["a","b","a","c","b","b"]
map := [Str:Int][:]
list.each |Str s, Int i| { if(!map.containsKey(s)) map.add(s,1); else map[s] = ++map[s] }
echo (map)

fsharp

let histogram = (List.foldLeft (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.foldLeft (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)

let histogram =
list
|> Seq.groupBy (fun a -> a)
|> Seq.map(fun (key, elements) -> key, Seq.length elements)
|> Map.ofSeq

groovy

histogram = [:]
list.each { item ->
if (!histogram.containsKey(item)) histogram[item] = 0
histogram[item]++
}

histogram = [:]
list.each { histogram[it] = (histogram[it] ?: 0) + 1 }

haskell

import Data.List
import qualified Data.Map as Map

histogram :: Ord a => [a] -> Map.Map a Int
histogram xs = Map.fromList [ (head l, length l) | l <- group (sort xs) ]

output :: Map.Map String Int
output = histogram ["a","b","a","c","b","b"]

import Control.Arrow
import Data.List
import qualified Data.Map as Map
import System.Random

histogram :: Ord a => [a] -> Map.Map a Int
histogram = Map.fromList . map (head &&& length) . group . sort

main = print . histogram . take 1000 . randomRs (1::Int, 100) =<< newStdGen

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);

ocaml

module StringMap = Map.Make (String)

let histogram lst =
List.fold_left (fun m v ->
let n =
if StringMap.mem v m
then succ (StringMap.find v m)
else 1
in
StringMap.add v n m
) StringMap.empty lst

let () =
let h = histogram ["a"; "b"; "a"; "c"; "b"; "b"] in
StringMap.iter (fun key value ->
Printf.printf " %s: %d\n" key value
) h

perl

foreach(@list) {
$histogram{$_}++;
}

$histogram{$_}++ for @list;

python

from collections import defaultdict
h = defaultdict(int)
for k in "abacbb":
h[k] += 1

h = {}
for k in "abacbb":
h[k] = h.setdefault(k, 0) + 1

from collections import Counter
h = Counter("abacbb")
print(h)

ruby

histogram = {}
list.each { |item| histogram[item] = (histogram[item] || 0) +1 }

list = %w{a b a c b b}

histogram = list.each_with_object(Hash.new(0)) do |item, hash|
hash[item] += 1
end

p histogram # => {"a"=>2, "b"=>3, "c"=>1}

list.inject(Hash.new(0)) {|h, item| h[item] += 1; h}

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))

val histEntries = for {
key <- data.removeDuplicates
count = data.count(_ == key)
} yield (key -> count)
val hist = Map(histEntries: _*)

value.foldLeft(Map[T, Int]()){
(m, c) => m.updated(c, m.getOrElse(c, 0) + 1)
}

list.groupBy(identity).mapValues(_.size)

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

clojure

(loop [m {}
l ["one" "two" "three" "four" "five"]]
(if (zero? (count l))
m
(let [item (first l)
key (count item)]
(recur
(assoc m key (cons item (get m key [])))
(rest l)))))

(group-by count ["one" "two" "three" "four" "five"])

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);
}

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
}
}

erlang

% Imperative Solution
CatList = categorise(List),

% Functional (1) Solution
CatList = categorise(List),

fantom

list := ["one", "two", "three", "four", "five"]
map := [Int:List][:]
list.each { List l := map[it.size] ?: [,]; map[it.size] = l.add(it) }
echo(map)

fsharp

let catmap = (List.foldLeft (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)

let lengthMap =
["one"; "two"; "three"; "four"; "five"]
|> Seq.groupBy (fun s -> s.Length)
|> Seq.map (fun (length, entries) -> (length, entries |> List.ofSeq))
|> Map.ofSeq

groovy

map = ['one', 'two', 'three', 'four', 'five'].groupBy{ it.size() }

haskell

import qualified Data.Map as Map

groupInMapBy :: Ord k => (a -> k) -> [a] -> Map.Map k [a]
groupInMapBy f = foldr (\a -> Map.insertWith (++) (f a) [a]) Map.empty

output :: Map.Map Int [String]
output = groupInMapBy length ["one", "two", "three", "four", "five"]

import Data.List (groupBy, sortBy)
import Data.Function (on)

groupInPairsBy :: Ord k => (a -> k) -> [a] -> [(k, [a])]
groupInPairsBy f = map (\xs -> (f (head xs), xs)) .
groupBy ((==) `on` f) . sortBy (compare `on` f)

output :: [(Int, [String])]
output = groupInPairsBy length ["one", "two", "three", "four", "five"]

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);

ocaml

let map =
List.fold_left (fun map v ->
let len = String.length v in
let before =
try IntMap.find len map
with Not_found -> [] in
IntMap.add len (v :: before) map
) IntMap.empty ["one"; "two"; "three"; "four"; "five"]

perl

@list = qw(one two three four five);
push @{$map{length($_)}}, $_ for (@list);

python

c = defaultdict(list)
for k in ["one", "two", "four", "three", "five"]:
c[len(k)].append(k)

from itertools import groupby
lst = ["one", "two", "four", "three", "five"]
c = dict((k, list(g)) for k,g in
groupby(sorted(lst, key=lambda x: len(x)), key=lambda x: len(x)))
print(c)

ruby

lengths = {}
list.each do |x|
len = x.size
lengths[len] = (lengths[len] || [])
lengths[len] << x
end

lengths = list.group_by {|x| x.size}

list.inject({}) { |h,x| (h[x.size]||=[]) << x; h }

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)

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.

clojure

(def person "Bob")
(if (= person "Bob")
(println "Hello, Bob!"))

cpp

if (name == "Bob") Console::WriteLine("Hello, {0}!", name);

if (name == "Bob") std::cout << "Hello, " << name << "!" << std::endl;

csharp

if (name == "Bob") Console.WriteLine("Hello, {0}!", name);

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).

fantom

if (name=="Bob") echo("Hello, Bob!")

fsharp

if name = "Bob" then printfn "Hello, %s!" name

name = "Bob" && begin printfn "Hello, %s!" name ; true end

groovy

if (name=='Bob')
println "Hello, Bob!"

haskell

name = "Bob"
main = if name == "Bob" then putStrLn "Hello, Bob!" else return ()

java

if (name.equals("Bob")) {
System.out.println("Hello, Bob!");
}

ocaml

if name = "Bob"
then print_string "Hello, Bob!"

perl

if ($name eq "Bob") {
print "Hello, Bob!"
}

print "Hello, Bob!" if $name eq "Bob";

python

if name == 'Bob':
print 'Hello, Bob!'

ruby

if (name=='Bob')
puts "Hello, Bob!"
end

puts "Hello, Bob!" if name=='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)

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"

clojure

(def age 41)
(if (> age 42) "You are old" "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"));

csharp

int age = 41;

if (age > 42)

System.Console.WriteLine("You are old");
else
System.Console.WriteLine("You are young");

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).

(fun (X) when X > 42 -> io:format("You are old~n"); (_) -> io:format("You are young~n") end)(Age).

(fun () when Age > 42 -> io:format("You are old~n"); () -> io:format("You are young~n") end)().

io:format("You are ~s~n", [if Age > 42 -> "old" ; true -> "young" end]).

fantom

if (age > 42)
echo("You are old")
else
echo("You are young")

echo((age > 42) ? "You are old" : "You are 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

groovy

if (age > 42)
println "You are old"
else
println "You are young"

println "You are " + (age > 42 ? "old" : "young")

haskell

putStrLn ("You are " ++ if age > 42 then "old" else "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"));

ocaml

if age > 42
then print_string "You are old"
else print_string "You are young"

perl

if ($age > 42) {
print "You are old"
}
else {
print "You are young"
}

print 'You are ',($age > 42) ? 'old' : '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'

ruby

if (age > 42)
puts "You are old"
else
puts "You are young"
end

puts (age>42) ? "You are old" : "You are young"

puts "You are #{age > 42 ? "old" : "young"}"

scala

val age = 42
if (age > 42) println("You are old") else println("You are young")

println( "You are " + ( if ( age > 42 ) "old" else "young" ) )

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

clojure

(def n 112)

(println (str n
(let [rem (mod n 100)]
(if (and (>= rem 11) (<= rem 13))
"th"
(condp = (mod n 10)
1 "st"
2 "nd"
3 "rd"
"th")))))

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();
}

csharp

public static string GetOrdinal(int i)
{
if (i > 10 && i < 20) return i.ToString() + "th";
switch (i % 10)
{
case 1:
return i.ToString() + "st";
case 2:
return i.ToString() + "nd";
case 3:
return i.ToString() + "rd";
default:
return i.ToString() + "th";
}
}

public static string GetOrdinal(int i)
{
if (i > 10 && i < 20) return i.ToString() + "th";
switch (i % 10)
{
case 1:
return i.ToString() + "st";
break;
case 2:
return i.ToString() + "nd";
break;
case 3:
return i.ToString() + "rd";
break;
default:
return i.ToString() + "th";
break;
}
}

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])

fantom

suffix := |Int n -> Str|
{
if ((4..20).contains(n % 100))
return "th"

switch((n.toStr)[-1])
{
case '1': return "st"
case '2': return "nd"
case '3': return "rd"
default: return "th"
}
}

(1..40).each { echo("$it${suffix(it)}") }

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))

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)}"
}

haskell

suffixed n = show n ++ suffix
where
suffix
| n `mod` 100 `div` 10 == 1 = "th"
| otherwise = case n `mod` 10 of
1 -> "st"
2 -> "nd"
3 -> "rd"
_ -> "th"

result = map suffixed [1..40]

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";
}
}

ocaml

let numsuffix i =
match i with
| 11 | 12 | 13 -> "th"
| x when x mod 10 = 1 -> "st"
| x when x mod 10 = 2 -> "nd"
| x when x mod 10 = 3 -> "rd"
| _ -> "th"
;;
(* alternate implementation without using guards:
let numsuffix i =
match i with
| 11 | 12 | 13 -> "th"
| x -> match x mod 10 with
| 1 -> "st"
| 2 -> "nd"
| 3 -> "rd"
| _ -> "th"
*)

for i = 1 to 40 do
Printf.printf "%d%s " i (numsuffix i);
done;
print_newline ()

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";
}

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)]

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) }

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))
}

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.

clojure

(take-while #(< % 150) (iterate #(* 2 %) 1))

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;

csharp

int x = 1;

while (x < 150)
{
x *= 2;
Console.Write("{0},", x);
}

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).

fantom

x := 1
while (x < 150) {
Env.cur.out.print("$x,")
x *= 2
}
echo

fsharp

let mutable x = 1
while x < 150 do printf "%d, " x ; (x <- x * 2) done

// The problem is clearly geared towards imperative languages ;-)
// No need to mutate any variable, here's how to do it loop-free functional:
let rec powers2 i = seq { if i < 150 then yield i; yield! powers2 (i*2) }
powers2 1 |> Seq.iter (fun i -> printf "%i, " i)

groovy

x = 1
while (x < 150) {
print x + ","
x *= 2
}
println()

haskell

main :: IO ()
main = loop 1
where
loop x | x < 150 = do
putStr (show x ++ ",")
loop (x * 2)
loop _ = return ()

main = mapM_ print $ takeWhile (<150) $ iterate (* 2) 1

java

int x = 1;
while (x < 150) {
System.out.println(x+",");
x*=2;
}

ocaml

let x = ref 1 ;;

while !x < 150 do
Printf.printf "%d," !x;
x := !x * 2;
done;

print_newline()

perl

my $x = 1;
while($x < 150) {
print $x, ",";
$x *=2
}

python

x = 1
while x < 150:
print '%s, ' % x,
x *= 2

ruby

x=1
while x < 150
puts x
x <<= 1
end

scala

var x = 1 ; while (x < 150) { printf("%d,", x) ; x *= 2 }

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"

clojure

(loop [r (rand-int 6)]
(if (= r 5)
nil
(do
(println r)
(recur (rand-int 6)))))

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();

csharp

System.Random die = new System.Random();
int roll;

do
{
roll = die.Next(1, 6);
Console.Write(roll);
if (roll < 6) Console.Write(",");
}
while (roll != 6);

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).

fantom

rnd := 0
while(rnd != 6) {
rnd = Int.random(1..6)
Env.cur.out.print(rnd)
if (rnd != 6)
Env.cur.out.print(",")
}
echo

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

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 ','
}

haskell

import System.Random

diceRolls = do
gen <- newStdGen
print $ takeWhile (/=(6::Int)) (randomRs (1,6) gen)

java

int rnd;
do {
rnd = (int)(Math.random()*6)+1;
System.out.print(rnd);
if (rnd!=6) {
System.out.print(",");
}
} while(rnd!=6);

ocaml

let () =
Random.self_init ();
let rec loop () =
let n = (Random.int 6) + 1 in
print_int n;
if n <> 6 then (print_char ','; loop ())
else print_newline ()
in
loop ()

perl

do {
my $number = int(rand(6)+1);
print $number;
print ',' if ($number != 6);
} while ($number != 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()))

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

begin
rnd = rand(6)+1
print rnd
print "," if rnd!=6
end while rnd != 6

# This uses Enumerators, ad it becomes almost functional style...

games = Enumerator.new do |yielder|
yielder.yield rand(6) + 1 while true
end

puts games.take_while {|roll| roll != 6}.join(",")

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)

Perform an action a fixed number of times (FOR)

Display the string "Hello" five times like "HelloHelloHelloHelloHello"

clojure

(dotimes [_ 5]
(print "Hello"))

cpp

for(int i = 0; i < 5; ++i) Console::Write("Hello");

for(int i = 5; i > 0; --i) Console::Write("Hello");

dotimes(5, hello);

fill_n(ostream_iterator<string>(cout), 5, "Hello");

csharp

string text = "Hello";

for (int i = 0; i < 5; i++)
{
Console.Write(text);
}

erlang

dotimes(5, fun () -> io:format("Hello") end).

lists:foreach(fun (_) -> io:format("Hello") end, lists:seq(1, 5)).

fantom

5.times { Env.cur.out.print("Hello") }

for (i := 0; i < 5; i++)
Env.cur.out.print("Hello")

(1..5).each { Env.cur.out.print("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

groovy

println "Hello" * 5

5.times { print "Hello" }; println()

haskell

import Control.Monad

hi5 = replicateM_ 5 $ putStr "Hello"

java

for(int i=0;i<5;i++) {
System.out.print("Hello");
}

ocaml

let rec write_hello = function
0 -> ()
| n ->
print_string "Hello" ;
write_hello (n-1)
;;
write_hello 5;;

let write_hello n =
for i = 1 to n do
print_string "Hello";
done

let () = write_hello 5

perl

print "Hello" x 5

print "Hello" for (1..5)

python

print "Hello" * 5

for i in range(5):
print "Hello"

ruby

puts "Hello"*5

5.times { print "Hello" }

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") }

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!"

clojure

(dotimes [i 10]
(print (str (- 10 i) " .. ")))

(println "Liftoff!")

cpp

for(int i = 10; i != 0; --i) Console::Write("{0} .. ", i);
Console::WriteLine("Liftoff!");

csharp

for (int i = 10; i > 0; i--)
{
Console.Write("{0} .. ", i);
}

Console.WriteLine("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").

fantom

(10..1).each { Env.cur.out.print("$it .. ") }
Env.cur.out.print("Liftoff!")

for (i := 10; i >= 1; i--)
Env.cur.out.print("$i .. ")
Env.cur.out.print("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!"

groovy

10.downto(1) { print it + " .. " }
println "Liftoff!"

haskell

countDown = mapM_ printN [10,9..1] >> putStr "Liftoff!"
where printN n = putStr $ show n ++ " .. "

java

for(int i=10; i>=1; i--) {
System.out.print(i + " .. ");
}
System.out.print("Liftoff!");

ocaml

for i = 10 downto 1 do
Printf.printf "%d .. " i
done;
print_endline "Liftoff!"

perl

for (my $i = 10; $i > 0; $i--) {
print "$i .. ";
}
print "Liftoff!";

print "$_ .. " for reverse 1..10;
print "Liftoff!";

python

print " .. ".join(str(i) for i in range(10, 0, -1)), ".. liftoff!"

ruby

10.downto(1) { |n| print n, " .. " }
puts "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!")

Files

Reading

Read the contents of a file into a string

clojure

(slurp "/tmp/foobar")

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");

csharp

string contents = System.IO.File.ReadAllText("filename.txt");

erlang

Text = readfile("Solution607.erl"),

Text = readfile("Solution608.erl"),

fantom

contents := File(`file.text`).readAllStr

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")

groovy

contents = file.text

haskell

readFile "c:/tmp/myFile.txt"

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);
}

ocaml

let read_file f =
let ic = open_in f in
let n = in_channel_length ic in
let s = String.create n in
really_input ic s 0 n;
close_in ic;
(s)

let file_contents = read_file "file.txt"

perl

@file = read()

open(my $fh, '<', $path) or die "can't open $path: $!";
$string = do { local $/; <$fh> };
close $fh;

python

contents = open('myFile.txt', 'rt').read()

ruby

file = File.new("Solution108.rb")
whole_file = file.read

scala

val text = FileUtils.readFileToString(new File("Solution467.scala"))

val text = Source.fromFile("Solution1256.scala").mkString("")

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

clojure

(defn read-line-by-line [fn]
(reduce str (map (partial format "%d> %s\n")
(iterate inc 1)
(read-lines fn))))

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);

csharp

int counter = 0;

// If the file is large, you would want to buffer this instead of reading everything at once
foreach (string line in System.IO.File.ReadAllLines("filename.txt"))
{
Console.WriteLine("{0}> {1}", ++counter, 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).

fantom

File(`input.text`).readAllLines.each |Str s, Int i| { echo("${i+1}> $s") }

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)

groovy

int count = 0
file.eachLine { line ->
println "${++count} > $line"
}

file.eachLine { line, count ->
println "${++count} > $line"
}

haskell

import Data.List

prefixWithNumber str n = show n ++ "> " ++ str

numberStrings (x:xs) n = prefixWithNumber x n : (numberStrings xs (n+1))
numberStrings [] n = []

main = do
str <- readFile "prefix.hs"
putStrLn (intercalate "\n" (numberStrings (lines str) 1))

prefix n str = show n ++ "> " ++ str

main = readFile "prefix.hs" >>=
putStr . unlines . zipWith prefix [1..] . lines

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);
}

ocaml

let () =
let ic = open_in Sys.argv.(1) in
let i = ref 1 in
try
while true do
Printf.printf "%d> %s\n" !i (input_line ic);
incr i
done
with End_of_file ->
close_in ic

let input_line_opt ic =
try Some (input_line ic)
with End_of_file -> None

let () =
let ic = open_in Sys.argv.(1) in
let rec aux i =
match input_line_opt ic with
| Some line ->
Printf.printf "%d> %s\n" i line;
aux (succ i)
| None ->
close_in ic
in
aux 1

perl

open(my $fh, '<', $path) or die "can't open $path: $!";
$c = 1;
print $c++ . "> $_" for (<$fh>);
close $fh;

open my $fh, '<', $path or die "Can't open $path: $!";
while (<$fh>) {
print "$.> $_";
}

python

for no, line in enumerate(open(__file__)):
print "{0}> {1}".format(no+1, line.rstrip())

ruby

File.open("Solution103.rb").each_with_index { |line, count|
puts "#{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) }

Writing

Write a string to a file

clojure

(with-out-writer "output.txt" (println "Hello file!"))

cpp

IO::StreamWriter^ stream;

try
{
stream = gcnew IO::StreamWriter("test.txt", false);
stream->WriteLine("This line overwites file contents!");
}

csharp

System.IO.File.WriteAllText("filename.txt", "Some text to write to the file");

erlang

Line = "This line overwites file contents!\n",
{ok, IODevice} = file:open("test.txt", [write]), file:write(IODevice, Line), file:close(IODevice).

fantom

File(`out.txt`).out.writeChars("some text").flush

fsharp

let stream = new StreamWriter("test.txt", false)
stream.WriteLine("This line overwrites file contents!")

groovy

file.delete()
file << 'some text'

file.text = 'some text'

haskell

writeFile "filename" "stringe"

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!");
}

ocaml

try
let cout = open_out filename in
let co = Format.formatter_of_out_channel cout in
Format.fprintf co "%s\n" text_to_write;
close_out cout
with Sys_error _ as e ->
Format.printf "Cannot open file \"%s\": %s\n" filename (Printexc.to_string e)

perl

open(my $fh, '>', $path) or die "can't open $path: $!";
print $fh "This line overwites file contents!";
close $fh;

python

open('test.txt', 'wt').write('Hello World!')

ruby

File.new("a_file", "w") << "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()

Append to a file

clojure

(with-out-append-writer "output.txt" (println "This is appended to the file"))

cpp

IO::StreamWriter^ stream;

try
{
stream = gcnew IO::StreamWriter("test.txt", true);
stream->WriteLine("This line appended to file!");
}

csharp

System.IO.File.AppendAllText("filename.txt", "Some text to append to the file");

erlang

Line = "This line appended to file!\n",
{ok, IODevice} = file:open("test.txt", [append]), file:write(IODevice, Line), file:close(IODevice).

fantom

File(`out.txt`).out(true).writeChars("some text").flush

fsharp

let stream = new StreamWriter("test.txt", true)
stream.WriteLine("This line appended to file!")

groovy

file << 'some text'

haskell

appendfile "filename" "string"

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!");
}

ocaml

let () =
let oc =
open_out_gen
[Open_wronly; Open_creat; Open_append; Open_text] 0o666 "test.txt" in
output_string oc "This line appended to file!\n";
close_out oc

perl

open(my $fh, '>>', $path) or die "can't open $path: $!";
print $fh "This line is appended to the file!";
close $fh;

python

open('test.txt', 'at').write('Hello World!\n')

ruby

file = File.new('/tmp/test.txt', 'a+') ; file.puts 'This line appended to file!!' ; file.close()

scala

val fw = new FileWriter("test.txt", true) ; fw.write("This line appended to file!") ; fw.close()

Directories

Process each file in a directory

clojure

; (defn process-file [f] "process one file" body...)
(map process-file (.listFiles (File. ".")))

cpp

for each(String^ filename in IO::Directory::GetFiles(dirname)) process(filename);

csharp

foreach (string filename in System.IO.Directory.GetFiles(directory)) ProcessFile(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)).

fantom

File(`./`).list.each { process(it) }

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)

groovy

dir.eachFile{ f -> process(f) }

haskell

import System.Directory
import Control.Monad

process filename = putStrLn filename

main = getDirectoryContents "." >>=
filterM doesFileExist >>=
mapM_ process

java

for (File file : (new File("c:\\")).listFiles()) process(file);

ocaml

let process dir file =
if not (Sys.is_directory (Filename.concat dir file))
then print_endline file

let () =
let dir = "." in
let files = Sys.readdir dir in
Array.iter (process dir) files

perl

use File::Glob;

for (<*>) {
process_file($_) if (-f);
}

python

import os
results = (process(f) for f in os.listdir(".") if os.path.isfile(f))

ruby

directory = '/tmp' ; Dir.foreach(directory) {|file| puts "#{file}"}

scala

for (file <- new File("c:\\").listFiles) { processFile(file) }

Dates

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.

clojure

(import 'java.util.Date)

(println (str (Date.)))

cpp

QDate now = QDate::currentData();
qDebug() << now.toString();

time_t date = time(0);
cout << ctime(&date);

csharp

// Creating a variable first:
DateTime now = DateTime.Now;
Console.WriteLine(now);

// Without creating a variable:
Console.WriteLine(DateTime.Now);

erlang

io:format("~p~n", [calendar:local_time()])

fantom

echo(DateTime.now)

fsharp

printfn "%A" System.DateTime.Now

groovy

println new Date()

haskell

import System.Time

main = do ct <- getClockTime
print ct

import Data.Time

main = do zt <- getZonedTime
print zt

java

import java.util.Date;

public class SolutionXX {
public static void main(String[] args) {
Date now = new Date();
System.out.println(now.toString());
}
}

ocaml

Unix.localtime (Unix.gettimeofday ())

perl

use Class::Date;
my $date = Class::Date->now();
print $date->string()."\n";

print localtime()."\n";

use Time::Piece ();

# Date object
my $date = Time::Piece::localtime;
print "$date\n";
# no object
print scalar(localtime),"\n";

python

from datetime import datetime
print datetime.utcnow()

ruby

puts DateTime.now

scala

println(new java.util.Date)

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.

clojure

(defprotocol IGreeter
(greet [this]))

(deftype Greeter [whom]
IGreeter
(greet [this]
(println (str "Hello, " whom))))

(greet (Greeter. "world"))

(defn greeter [whom]
{:whom whom})

(defn greet [g]
(println (str "Hello, " (:whom g))))

(greet (greeter "world"))

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);
}

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();
}
}

erlang

Greeter = make_greeter("world!"),
Greeter(greet).

fantom

class Greeter
{
private Str whom
new make(Str whom) { this.whom = whom }
Void greet() { echo("Hello, $whom") }
}

Greeter("world").greet

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()

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()

haskell

data Greeter = Greeter String

class Greets a where
greet :: a -> IO ()

instance Greets Greeter where
greet (Greeter s) = print s

main = greet (Greeter "Hello")

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();
}
}

ocaml

class greeter message =
object
method greet = print_endline message
end

let o = new greeter "Hello" in
o#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();

{
package Greeter;

sub new {
my $class = shift;
my $whom = shift or die 'Need a name to greet';
bless \$whom, $class;
}

sub greet {
my $self = shift;
print "Hello $$self!\n";
}
}

my $greeter = Greeter->new("Bob");
$greeter->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()

ruby

class Greeter
def initialize(whom) @whom = whom end
def greet() puts "Hello, #{@whom}!" end
end

(Greeter.new("world")).greet()

scala

class Greeter(whom : String) { def greet() = { printf("Hello %s\n", whom) } }

(new Greeter("world!")).greet()

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

clojure

(println (format "Total cost of items are $%#.2f"
(->> (xml-seq (parse *xml-input-stream*))
(filter #(= :item (:tag %))) ; Remove all but the item tags
(map :attrs) ; Keep the attributes
(map (fn [e] (str "(* " (:quantity e) " " (:price e) ")"))) ; Get the total price as a sexp
(map read-string) ; "(* quantity price)" -> (* quantity price)
(map eval) ; (* quantity price) -> quantity*price
(apply +)))) ; Sum all elements

cpp

char input[] =
"<shopping>"
" <item name=\"bread\" quantity=\"3\" price=\"2.50\"/>"
" <item name=\"milk\" quantity=\"2\" price=\"3.50\"/>"
"</shopping>";

xml_document<> doc;
doc.parse<0>(input);
xml_node<> *shopping = doc.first_node();

float total_price = 0;
for (xml_node<> *item = shopping->first_node(); item != NULL; item = item->next_sibling())
{
float item_sum = 0;
float val;

if (string(item->name()) != "item")
continue;

for (xml_attribute<> *attr = item->first_attribute(); attr != NULL; attr = attr->next_attribute())
{
string name(attr->name());
if (name == "quantity" || name == "price")
{
stringstream v(attr->value());
v >> val;
if (item_sum)
item_sum *= val;
else
item_sum = val;
}
}
total_price += item_sum;
}

cout.setf(ios::fixed, ios::floatfield);
cout << "Total price is $" << setprecision(2) << total_price << endl;

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);

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]).

fantom

sum := 0.0
root := XParser(File(`shop.xml`).in).parseDoc.root
if (root.name == "shopping")
{
root.elems.each
{
if (it.name == "item")
{
quantity := Int.fromStr(it.get("quantity"))
price := Decimal.fromStr(it.get("price"))
sum += quantity * price;
}
}
}
echo("\$$sum")

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

let xname sname = XName.Get sname
let xattr (elem: XElement) sname = elem.Attribute(xname sname).Value
let xml = XDocument.Load("xml.txt")

let shoppingCost =
xml.Descendants(xname "item")
|> Seq.map (fun i -> Double.Parse(xattr i "quantity"), Double.Parse(xattr i "price"))
|> Seq.sumBy (fun (quantity, price) -> quantity * price)

// Alternative solution that uses XML Navigation, and XPath expressions to ensure that
// the items have the required attributes
let xname sname = XName.Get sname
let xattr (elem: XElement) sname = elem.Attribute(xname sname).Value

let navigator = XPathDocument("xml.txt").CreateNavigator()
let path = XPathExpression.Compile("/shopping/item[@price][@quantity]")
let names = XmlNamespaceManager(navigator.NameTable)
path.SetContext(names)
let shoppingCost =
match path.ReturnType with
| XPathResultType.NodeSet ->
navigator.Select(path)
|> Seq.cast
|> Seq.map (fun (i: XPathNavigator) ->
if i.IsNode then
let elem = XElement.Parse(i.OuterXml)
Double.Parse(xattr elem "quantity"), Double.Parse(xattr elem "price")
else
failwith "Error in expression, expecting to see a node"
)
|> Seq.sumBy (fun (quantity, price) -> quantity * price)
| _ -> failwith "Error in expression, expecting to see a node set"

groovy

printf '$%.2f\n', new XmlSlurper().parseText(xml).item.collect{
it.@quantity.toInteger() * it.@price.toFloat()
}.sum()

haskell

File Edit Options Buffers Tools Haskell Help
import Text.ParserCombinators.Parsec
import Control.Monad
import System ( getArgs )

data Item = Item { name :: String,
quantity :: Int,
price :: Int }
deriving Show

type Basket = [Item]

item :: Parser Item
item = do string "<item name=\""
name <- manyTill letter (char '\"')
string " quantity=\""
quantity <- liftM read $ many digit
string "\" price=\""
dollars <- liftM read $ many digit
cents <- option 0 (char '.' >> (liftM read $ many digit))
string "\"/>"
return $ Item name quantity (100 * dollars + cents)

basket :: Parser Basket
basket = do string "<shopping>"
items <- manyTill item (try $ string "</shopping>")
return items

parseBasket :: String -> Basket
parseBasket input = case parse basket "Shopping Basket" input of
Left _ -> []
Right val -> val

main = do args <- getArgs
putStrLn $ show . (/100) . fromIntegral . sum . map (\(Item _ q p) -> q * p) . parseBasket $ head args

import Text.XML.HXT.Core
import Text.Printf

main :: IO ()
main = do
prices <- runX (process "basket.xml")
printf "$%.2f\n" $ sum prices

process :: FilePath -> IOSArrow XmlTree Double
process filename =
readDocument [withValidate no] filename >>>
getChildren >>>
isElem >>> hasName "shopping" >>>
getChildren >>>
isElem >>> hasName "item" >>>
getQuantity &&& getPrice >>>
arr (uncurry (*))

getQuantity :: IOSArrow XmlTree Double
getQuantity =
getAttrl >>> hasName "quantity" >>> getChildren >>>
getText >>> arr read

getPrice :: IOSArrow XmlTree Double
getPrice =
getAttrl >>> hasName "price" >>> getChildren >>>
getText >>> arr read

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();
}

ocaml

let () =
let xml = Xml.parse_file "shopping.xml" in
let res =
Xml.fold (fun total xml ->
match xml with
| Xml.Element ("item", attrs, _) ->
let quantity = float_of_string (List.assoc "quantity" attrs)
and price = float_of_string (List.assoc "price" attrs) in
total +. (quantity *. price)
| _ -> total
) 0.0 xml
in
Printf.printf "Total cost of the items: %g\n" res

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

use strict;
use XML::Twig;

use Data::Dumper;

my $xml = <<ENDXML;
<shopping>
<item name="bread" quantity="3" price="2.50"/>
<item name="milk" quantity="2" price="3.50"/>
</shopping>
ENDXML

my $xt = XML::Twig->parse( $xml );

my $price;
foreach my $item ($xt->root->children('item')) {
$price += ($item->{att}{price} * $item->{att}{quantity})
}

printf "Total Cost: %.2f\n", $price

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

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

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)

Algorithms

Arithmetic

Greatest Common Divisor

Find the largest positive integer that divides two given numbers without a remainder. For example, the GCD of 8 and 12 is 4.

clojure

(defn gcd [a b]
(if (zero? b)
a
(recur b (mod b a))))

cpp

#include <iostream>
#include <cstdlib>
#include <algorithm>

using namespace std;

int gcd_recursive(int i, int j) {
if (min(i, j) == 0)
return max(i, j);
else
return gcd_recursive(min(i, j), abs(i - j));
}

int gcd_recursive2(int x, int y) {
if (y == 0)
return x;
else
return gcd_recursive2(y, (x % y));
}

int gcd_iterative(int i, int j) {
while (min(i, j) != 0) {
i = min(i, j);
j = abs(i - j);
}
return max(i, j);
}

int main() {
std::cout << gcd_recursive(8, 12) << std::endl;
std::cout << gcd_recursive2(8, 12) << std::endl;
std::cout << gcd_iterative(8, 12) << std::endl;
return 0;
}

csharp

public static int gcd(int a, int b)
{
if (b == 0)
return a;
else
return gcd(b, a % b);
}

erlang

-module(gcd).
-export([gcd/2]).

gcd(A, 0) -> A;
gcd(A, B) -> gcd(B, A rem B).

fantom

gcd := |Int a, Int b -> Int| {
pair := [a, b].sort
while (pair.first != 0)
pair.set(1, pair.last % pair.first).swap(0, 1)
return pair.last
}
echo(gcd(12, 8)) // a>b, result == 4
echo(gcd(1029, 1071)) // a<b, result == 21

fsharp

let rec gcd x y =
if y = 0 then x
else gcd y (x % y)

groovy

static def gcd(int i, int j) {
if (Math.min(i,j)==0) return Math.max(i,j)
else return gcd(Math.min(i,j),Math.abs(i-j))
}

haskell

8 `gcd` 12

java

static int gcd(int a, int b) {
if (Math.min(a, b) == 0)
return Math.max(a, b);
else
return gcd(Math.min(a, b), Math.abs(a - b));
}

ocaml

(* tail recursive *)
let rec gcd n m =
if m = 0 then
n
else if n > m then
gcd (n-m) m
else
gcd n (m-n)
;;

perl

sub gcd {
my ($a, $b) = @_;
($a,$b) = ($b,$a) if $a > $b;

while ($a) { ($a, $b) = ($b % $a, $a) }

return $b;
}

print gcd( 8, 12 );

my $g = gcd (8, 12);
print $g;

sub gcd {
# Euclid's Algorithm - recursive
my ($c, $d) = @_;
return $c unless $d;
return gcd ($d, $c % $d);
}

my $g = gcd2 (8, 12);
print $g;

sub gcd2 {
# Dijkstra's Algorithm - recursive
my ($c, $d) = @_;
return $c if $c == $d;
return $c > $d? gcd2 ($c - $d, $d) : gcd2 ($c, $d - $c);
}

python

def gcd_recursive(i, j):
if min(i, j) == 0:
return max(i, j)
else:
return gcd_recursive(min(i, j), abs(i - j))

def gcd_iterative(i, j):
while min(i, j) != 0:
i, j = min(i, j), abs(i - j)
return max(i, j)

if __name__ == "__main__":
print gcd_recursive(8, 12)
print gcd_iterative(8, 12)

from fractions import gcd
print gcd(8, 12)

ruby

135.gcd(30)
# => 15

scala

def gcd(x: Int, y: Int): Int =
if (b == 0) x
else gcd(b, x % y)