langref.org - clojure, cpp, fsharp, groovy ...

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");

fsharp

printfn "Hello World!"

groovy

println "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";;

python

print "Hello World!"

scala

println("Hello World!")

printf("Hello World!\n")

Retrieve a string containing ampersands from the variables in a url

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

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

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

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

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

clojure

(->> {"mode" "view"
"fname" "Ron & Jean"
"lname" "Smith"}
(map #(str (URLEncoder/encode (first %) "UTF-8")
"="
(URLEncoder/encode (second %) "UTF-8")))
(reduce (fn [url e] (str url "&" e))
"http://myserver.com/custinfo/edit.php"))

cpp

QUrl url("http://myserver.com/custinfo/edit.php");
url.addQueryItem("mode", "view");
url.addQueryItem("fname", "Ron & Jean");
url.addQueryItem("lname", "Smith");
QByteArray encodedUrl = url.toEncoded();

fsharp

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

// Example that shows encoding and decoding:
let queryString =
let fname = HttpUtility.UrlEncode("Ron & James")
let lname = HttpUtility.UrlEncode("Smith & Jones")
sprintf "http://myserver.com/custinfo/edit.php?mode=view&fname=%s&lname=%s" fname lname
/// All parameters in the URL as a lookup map
let parameters =
let paramStart = queryString.IndexOf('?')
if paramStart < 0 then
Map.empty
else
let values =
queryString.Substring(paramStart + 1)
|> HttpUtility.ParseQueryString
values.AllKeys
|> Seq.map (fun key -> key, values.[key])
|> Map.ofSeq
let fname = parameters.TryFind("fname")
let lname = parameters.TryFind("lname")

groovy

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

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

java

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

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

ocaml

let query =
Netencoding.Url.mk_url_encoded_parameters [
"mode", "view";
"fname", "Ron & Jean";
"lname", "Smith";
]

let url =
"http://myserver.com/custinfo/edit.php?" ^ query

python

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

from urllib import urlencode

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

print urlencode(query_dict.items())

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

scala

import java.net.URLEncoder

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

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

println(url)

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

Declaration

Define a string containing special characters

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

clojure

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

cpp

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

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

fsharp

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

groovy

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

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

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

java

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

ocaml

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

python

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

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";

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"

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"

python

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

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

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;

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

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);;

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)

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());

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()

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
;;

python

"reverse me"[::-1]

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();

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)

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)
;;

python

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

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);
}

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 }

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

python

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

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();

fsharp

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

let trimmed = " hello ".Trim()

groovy

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

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

python

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

scala

val s = " hello ".trim

Simple substitution cipher

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

clojure

(use 'clojure.contrib.cond)

(defn rot13 [s]
(reduce str
(map #(char (let [c (bit-and (int (char %)) 0xDF)]
(+ % (cond-let [i]
(and (>= c (int \A)) (<= c (int \M))) 13
(and (>= c (int \N)) (<= c (int \Z))) -13
true 0))))
(map #(int (char %)) s))))

(defn rot47 [s]
(reduce str
(map #(char (+ % (cond-let [i]
(and (>= % (int \!)) (<= % (int \O))) 47
(and (>= % (int \P)) (<= % (int \~))) -47
true 0)))
(map #(int (char %)) s))))

cpp

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

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

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

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

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

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

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

fsharp

#light

let rotChar (s:int) (l:int) (h:int) (c:char) =
let charCode = int c
let letterCount = h - l + 1
let newCharCode = (charCode - l + s) % letterCount + l
char newCharCode

let rot13 (text:string) =
let rotChar13 = function
| (c:char) when 'A' <= c && c <= 'Z' -> rotChar 13 (int 'A') (int 'Z') c
| c when 'a' <= c && c <= 'z' -> rotChar 13 (int 'a') (int 'z') c
| c -> c
new string([| for c in text -> rotChar13 c|])

let rot47 (text:string) =
let rotChar47 = function
| ' ' as c -> c
| c -> rotChar 47 (int '!') (int '~') c
new string([| for c in text -> rotChar47 c |])

groovy

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

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

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

java

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

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

ocaml

let rot_char13 c = match c with
| 'A'..'M' | 'a'..'m' -> Char.chr ((Char.code c) + 13)
| 'N'..'Z' | 'n'..'z' -> Char.chr ((Char.code c) - 13)
| _ -> c

let rot_char47 c = match c with
| '!'..'N' -> Char.chr ((Char.code c) + 47)
| 'O'..'~' -> Char.chr ((Char.code c) - 47)
| _ -> c

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

let rot13 = rot rot_char13
let rot47 = rot rot_char47

python

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

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

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

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

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

scala

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

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

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

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

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

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

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);

fsharp

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

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

groovy

println "Space Monkey".toUpperCase()

java

String upper = text.toUpperCase();

ocaml

String.uppercase "Space Monkey";;

python

"Space Monkey".upper()

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();

fsharp

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

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

groovy

println "Caps ARE overRated".toLowerCase()

java

"Caps ARE overRated".toLowerCase();

ocaml

String.lowercase "Caps ARE overRated";;

python

"Caps ARE overRated".lower()

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();

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")

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")

python

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

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

"man OF stEEL".title()

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);

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))

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.);;

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)

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;

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)

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;;

python

"%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;

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)

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;;

python

"%-6s" % 1024

str(1024).rjust(6)

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

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;

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)

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;;

python

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

round(7./8., 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;

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

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;;

python

"%10s" % 73

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();

fsharp

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

groovy

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

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;;

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)

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);

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

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);;

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)

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;

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'

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";;

python

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

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;

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

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)

python

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

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");

fsharp

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

groovy

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

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

python

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

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();
}

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] }

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
)

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"))

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

Replacing

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

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

clojure

(.replaceFirst (re-matcher #"e" "Red Green Blue") "*")

cpp

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

fsharp

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

groovy

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

java

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

ocaml

let replaced = Str.replace_first (Str.regexp "e") "*" "Red Green Blue" in
print_endline replaced ;;

python

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

scala

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

Replace all regex matches in a string with a static string

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

clojure

(.replaceAll (re-matcher #"se\w+" "She sells sea shells") "X")

cpp

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

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

fsharp

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

groovy

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

java

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

ocaml

let s = "She sells sea shells" in
Str.global_replace (Str.regexp "se[^ \\t\\n]*") "X" s

python

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

scala

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

Replace all regex matches in a string with a dynamic string

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

clojure

(def *string* "The {Quick} Brown {Fox}")
(def *regex* (re-pattern #"\{(\w+)\}"))

(println
(loop [result ""
src *string*
replace-strs (re-seq *regex* *string*)]
(if (empty? src)
result
(let [[match replacement] (first replace-strs)]
(if (= (first src) (first match))
; At the beginning of a sequence that should be replaced.
; Do replacement of a single match
(recur (str result (apply str (reverse replacement)))
(drop (count match) src)
(rest replace-strs))
; else, just copy one char from the source to the result
(recur (str result (first src))
(rest src)
replace-strs))))))

(clojure.string/replace "The {Quick} Brown {Fox}"
#"\{(\w+)\}"
(fn [[_ word]] (apply str (reverse word))))

cpp

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

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

fsharp

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

groovy

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

java

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

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

ocaml

let s = "The {Quick} Brown {Fox}" in
let r = Str.regexp "{\$[^ \\t\\n]*\$}" in
Str.global_substitute r (fun m -> string_rev (Str.matched_group 1 m)) s

python

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

scala

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

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

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;

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

java

List list = Collections.emptyList();

String[] list = {};

ocaml

let list = [];;

python

list = []

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";

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+

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" ];;

python

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

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, ", ");

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]

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

python

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

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);
}
}

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() == ""

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 ""

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(*[]) == ""

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;

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()

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
)

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])]

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;

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"]

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"];;

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]

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];

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

java

String result = list.get(2);

ocaml

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

python

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

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();

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]

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"]

python

list = ['Red', 'Green', 'Blue']
list[-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);

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']

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;;

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)

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"));

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

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];;

python

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

unique_ages = list(set(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);

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)

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"]

python

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

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);

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)

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 []

python

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

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)

java

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

Collections.rotate(list, -1);

ocaml

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

python

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

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

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));

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]

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

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)

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;

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

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 :("

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

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(); });

fsharp

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

groovy

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

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"];;

python

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

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

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'
}

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]

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']

python

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

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

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

Declaration

Define an empty map

clojure

(def m {})

cpp

Hashtable^ hash = gcnew Hashtable;

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

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

fsharp

let map = Map.empty

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

let map = new Hashtable()

groovy

def map = [:]

Map map = new HashMap();

java

Map map = new HashMap();

ocaml

module StringMap = Map.Make (String)
let m = StringMap.empty

let m = Hashtbl.create 42

python

map = {}

scala

val map = mutable.Map.empty

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

val map = Map()

Define an unmodifiable empty map

clojure

; Clojure maps are immutable
(def m {})

cpp

const std::map<T1,T2> immutable_map_instance_of_type_t1_to_t2;

fsharp

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

groovy

empty = Collections.EMPTY_MAP

map = [:].asImmutable()

def empty = MapUtils.EMPTY_SORTED_MAP

def empty = ImmutableMap.of()

java

Map empty = Collections.EMPTY_MAP;

SortedMap empty = MapUtils.EMPTY_SORTED_MAP;

ocaml

(* OCaml maps are functional data structures (so are immutable) *)
module StringMap = Map.Make (String)
let m = StringMap.empty

python

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

scala

val map = immutable.Map.empty

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

val map = Map()

Define an initial map

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

clojure

(def m '{circle 1 triangle 1 square 4})

cpp

Hashtable^ shapes = gcnew Hashtable;

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

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

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

map<string, int> shapes;

shapes["circle"] = 1;
shapes["triangle"] = 3;
shapes["square"] = 4;

fsharp

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

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

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

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

groovy

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

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

java

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

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

ocaml

module StringMap = Map.Make (String)

let m0 = StringMap.empty

let m1 = StringMap.add "circle" 1 m0
let m2 = StringMap.add "triangle" 3 m1
let m3 = StringMap.add "square" 4 m2

let m = Hashtbl.create 42;;

Hashtbl.replace m "circle" 1;;
Hashtbl.replace m "triangle" 3;;
Hashtbl.replace m "square" 4;;

python

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

scala

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

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

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

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

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

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

val map = Map("circle" -> 1, "triangle" -> 3, "square" -> 4)

Access

Check if a key exists in a map

Given a map pets {joe:cat,mary:turtle,bill:canary} print "ok" if an pet exists for "mary"

clojure

(if (contains? '{joe cat mary turtle bill canary} 'mary)
(println "ok"))

cpp

if (pets->ContainsKey("mary")) Console::WriteLine("ok");

if (pets.find("mary") != pets.end()){
std::cout << "ok" << std::endl;
}

if (pets.count("mary") > 0)
cout << "ok" << endl;

fsharp

if (Map.mem "mary" pets) then printfn "ok"

if pets.ContainsKey("mary") then printfn "ok"

groovy

pets = [joe:'cat', mary:'turtle', bill:'canary']
if(pets.containsKey('mary')) println 'ok'

pets = [joe:'cat', mary:'turtle', bill:'canary']
if(pets.mary) println 'ok'

java

if (pets.containsKey("mary")) System.out.println("ok");

ocaml

module StringMap = Map.Make (String)

let map =
List.fold_left (fun map (key, value) ->
StringMap.add key value map
) StringMap.empty [("joe", "cat"); ("mary", "turtle"); ("bill", "canary")]

let () =
if StringMap.mem "mary" map
then print_endline "OK"

let () =
let map = Hashtbl.create 42 in
List.iter (fun (key, value) ->
Hashtbl.add map key value
) [("joe", "cat"); ("mary", "turtle"); ("bill", "canary")];

if Hashtbl.mem map "mary" then print_endline "OK"

python

pets = dict(joe='cat', mary='turtle', bill='canary')
if ("mary" in pets) print "ok"

scala

if (pets.contains("mary")) println("ok")

map.get("mary").foreach(println("ok"))

Retrieve a value from a map

Given a map pets {joe:cat,mary:turtle,bill:canary} print the pet for "joe" ("cat")

clojure

(def pets '{joe cat mary turtle bill canary})

(println (get pets 'joe))

cpp

if (pets->ContainsKey("joe")) Console::WriteLine(pets["joe"]);

cout << pets["joe"] << endl;

fsharp

if (Map.mem "joe" pets) then printfn "%s" (Map.find "joe" pets)

if (pets |> Map.exists (fun key _ -> key = "joe")) then printfn "%s" (Map.find "joe" pets)

let key = "joe"
match (pets |> Map.tryfind key) with
| Some(value) -> printfn "%s" value
| None -> printfn "Key %s not found" key

if pets.ContainsKey("joe") then printfn "%s" pets.["joe"]

if pets.ContainsKey("joe") then printfn "%s" (pets.["joe"] :?> string)

groovy

pets = [joe:'cat', mary:'turtle', bill:'canary']
assert pets['joe'] == 'cat'

assert pets.joe == 'cat'

java

String pet = pets.get("joe");

ocaml

module StringMap = Map.Make (String)

let map =
List.fold_left (fun map (key, value) ->
StringMap.add key value map
) StringMap.empty [("joe", "cat"); ("mary", "turtle"); ("bill", "canary")]

let () =
try
let pet = StringMap.find "joe" map in
Printf.printf "Joe's pet is a %s.\n" pet
with Not_found ->
prerr_endline "No pet found for Joe."

let () =
let map = Hashtbl.create 42 in
List.iter (fun (key, value) ->
Hashtbl.add map key value
) [("joe", "cat"); ("mary", "turtle"); ("bill", "canary")];

try
let pet = Hashtbl.find map "joe" in
Printf.printf "Joe's pet is a %s.\n" pet
with Not_found ->
prerr_endline "No pet found for Joe."

python

print pets['joe']

scala

if (pets.contains("joe")) println(pets("joe"))

println(pets.getOrElse("joe", "*** no pet owned ***"))

pets("joe")

Add an entry to a map

Given an empty pets map, add the mapping from "rob" to "dog"

clojure

(assoc {} 'rob 'dog)

cpp

pets->Add("rob", "dog");

pets["rob"] = "dog";

fsharp

pets <- (Map.add "rob" "dog" pets)

pets.Add("rob", "dog")

groovy

pets['rob'] = 'dog'

pets.rob = 'dog'

pets.put('rob', 'dog')

java

pets.put("rob", "dog");

ocaml

module StringMap = Map.Make (String)

let pets = StringMap.add "rob" "dog" StringMap.empty

let () =
let map = Hashtbl.create 42 in
Hashtbl.replace map "rob" "dog"

python

pets['rob'] = 'dog'

scala

pets += "rob" -> "dog"

Remove an entry from a map

Given a map pets {joe:cat,mary:turtle,bill:canary} remove the mapping for "bill" and print "canary"

clojure

; Maps are immutable
; The following expression will return a new map without the 'bill key
(let [pets '{joe cat mary turtle bill canary}]
(println (get pets 'bill))
(dissoc pets 'bill))

cpp

if (pets->ContainsKey("bill"))
{
String^ value = safe_cast<String^>(pets["bill"]); pets->Remove("bill");
Console::WriteLine("{0}", value);
}

fsharp

let key = "bill"
match (pets |> Map.tryFind key) with
| Some(value) -> pets <- (Map.remove key pets) ; printfn "%s : %s removed" key value
| None -> printfn "Key %s not found" key

let key = "bill"
let entry = if (pets.ContainsKey(key)) then Some(pets.[key]) ; else None
pets.Remove(key)

match entry with
| Some(value) -> printfn "%s" value
| None -> printfn "key not found"

groovy

pets = [joe:'cat', mary:'turtle', bill:'canary']
println pets.remove('bill')

java

System.out.println(pets.remove("bill"))

ocaml

module StringMap = Map.Make (String)

let pets =
List.fold_left (fun map (key, value) ->
StringMap.add key value map
) StringMap.empty [("joe", "cat"); ("mary", "turtle"); ("bill", "canary")]

let get_and_rem key m =
try
let value = StringMap.find key m in
let rm = StringMap.remove key m in
Some (value, rm)
with Not_found ->
None

let () =
let key = "bill" in
match get_and_rem key pets with
| Some (found, new_pets) ->
Printf.printf "%s : %s removed\n" key found
| None ->
Printf.printf "Key %s not found" key

let get_and_rem m key =
try
let value = Hashtbl.find m key in
Hashtbl.remove m key;
Some value
with Not_found ->
None

let () =
let pets = Hashtbl.create 42 in
List.iter (fun (key, value) ->
Hashtbl.add pets key value
) [("joe", "cat"); ("mary", "turtle"); ("bill", "canary")];

let key = "bill" in
match get_and_rem pets key with
| Some found ->
Printf.printf "%s : %s removed\n" key found
| None ->
Printf.printf "Key %s not found" key

python

print pets.pop('bill')

scala

val pet = pets("bill") ; pets -= "bill" ; println(pet)

println(pets.removeKey("bill") match { case Some(pet) => pet ; case None => "***" })

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;

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 }

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

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)

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);
}

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() }

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"]

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)

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;

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!"

java

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

ocaml

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

python

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

scala

val name = "Bob"
if (name.equals("Bob")) printf("Hello, %s!\n", name)

val name = "Bob"

// Scala supports operator overloading, so the following works correctly
if (name == "Bob") printf("Hello, %s!\n", name)

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"));

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")

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"

python

if age > 42:
print 'You are old'
else:
print 'You are young'

print age > 42 and 'You are old' or 'You are 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" ) )

Perform different actions depending on several boolean conditions (IF .. THEN .. ELSIF .. ELSE)

clojure

(println
(condp <= age
84 "You are really ancient"
30 "You are middle aged"
"You are young"))

cpp

if (age > 84) Console::WriteLine("You are really ancient");
else if (age > 30) Console::WriteLine("You are middle-aged");
else Console::WriteLine("You are young");

Console::WriteLine("You are {0}", (age > 84 ? "really ancient" : age > 30 ? "middle-aged" : "young"));

std::cout << "You are " << (age > 84 ? "really ancient" : age > 30 ? "middle-aged" : "young") << std::endl;

fsharp

if age > 84 then printfn "You are really ancient"
elif age > 30 then printfn "You are middle-aged"
else printfn "You are young"

let message = match age with
| _ when age > 84 -> "really ancient"
| _ when age > 30 -> "middle-aged"
| _ -> "young"
printfn "You are %s" message

groovy

if (age > 84)
println "You are really ancient"
else if (age > 30)
println "You are middle-aged"
else
println "You are young"

java

if (age > 84) System.out.println("You are really ancient");
else if (age > 30) System.out.println("You are middle-aged");
else System.out.println("You are young");

ocaml

if age > 84 then
print_endline "You are really ancient"
else if age > 30 then
print_endline "You are middle-aged"
else
print_endline "You are young"

python

if age > 84:
print 'You are really ancient'
elif age > 30:
print 'You are middle-aged'
else:
print 'You are young'

scala

val age = 65

if (age > 84) println("You are really ancient")
else if (age > 30) println("You are middle-aged")
else println("You are young")

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();
}

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)}"
}

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 ()

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)]

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;

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()

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()

python

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

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();

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 ','
}

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 ()

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()))

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");

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()

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

python

print "Hello" * 5

for i in range(5):
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!");

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!"

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!"

python

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

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

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"

python

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

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"
}

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

python

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

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!");
}

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'

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)

python

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

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!");
}

fsharp

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

groovy

file << 'some text'

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

python

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

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);

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) }

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

python

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

scala

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

Process each file in a directory recursively

clojure

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

cpp

void processFile(String^ filename) { Console::WriteLine("{0}", filename); }

void processDirectory(String^ dirname)
{
for each(String^ filename in IO::Directory::GetFiles(dirname)) processFile(filename);
for each(String^ subdirname in IO::Directory::GetDirectories(dirname)) processDirectory(subdirname);
}

int main()
{
processDirectory("c:\\");
}

fsharp

let processDirectory dirname proc =
let rec processDirectory' dirname' =
Directory.GetFiles(dirname') |> Array.iter proc
Directory.GetDirectories(dirname') |> Array.iter processDirectory'
processDirectory' dirname

// ------

let dirname = "c:\\"

processDirectory dirname (fun filename -> printfn "%s" filename)

groovy

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

java

processDirectory(new File("c:\\"));

ocaml

let rec recurse_dir dir f =
let filenames = Sys.readdir dir in
Array.iter (fun name ->
let fullname = Filename.concat dir name in
if Sys.is_directory fullname then
recurse_dir fullname f
else
f fullname
) filenames
;;
recurse_dir (Sys.getenv "HOME") print_endline ;;

python

import os
results = (process(os.path.join(p, n)) for p,d,l in os.walk(".") for n in l)

scala

processDirectory(new File("c:\\"))

Dates

Parsing

Parse a date and time from a string

Given the string "2008-05-06 13:29", parse it as a date representing 6th March, 2008 1:29:00pm in the local time zone.

clojure

(.. (SimpleDateFormat. "yyyy-MM-dd HH:mm")
(parse "2008-05-06 13:29"))

cpp

DateTimeOffset^ dateTime = DateTimeOffset::Parse("2008-05-06 13:29");

// Use format specifiers to appropriately format string
// 1. Default culture
Console::WriteLine("{0}", dateTime->ToString("d MMMM, yyyy h:mm:sstt"));

// 2. Nominated culture
Console::WriteLine("{0}", dateTime->ToString("d MMMM, yyyy h:mm:sstt"), Globalization::CultureInfo::CreateSpecificCulture("en-us"));

DateTimeOffset^ dateTime = DateTimeOffset::Parse("2008-05-06 13:29");

// Customize date/time string
Text::StringBuilder^ dsb = gcnew Text::StringBuilder(40);
dsb->Append(dateTime->ToString("%d"))->Append("th ")->Append(dateTime->ToString("MMMM, yyyy h:mm:ss"))->Append(dateTime->ToString("tt")->ToLower());

Console::WriteLine("{0}", dsb);

fsharp

let dateTime = DateTimeOffset.Parse("2008-05-06 13:29")

// Use format specifiers to appropriately format string
// 1. Default culture
printfn "%s" (dateTime.ToString("d MMMM, yyyy h:mm:sstt"))

// 2. Nominated culture
Console.WriteLine("{0}", dateTime.ToString("d MMMM, yyyy h:mm:sstt"), Globalization.CultureInfo.CreateSpecificCulture("en-us"))

let dateTime = DateTimeOffset.Parse("2008-05-06 13:29")

// Customize date/time string
let dsb = ((new StringBuilder(40)).Append(dateTime.ToString("%d")).Append("th ").Append(dateTime.ToString("MMMM, yyyy h:mm:ss")).Append(dateTime.ToString("tt").ToLower()))

printfn "%s" (dsb.ToString())

groovy

def date = new SimpleDateFormat("yyy-MM-dd HH:mm").parse("2008-05-06 13:29")

def date = Date.parse("yyy-MM-dd HH:mm", "2008-05-06 13:29")

java

DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm");
Date date = df.parse("2008-05-06 13:29");

DateTimeFormatter fmt = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm");
DateTime dt = fmt.parseDateTime("2008-05-06 13:29");

ocaml

let s = "2008-05-06 13:29" in
let r = Str.regexp "\$[0-9][0-9][0-9][0-9]\$-\$[0-9][0-9]\$-\$[0-9][0-9]\$ \$[0-9][0-9]\$:\$[0-9][0-9]\$" in
assert (Str.string_match r s 0);
Unix.mktime { Unix.tm_sec = 0;
tm_min = int_of_string (Str.matched_group 5 s);
tm_hour = int_of_string (Str.matched_group 4 s);
tm_mday = int_of_string (Str.matched_group 3 s);
tm_mon = int_of_string (Str.matched_group 2 s) - 1;
tm_year = int_of_string (Str.matched_group 1 s) - 1900;
tm_wday = -1;
tm_yday = -1;
tm_isdst = true; (** Daylight time savings in effect *)
}

python

import time
time.strptime("2008-05-06 13:29", "%Y-%m-%d %H:%M")

scala

val date = new SimpleDateFormat("yyy-MM-dd HH:mm").parse("2008-05-06 13:29")

Printing

Display information about a date

Display the day of month, day of year, month name and day name of the day 8 days from now.

clojure

(let [cal (Calendar/getInstance)]
(.add cal Calendar/DAY_OF_YEAR 8)
(println (.format (SimpleDateFormat. "d, D, MMMM, EEEE")
(.getTime cal))))

cpp

QDate dateEightDaysFromNow = QDate::currentDate().addDays(8);

fsharp

Using F# interactive

> let Then = DateTime.Now.AddDays(8.0)
- let dayNumber = Then.DayOfYear.ToString()
- let solution = Then.ToString("dd " + dayNumber + " MMMM dddd");;

val Then : DateTime = 08/08/2010 08:58:05
val dayNumber : string = "220"
val solution : string = "08 220 August Sunday"

>

groovy

use (TimeCategory) {
eight_days_time = 1.week.from.now + 1.day
}
println eight_days_time[DAY_OF_MONTH]
println eight_days_time.format('d') // alternative to above
println eight_days_time[DAY_OF_YEAR]
println eight_days_time.format('MMMM')
println eight_days_time.format('EEEE')

java

Calendar cal = Calendar.getInstance();
cal.add(DAY_OF_YEAR, 8);
System.out.println(cal.get(DAY_OF_MONTH));
System.out.println(cal.get(DAY_OF_YEAR));
System.out.println(new SimpleDateFormat("MMMM").format(cal.getTime()));
System.out.println(new SimpleDateFormat("EEEE").format(cal.getTime()));

ocaml

let days = [| "Sunday"; "Monday"; "Tuesday"; "Wednesday"; "Thursday"; "Friday"; "Saturday" |]
let months = [| "January"; "February"; "March"; "April"; "May"; "June"; "July"; "August"; "September"; "October"; "November"; "December" |]

let current_time = Unix.time () in
let one_day = 86400. (* seconds *) in
let future_time = Unix.localtime (current_time +. 8. *. one_day) in
Printf.printf "day of month = %d, day of year = %d, month name = %s, day name = %s\n"
future_time.Unix.tm_mday
future_time.Unix.tm_yday
months.(future_time.Unix.tm_mon)
days.(future_time.Unix.tm_wday)

python

from datetime import datetime, timedelta

eightDaysFromNow = datetime.now() + timedelta(days=8)

print eightDaysFromNow.strftime('%d') # day of month
print eightDaysFromNow.strftime('%j') # day of year
print eightDaysFromNow.strftime('%B') # month name FULL
print eightDaysFromNow.strftime('%A') # day of week name FULL

scala

import java.util.Calendar
import java.text.SimpleDateFormat

val formatString = "d, D, MMMM, EEEE"
val cal = Calendar.getInstance

cal.add(Calendar.DAY_OF_YEAR, 8)

println(new SimpleDateFormat(formatString) format cal.getTime)

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);

fsharp

printfn "%A" System.DateTime.Now

groovy

println new Date()

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 ())

python

from datetime import datetime
print datetime.utcnow()

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);
}

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()

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

python

class Greeter(object):
""" Greet someone.
"""
def __init__(self, whom):
self._whom = whom
def greet(self):
print "Hello, %s!" % self._whom

Greeter("world").greet()

scala

class Greeter(whom : String) { def greet() = { printf("Hello %s\n", whom) } }

(new Greeter("world!")).greet()

Instantiate object with mutable state

Reimplement the Greeter class so that the 'whom' property or data member remains private but is mutable, and is provided with getter and setter methods. Invoke the setter to change the greetee, invoke 'greet', then use the getter in displaying the line, "I have just greeted {whom}.".

For example, if the greetee is changed to 'Tommy' using the setter, the 'greet' method would display:

Hello, Tommy!

The getter would then be used to display the line:

I have just greeted Tommy.

clojure

(defn greeter [whom]
(atom {:whom whom}))

(defn get-whom [g]
(:whom @g))

(defn set-whom [g whom]
(swap! g #(conj % {:whom whom})))

(defn greet [g]
(println (str "Hello, " (:whom @g) "!")))

; using the "class"
(let [g (greeter "world")]
(greet g)
(set-whom g "Tommy")
(greet g)
(println (str "I have just greeted " (get-whom g) ".")))

; or same effect without using any variables
(println (str "I have just greeted "
(get-whom (doto (greeter "world")
(greet)
(set-whom "Tommy")
(greet)))
"."))

cpp

#include <iostream>

using namespace std;

class Greeter {
string whom_;

public:
Greeter(const string &whom) : whom_(whom) {}

string get_whom() const {
return whom_;
}

void set_whom(const string &whom) {
whom_ = whom;
}

void greet() const {
cout << "Hello " << whom_ << "!" << endl;
}
};

int main()
{
Greeter greeter("world");
greeter.greet();
greeter.set_whom("Tommy");
greeter.greet();
cout << "I have just greeted " + greeter.get_whom() << "." << endl;
}

fsharp

type Greeter(name:string) =
let mutable whom = name

member this.Whom
with get () = whom
and set v = whom <- v

member this.Greet() =
printfn "Hello, %s!" whom

let greeter = Greeter("World")
greeter.Greet()
greeter.Whom <- "Tommy"
greeter.Greet()
printfn "I have just greeted %s." greeter.Whom

groovy

class Greeter {
def whom
def greet() { println "Hello, $whom!" }
}

greeter = new Greeter(whom:"world"); greeter.greet()

greeter.whom = 'Tommy'; greeter.greet()
println "I have just greeted $greeter.whom"

java

class Greeter {
private String whom;

public Greeter(String whom) {
this.whom = whom;
}

public String getWhom() {
return whom;
}

public void setWhom(String whom) {
this.whom = whom;
}

public void greet() {
System.out.println("Hello " + whom + "!");
}
}
Greeter greeter = new Greeter("World");
greeter.greet();
greeter.setWhom("Tommy");
greeter.greet();
System.out.println("I have just greeted " + greeter.getWhom() + ".");

ocaml

class greeter =
object
val mutable whom = "someone"
method set_whom greetee = whom <- greetee
method get_whom = whom
method greet = Printf.printf "Hello, %s!\n" whom
end;;

let o = new greeter in
o#set_whom "Tommy";
o#greet;
Printf.printf "I have just greeted %s.\n" o#get_whom

python

class Greeter(object):
_whom = None

def __init__(self, whom):
self._whom = whom

@property
def whom(self):
return self._whom

@propset(whom)
def whom(self, value=None):
self._whom = value

def greet(self):
print 'Helo, %s!' % self._whom

greeter = Greeter('Winston')
greeter.greet()
greeter.whom = 'Tommy'
greeter.greet()

# required for Python 2.5 or less
def propset(prop):
assert isinstance(prop, property)
def helper(func):
return property(prop.fget, func, prop.fdel, prop.__doc__)
return helper

class Greeter(object):
_whom = None

def __init__(self, whom):
self._whom = whom

@property
def whom(self):
return self._whom

@propset(whom)
def whom(self, value=None):
self._whom = value

def greet(self):
print 'Helo, %s!' % self._whom

greeter = Greeter('Winston')
greeter.greet()
greeter.whom = 'Tommy'
greeter.greet()

scala

class Greeter(var whom: String) {
def greet() = println("Hello " + whom + "!")
}

// Is this really a private value with getter and setter methods,
// or just a public mutable value?

val greeter = new Greeter("World")
greeter.greet()
greeter.whom = "Tommy"
greeter.greet()
printf("I have just greeted %s.\n", greeter.whom)

Inheritance

Implement Inheritance Heirarchy

Implement a Shape abstract class which will form the base of an inheritance hierarchy that models 2D geometric shapes. It will have:

* A non-mutable 'name' property or data member set by derived or descendant classes at construction time
* A 'area' method intended to be overridden by derived or descendant classes ( double precision floating point return value)
* A 'print' method (also for overriding) will display the shape

's name, area, and all shape-specific values



Two derived or descendant classes will be created:

* Circle    -> Constructor requires a '

radius' argument, and a 'circumference

' method to be implemented  

* Rectangle -> Constructor requires '

length' and 'breadth' arguments, and a 'perimeter

' method to be implemented 



Instantiate an object of each class, and invoke each objects '

print' method to show relevant details.

clojure

(defmulti area :Shape)
(defmulti print :Shape)

; Circle methods
(defn circle [r]
{:Shape :Circle
:name "Circle"
:radius r})

(defn circumference [c]
(* 2 Math/PI (:radius c)))

(defmethod area :Circle [c]
(* Math/PI (:radius c) (:radius c)))

(defmethod print :Circle [c]
(println (format "I am a %s with ->" (:name c)))
(println (format "Radius: %.2f" (:radius c)))
(println (format "Area: %.2f" (area c)))
(println (format "Circumference: %.2f" (circumference c))))

; Rectangle methods
(defn rectangle [l b]
{:Shape :Rectangle
:name "Rectangle"
:length l
:breadth b})

(defn perimeter [r]
(+ (* 2 (:length r)) (* 2 (:breadth r))))

(defmethod area :Rectangle [r]
(* (:length r) (:breadth r)))

(defmethod print :Rectangle [r]
(println (format "I am a %s with ->" (:name r)))
(println (format "Length, Width: %.2f, %.2f" (:length r) (:breadth r)))
(println (format "Area: %.2f" (area r)))
(println (format "Perimeter: %.2f" (perimeter r))))

; usage of the "classes"
(let [shapes (list (circle 4.2) (rectangle 2.7 3.1) (rectangle 6.2 2.6) (circle 17.3))]
(doseq [shape shapes]
(print shape)))

cpp

#include <string>
#include <iostream>

using namespace std;

static const double PI = 3.141592;

class Shape {
protected:
string name_;
public:
Shape(const string& name) : name_(name) { }
virtual double area() const = 0;
virtual void print() const = 0;
};

class Circle : public Shape {
double radius_;
public:
Circle(double radius) : Shape("circle"), radius_(radius) { }
double area() const {
return PI * radius_ * radius_;
}
void print() const {
cout << "A " << name_ << " with radius " << radius_ << ", area "
<< area() << " and circumference " << circumference() << "."
<< endl;
}
double circumference() const {
return 2 * PI * radius_;
}
};

class Rectangle : public Shape {
double length_;
double breadth_;
public:
Rectangle(double length, double breadth) :
Shape("rectangle"), length_(length), breadth_(breadth) { }
double area() const {
return length_ * breadth_;
}
void print() const {
cout << "A " << name_ << " with length " << length_ << ", breadth "
<< breadth_ << ", area " << area() << " and perimeter "
<< perimeter() << "." << endl;
}
double perimeter() const {
return 2 * length_ + 2 * breadth_;
}
};

int main(int argc, char *argv[])
{
Circle circle(4);
circle.print();
Rectangle rectangle(2, 5.5);
rectangle.print();
}

fsharp

[<AbstractClass>]
type Shape(name:string) =
member this.Name = name
abstract Area : float
abstract Print : unit -> unit

type Circle(name, radius:float) =
inherit Shape(name)
member this.Radius = radius
member this.Circumference =
System.Math.PI * radius * 2.
override this.Area =
System.Math.PI * radius * radius
override this.Print() =
printfn "Circle: %s" this.Name
printfn "Area: %f" this.Area
printfn "Circumference: %f" this.Circumference
printfn "Radius: %f" this.Radius

type Rectangle(name, length:float, breadth:float) =
inherit Shape(name)
member this.Length = length
member this.Breadth = breadth
member this.Perimiter =
(length * 2.) + (breadth * 2.)
override this.Area =
length * breadth
override this.Print() =
printfn "Rectangle: %s" this.Name
printfn "Area: %f" this.Area
printfn "Perimiter: %f" this.Perimiter
printfn "Length: %f" this.Length
printfn "Breadth: %f" this.Breadth

let c = Circle("Foo", 2.1)
let r = Rectangle("Bar", 2.2, 3.3)

c.Print()
printfn ""
r.Print()

groovy

abstract class Shape {
final name
Shape(name) { this.name = name }
abstract area()
abstract print()
}

class Circle extends Shape {
final radius
Circle(radius) {
super('circle')
this.radius = radius
}
def area() { Math.PI * radius * radius }
def circumference() { 2 * Math.PI * radius }
def print() {
println "I am a $name with ->"
printf 'Radius: %.2f\n', radius
printf 'Area: %.2f\n', area()
printf 'Circumference: %.2f\n', circumference()
}
}

class Rectangle extends Shape {
final length, breadth
def Rectangle(length, breadth) {
super("rectangle")
this.length = length
this.breadth = breadth
}
def area() { length * breadth }
def perimeter() { 2 * length + 2 * breadth }
def print() {
println "I am a $name with ->"
printf 'Length, Width: %.2f, %.2f\n', length, breadth
printf 'Area: %.2f\n', area()
printf 'Perimeter: %.2f\n', perimeter()
}
}

shapes = [new Circle(4.2), new Rectangle(2.7, 3.1), new Rectangle(6.2, 2.6), new Circle(17.3)]
shapes.each { shape -> shape.print() }

java

/*
* Will work with version 1.4 if you remove the @Override annotation
* and declare floating point numbers using the primitive "double"
*/
abstract class Shape {
protected final String name;
public Shape(String name) {
this.name = name;
}
public abstract Double area();
public abstract void print();
}
class Circle extends Shape {
private Double radius;
public Circle(Double radius) {
super("circle");
this.radius = radius;
}
@Override
public Double area() {
return Math.PI * Math.pow(radius, 2);
}
@Override
public void print() {
System.out.println("A " + name + " with radius " + radius
+ ", area " + area() + " and circumference "
+ circumference() + ".");
}
public Double circumference() {
return 2 * Math.PI * radius;
}
}
class Rectangle extends Shape {
private Double length, breadth;
public Rectangle(Double length, Double breadth) {
super("Rectangle");
this.length = length;
this.breadth = breadth;
}
@Override
public Double area() {
return length * breadth;
}
public Double perimeter() {
return 2 * length + 2 * breadth;
}
@Override
public void print() {
System.out.println("A " + name + " with length " + length
+ ", breadth " + breadth + ", area " + area()
+ " and perimeter " + perimeter() + ".");
}
}
Circle circle = new Circle(4d);
circle.print();
Rectangle rectangle = new Rectangle(2d, 5.5);
rectangle.print();

ocaml

class virtual shape =
object(self)
method name = "shape"
method virtual area : float
method print = Printf.sprintf "%s, area %f" self#name self#area
end ;;

let pi = 4. *. atan 1.

class circle radius =
object(self)
inherit shape as super
method name = "circle"
method area = radius *. radius *. pi
method circumference = radius *. 2. *. pi
method print = Printf.sprintf "%s, circumference %f" super#print self#circumference
end

class rectangle length breadth =
object(self)
inherit shape as super
method name = "rectangle"
method area = length *. breadth
method perimeter = 2. *. ( length +. breadth)
method print = Printf.sprintf "%s, perimeter %f" super#print self#perimeter
end

let c = new circle 5. in
let r = new rectangle 7. 3. in
print_endline c#print;
print_endline r#print

python

#Start with the import statements.
import math # necessary to get the value of pi

class Shape(object):
"""Shape Class"""
def __init__(self):
"""Constructor method"""
pass #Do nothing here
def area(self):
"""The area method"""
pass #Do nothing here
def print_(self):
"""
The print method. Note the trailing underscore - this is because
there is a reserved statement called 'print' in python 2.x. The
trailing underscore is the accepted method of re-using names without
rebinding them
"""
print 'The name is: %s' % self.name #Print the only property we currently have

def _getName(self):
"""The getter method for the 'name' property.
Note that getter methods are generally discouraged in python"""
return self._name

_name = None # The leading underscore gives a weak non-public value
# to a variable. Two leading underscores will mangle its
# name at runtime, to make it more difficult to access.
# Note there is no real 'private' variable type in python.
name = property(_getName, doc='The name of this object')
# property statements work like: property(fget=None, fset=None, fdel=None, doc=None)

class Circle(Shape):
"""Circle Class - a sub class of shape"""
def __init__(self, radius, name='Circle'):
"""Constructor method again"""
Shape.__init__(self) # init the super class
self.radius = radius # Store the radius
self._setCircumference()# Function call
self._name = name

def _setCircumference(self):
self.circumference = 2*math.pi*self.radius

def area(self):
'''Return the area of this circle'''
tmpAera = math.pi * self.radius**2
return tmpAera
def print_(self):
'''The print method'''
super(Circle, self).print_() # This calls the print_ method in
# the super classes of Circle, in
# this case Shape
print 'The radius is: %f' % self.radius
print 'The circumference is %f' % self.circumference
print 'The area is: %f' % self.area()

class Rectangle(Shape):
"""The Rectangle Class"""
def __init__(self, length, breadth, name='Rectangle'):
Shape.__init__(self)
self._name = name
self.length = length
self.breadth = breadth
self.perimeter()
def area(self):
return self.breadth*self.length
def perimeter(self):
self._perimeter = self.breadth*2+self.length*2
return self._perimeter # You have a method return a value and still
# safely call it without handling the return
# value. This would be collected by garbage
# collection.
def print_(self):
super(Rectangle, self).print_()
print 'The length is %f and the breadth is %f' %(self.length, self.breadth)
print 'The perimeter is: %f' %self._perimeter
print 'The area is: %f' % self.area()

if __name__ == '__main__':
rectangle = Rectangle(5,3)
circle = Circle(5, name='Round and Round')
rectangle.print_()
circle.print_()

scala

abstract class Shape (val name: String) {
def area : Double
def print()
}

class Circle (val radius: Double) extends Shape("Circle") {
def area = Math.Pi * radius * radius
def circumference = 2 * Math.Pi * radius
def print() {
println("I'm a " + name + " with")
printf(" * radius = %.2f\n", radius)
printf(" * area = %.2f\n", area)
printf(" * circumference = %.2f\n\n", circumference)
}
}

class Rectangle (val length: Double, val breadth: Double) extends Shape("Rectangle") {
def area = length * breadth
def perimeter = 2 * (length + breadth)
def print() {
println("I'm a " + name + " with")
printf(" * length = %.2f\n", length)
printf(" * breadth = %.2f\n", breadth)
printf(" * area = %.2f\n", area)
printf(" * perimeter = %.2f\n\n", perimeter)
}
}

val shapes = List(new Circle(5.4), new Rectangle(7.8, 6.5))
shapes foreach (_.print)

Implement and use an Interface

Create a Serializable interface consisting of 'save' and 'restore' methods, each of which:

* Accept a stream or handle or descriptor argument for the source or destination
* Save to destination or restore from source the properties or data members of the implementing class (restrict yourself to the primitive types 'int' and 'string')

Next, create a Person class which has 'name' and 'age' properties or data members and implements this interface. Instantiate a Person object, save it to a serial stream, and instantiate a new Person object by restoring it from the serial stream.

clojure

(defn person [name age]
{:name name :age age})

(defn show [p]
(println (format "Name=%s Age=%d" (:name p) (:age p))))

(defn save [p filename]
(with-out-writer filename (pr p)))

(defn restore [filename]
(read (PushbackReader. (reader filename))))

(let [p (person "Ken" 38)]
(show p)
(save p *person-fn*))

(let [ser-p (restore *person-fn*)]
(show ser-p))

cpp

struct person
{
person(){}
person(const string &name, int age) : name_(name), age_(age) {}

string name_;
int age_;

template<typename Archive>
void serialize(Archive &ar, const unsigned int version) {
ar & name_ & age_;
}
};

int main()
{
const char *fn = "filename.txt";

person k("Ken", 38);
{
ofstream ofs(fn);
archive::text_oarchive oa(ofs);
oa << k;
}

person restored_person;
{
ifstream ifs(fn);
archive::text_iarchive ia(ifs);
ia >> restored_person;
}

cout << "Name : " << restored_person.name_ << endl
<< "Age : " << restored_person.age_ << endl;
}

fsharp

// Since everyone else is using built-in functionality instead of
// defining an interface as required, I won't buck the trend.
// Maybe this problem should be named "Use serialization features" instead
// of "Implement and use an Interface"

open System
open System.IO
open System.Runtime.Serialization.Formatters.Binary

[<Serializable>]
type Person(name:string, age:int) =
member this.Name = name
member this.Age = age

let serialize x =
use ms = new MemoryStream()
let bf = new BinaryFormatter()
bf.Serialize(ms, x)
ms.ToArray()

let deserialize<'a> bytes =
use ms = new MemoryStream(bytes:byte[])
let bf = new BinaryFormatter()
bf.Deserialize(ms) :?> 'a

let before = Person("Joel", 35)
let bytes = serialize before
let after = deserialize<Person> bytes

printfn "Before: %s, %i" before.Name before.Age
printfn "After: %s, %i" after.Name after.Age

groovy

// Built-in functionality but with slightly different names. Showing usage:
class Person implements Serializable { String name; int age }
p1 = new Person(name:'John', age:21)
p2 = null
output = new ByteArrayOutputStream() // or FileOutputStream, etc.
output.withObjectOutputStream { oos -> oos << p1 }
input = new ByteArrayInputStream(output.toByteArray())
input.withObjectInputStream(getClass().classLoader){ ois -> p2 = ois.readObject() }
assert p2.name == 'John'
assert p2.age == 21

java

// Serialization to a file
class Person implements Serializable {
private static final long serialVersionUID = 1L;
private String name;
private int age;
public void setAge(int age) {
this.age = age;
}
public int getAge() {
return age;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public boolean equals(Object obj) {
if(obj == this) return true;
if(obj instanceof Person) {
Person p = (Person) obj;
return (p.getName().equals(this.getName())
& p.getAge() == this.getAge());
}
return false;
}
public String toString() {
return "Name: " + name + ", age: " + age;
}
}
Person person = new Person();
person.setName("Gaylord Focker");
person.setAge(21);

try {
File file = new File("ser.obj");
FileOutputStream fos = new FileOutputStream(file);
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(person);
oos.close();
FileInputStream fis = new FileInputStream(file);
ObjectInputStream ois = new ObjectInputStream(fis);
Person deserializedPerson = (Person) ois.readObject();
ois.close();
System.out.println(deserializedPerson);
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}

ocaml

(* in OCaml, interfaces are class types, and have nothing to do with inheritance,
so I'm not sure what's the correct answer to this problem (if any) *)

class type serializable =
object
method save: out_channel -> unit
method restore: in_channel -> unit
end

class person name age =
object
val mutable my_name = name
val mutable my_age = age
method save oc = output_value oc my_name; output_value oc my_age
method restore ic = my_name <- input_value ic; my_age <- input_value ic
method print = Printf.printf "I'm %s, %d\n" my_name my_age
end

let transfer (o1: serializable) (o2: serializable) =
let temp_filename = "_person" in
let backing_store_save = open_out_bin temp_filename in
o1#save backing_store_save;
close_out backing_store_save;

let backing_store_restore = open_in_bin temp_filename in
o2#restore backing_store_restore;
close_in backing_store_restore

let o = new person "john" 42 in
let o2 = new person "nobody" 0 in
transfer (o :> serializable) (o2 :> serializable);
o2#print

python

import pickle

class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def __str__(self):
return "Name: {name}, age: {age}".format(name=self.name, age=self.age)

person = Person("Gaylord Focker", 21)
with open("person.pickle", "wb") as outstream:
pickle.dump(person, outstream)
with open("person.pickle", "rb") as instream:
deserialized_person = pickle.load(instream)
print(deserialized_person)

scala

class Person (var name: String, var age: Int) extends Serializable

val p1 = new Person("John", 21)
val output = new ByteArrayOutputStream()
val oos = new ObjectOutputStream(output)
oos.writeObject(p1)
oos.flush
oos.close

val input = new ByteArrayInputStream(output.toByteArray())
val ois = new ObjectInputStream(input)
val p2 = ois.readObject().asInstanceOf[Person]

assert(p2.name == "John")
assert(p2.age == 21)

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;

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()

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

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

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)

Creation

create some XML programmatically

Given the following CSV:

bread,3,2.50
milk,2,3.50

Produce the equivalent information in XML, e.g.:

<shopping>
<item name="bread" quantity="3" price="2.50" />
<item name="milk" quantity="2" price="3.50" />
</shopping>

clojure

(defn list->xml-item [lst]
(let [[name quantity price] (map str lst)]
{:tag :item
:attrs {:name name
:quantity quantity
:price price}}))

(defn cvs->xml [r]
(->> (map #(read-string (str "(" % ")")) (line-seq r))
(map list->xml-item)
(assoc {:tag :shopping} :content)
(emit)
(with-out-str)))

(println (cvs->xml *cvs-reader*))

cpp

string input("bread,3,2.50\nmilk,2,3.50\n");

tokenizer<char_separator<char> > tokens(input, char_separator<char>(", \n"));
tokenizer<char_separator<char> >::iterator it = tokens.begin();

xml_document<> doc;
xml_node<> *shopping = doc.allocate_node(node_element, "shopping");
doc.append_node(shopping);

while (it != tokens.end()) {
xml_node<> *item = doc.allocate_node(node_element, "item");
shopping->append_node(item);

item->append_attribute(doc.allocate_attribute("name", doc.allocate_string((*it++).c_str())));
item->append_attribute(doc.allocate_attribute("quantity", doc.allocate_string((*it++).c_str())));
item->append_attribute(doc.allocate_attribute("price", doc.allocate_string((*it++).c_str())));
}

cout << doc << endl;

fsharp

#r "System.Xml.dll"
#r "System.Xml.Linq.dll"

open System
open System.Xml
open System.Xml.Linq

let data = "bread,3,2.50
milk,2,3.50"

let X name =
XName.Get(name)

let lines = data.Split( [|"\n" |], StringSplitOptions.RemoveEmptyEntries)

let document = new XDocument()
let element = new XElement(X "shopping")
document.Add(element)

lines
|> Seq.iter (fun line ->
let items = line.Split([|','|])
let item = new XElement(X "item",
new XAttribute(X "name", items.[0]),
new XAttribute(X "quantity", items.[1]),
new XAttribute(X "price", items.[2]))
element.Add(item))

let output = document.ToString();;

groovy

b = new groovy.xml.MarkupBuilder()
b.shopping {
csv.eachLine { line ->
(n, q, p) = line.split(',')
item(name:n, quantity:q, price:p)
}
}

// Groovy equivalent of Java JAXB solution
@XmlAccessorType(NONE)
class Item {
@XmlAttribute String name
@XmlAttribute Integer quantity
@XmlAttribute Double price
}

@XmlAccessorType(NONE)
@XmlRootElement
class Shopping {
@XmlElement Set<Item> items = []
}

Shopping shopping = new Shopping()
csvtext.eachLine{ line ->
(n, q, p) = line.split(',')
shopping.items << new Item(name:n, quantity:q.toInteger(), price:p.toDouble())
}
JAXB.marshal shopping, System.out

java

// In this solution JAXB is used to created the xml output.
// JAXB is included in Java 1.6. Runs with 1.5 if you include JAXB Jars
// in the classpath.
class Item {
// Of course you use getters and setters and declare attributes private.
// In this sample a "dirty" way is chosen to keep LOC low.
@XmlAttribute
String name;
@XmlAttribute
Integer quantity;
@XmlAttribute
Double price;
}

@XmlRootElement
class Shopping {
@XmlElement
Set<Item> items = new HashSet<Item>();
}

String line = null;
Shopping shopping = new Shopping();
try {
BufferedReader reader = new BufferedReader(new FileReader("shopping.csv"));
while ((line = reader.readLine()) != null) {
String[] parts = line.split(",");
Item item = new Item();
item.name = parts[0];
item.quantity = Integer.parseInt(parts[1]);
item.price = Double.parseDouble(parts[2]);
shopping.items.add(item);

}
JAXB.marshal(shopping, "D:" + File.separatorChar + "shopping.auto.xml");
} catch (IOException e) {
e.printStackTrace();
}

ocaml

(* Compilation (native):
$ ocamlopt -I +csv csv.cmxa -I +xml-light xml-light.cmxa csv2xml.ml -o csv2xml
*)

let () =
let table = Csv.load "shopping.csv" in
let columns = ["name"; "quantity"; "price"] in

let xml = Xml.Element ("shopping", [],
List.rev (
List.fold_left (fun acc row ->
Xml.Element ("item",
List.combine columns row, []) :: acc) [] table)) in

print_endline (Xml.to_string_fmt xml)

python

from xml.dom import minidom

csv = """bread,3,2.50
milk,2,3.50"""

doc = minidom.Document()
shopping = doc.createElement("shopping")

for line in csv.split("\n"):
name, quantity, price = line.split(",")
el = doc.createElement("item")
el.setAttribute("name", name)
el.setAttribute("quantity", quantity)
el.setAttribute("price", price)
shopping.appendChild(el)

print shopping.toprettyxml()

from xml.etree.ElementTree import Element, SubElement, tostring

csv = """bread,3,2.50
milk,2,3.50"""

root = Element('shopping')

for line in csv.split("\n"):
name, quantity, price = line.split(",")
SubElement(root,'item', {'name' : name,
'quantity' : quantity,
'price' : price })

print tostring(root)

scala

<shopping>
{List("bread,3,2.50", "milk,2,3.50") map { row =>
row split ","
} map { item =>
<item name={item(0)} quantity={item(1)} price={item(2)}/>
}}
</shopping>

Algorithms

Geometry

Find all Pythagorean triangles with length or height less than or equal to 20

Pythagorean triangles are right angle triangles whose sides comply with the following equation:

a * a + b * b = c * c

where c represents the length of the hypotenuse, and a and b represent the lengths of the other two sides. Find all such triangles where a, b and c are non-zero integers with a and b less than or equal to 20. Sort your results by the size of the hypotenuse. The expected answer is:

[3, 4, 5]
[6, 8, 10]
[5, 12, 13]
[9, 12, 15]
[8, 15, 17]
[12, 16, 20]
[15, 20, 25]

clojure

(defn pythagorean [a b c] (= (+ (* a a) (* b b)) (* c c)))

(defn intsqrt [cc]
(. (. Math sqrt cc) intValue)
)

(defn triples [maxSize]
(filter not-empty
(for [a (range 1 20) b (range a 20)]
(let [c (intsqrt (+ (* a a) (* b b)))]
(if (pythagorean a b c)
[a b c]
()
)))))

(triples 20)
; -> ([3 4 5] [5 12 13] [6 8 10] [8 15 17] [9 12 15] [12 16 20] [15 20 25])

(defn sortByHypotenuse [triples]
(sort-by #(first (rest (rest %))) triples)
)

(sortByHypotenuse (triples 20))
; -> ([3 4 5] [6 8 10] [5 12 13] [9 12 15] [8 15 17] [12 16 20] [15 20 25])

(doseq [pt (sort-by #(% 2)
(for [a (range 1 21)
b (range a 21)
:let [aa+bb (+ (* a a) (* b b))
c (Math/round (Math/sqrt aa+bb))]
:when (= aa+bb (* c c))]
[a b c]))]
(println pt))

cpp

vector<solution> solutions;

for (int a = 1; a <= 20; ++a)
for (int b = a + 1; b <= 20; ++b)
{
int c_squared = a*a + b*b;
int c = b + 1;
while (c * c < c_squared)
++c;
if (c * c == c_squared)
solutions.push_back(make_tuple(a, b, c));
}

sort(begin(solutions), end(solutions),
[](const solution& s1, const solution& s2) { return get<2>(s1) < get<2>(s2); });

for (const auto &s: solutions)
cout << '[' << get<0>(s) << ", " << get<1>(s) << ", " << get<2>(s) << ']' << endl;

fsharp

let getGoodTri (a,b) =
let h = int(System.Math.Sqrt(float(a*a + b*b)))
if a*a + b*b = h*h then Some(a,b,h)
else None

seq{ for i in 1..20 do yield! seq{for j in i..20 do yield i,j} } |> Seq.choose(getGoodTri) |> Seq.sortBy(fun (_,_,c) -> c);;

groovy

Set results = []
for (x in 1..20)
for (y in x..20) {
def z = sqrt(x*x + y*y)
if (z.toInteger() == z) results << [x, y, z.toInteger()]
}
println results.sort{it[2]}.join('\n')

java

SortedSet<List<Integer>> results = new TreeSet<List<Integer>>(new Comparator<List<Integer>>() {
public int compare(List<Integer> o1, List<Integer> o2) {
return o1.get(2).compareTo(o2.get(2));
}
});
for (int x = 1; x <= 20; x++) {
for (int y = 1; y <= 20; y++) {
double z = Math.hypot(x, y) ;
if ((int) z == z)
results.add(Arrays.asList( new Integer[] { x, y, (int) z }));
}
}

ocaml

let is_int v =
v = (snd (modf v))

let sort_by_third tup =
let third (_,_,v) = v in
let cmp a b = compare (third a) (third b) in
List.sort cmp tup

let hypi ia ib =
let hyp a b = sqrt(a**2.0 +. b**2.0) in
hyp (float_of_int ia) (float_of_int ib)

let find_pythag max =
let rec py t = match t with
| (a,_) when a > max -> []
| (a,b) when b > max -> py (a+1,a+1)
| (a,b) ->
let next = (a,b+1) in
let cf = hypi a b in
if (is_int cf) then
( a,b,(int_of_float cf) ) :: (py next)
else
py next
in
sort_by_third ( py (1,1) )

python

from math import sqrt

a = 1
ret = []
while a <= 20:
b = 1
while b <= 20:
c = sqrt((a**2)+(b**2))
if int(c) == c and sorted([a,b,int(c)]) not in ret:
ret.append(sorted([a,b,int(c)]))
b +=1
a +=1
print ret

or if you wanna get snarky..

print sorted(set([tuple(sorted((a,b,int(sqrt((a**2)+(b**2)))))) for a in xrange(1,21) for \
b in xrange(1,21) if int(sqrt((a**2)+(b**2))) == sqrt((a**2)+(b**2))]))

scala

val res = for (
x <- 1 to 20 ;
y <- x to 20 ;
z = Math.sqrt(x*x + y*y) ;
if (z.toInt == z) )
yield (x, y, z.toInt)

res.toList.sortWith { (t1, t2) =>
t1._3 < t2._3
} foreach (println(_))

(for(x <- 1 to 20;
y<- x to 20;
z<- 1 to 30;
if(z*z == x*x + y*y)) yield(x, y, z)
).sortWith(_._3 < _._3) foreach println

( for (
a <- 1 to 20 ;
b <- a to 20 ;
c = math.sqrt( a*a + b*b )
if c.toInt == c
) yield ( a, b, c.toInt )
).sortBy {_._3} foreach println

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;
}

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))
}

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)
;;

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)

scala

def gcd(x: Int, y: Int): Int =
if (b == 0) x
else gcd(b, x % y)

Misc

Fun

produces a copy of its own source code

In computing, a quine is a computer program which produces a copy of its own source code as its only output.

clojure

(def s"(def s%s)(printf s(pr-str s))")(printf s(pr-str s))

cpp

#include <cstdio>
#define B(x) x; printf("{ B(" #x ") }\n");
int main()
{ B(printf("#include <cstdio>\n#define B(x) x; printf(\"{ B(\" #x \") }\\n\");\nint main()\n")) }

fsharp

(fun s -> printf "%s %s" s s) "(fun s -> printf \"%s %s\" s s)"

groovy

s="s=%s;printf s,s.inspect()";printf s,s.inspect()

evaluate s='char q=39;print"evaluate s=$q$s$q"'

s="s=%c%s%c;printf s,34,s,34";printf s,34,s,34

s='s=%c%s%1$c;printf s,39,s';printf s,39,s

printf _='printf _=%c%s%1$c,39,_',39,_

java

public class Quine {public static void main(String[] args) {String s = "public class Quine {public static void main(String[] args) {String s = %c%s%c;System.out.printf(s, 34, s, 34);}}";System.out.printf(s, 34, s, 34);}}

public class Quine {
public static void main(String[] args) {
Character cq = (char) 34;
Character cn = (char) 10;
Character cs = (char) 92;
String s = "public class Quine {\n public static void main(String[] args) {\n Character cq = (char) 34;\n Character cn = (char) 10;\n Character cs = (char) 92;\n String s = %c%s%c;\n System.out.printf(s, cq, s.replace(cn.toString(), cs.toString() + 'n'), cq);\n }\n}";
System.out.printf(s, cq, s.replace(cn.toString(), cs.toString() + 'n'), cq);
}
}

ocaml

(fun s -> Printf.printf "%s %S" s s) "(fun s -> Printf.printf \"%s %S\" s s)"

(fun p -> Printf.printf p (string_of_format p)) "(fun p -> Printf.printf p (string_of_format p)) %S"

python

# adapted from a Quine by Sean B. Palmer

print (lambda s='print (lambda s=%r: (s %% s))()': (s % s))()

x='x=%r;print(x%%x)';print(x%x)

scala

val s="val s=%c%s%c; printf(s, 34, s, 34)"; printf(s, 34, s, 34)

Parallel

Threads

Create a multithreaded "Hello World"

Create a program which outputs the string "Hello World" to the console, multiple times, using separate threads or processes.

Example:

-Output-

Thread one says Hello World!
Thread two says Hello World!
Thread four says Hello World!
Thread three says Hello World!

-Notice that the threads can print in any order.

clojure

(doseq [msg ["one" "two" "three" "four"]]
(future (println "Thread" msg "says Hello World!")))

(dorun (pmap #(println (str "Thread " % " says Hello World!")) '("one" "two" "three" "four")))

(dorun (map (fn [n] (.start (Thread. #(println (str "Thread " n " says Hello World!")))))
'("one" "two" "three" "four")))

cpp

#include <iostream>
#include <string>

using namespace std;

int main(){
int pid;
string text[4]={"one","two","three","four"};
for (int i=0;i<4;i++){
pid=fork();
if (pid>0){
//cout << "Process("<<pid<<") - " << "Thread " << text[i] << " says Hello World!" << endl;
cout << "Thread " << text[i] << " says Hello World!" << endl;
exit(0);
}
}
return 0;
}

#include <iostream>
#include <string>

#include <omp.h>

int main() {
unsigned int const num_threads = 4;

std::string const names[] = { "one", "two", "three", "four" };

# pragma omp parallel num_threads(num_threads)
{
unsigned const id = omp_get_thread_num();
// Stream concatenation isn't thread-safe so we use a critical section.
# pragma omp critical
std::cout << "Thread " << names[id] << " says Hello World!" << std::endl;
}
}

fsharp

let mappedString =
["Thread one says Hello World!";
"Thread two says Hello World!";
"Thread four says Hello World!";
"Thread three says Hello World!"]
|> Seq.map (fun str -> async { printfn "%s" str })

Async.RunSynchronously (Async.Parallel mappedString)

groovy

["one","two","three","four"].each { tid ->
Thread.start {
println "Thread $tid says Hello World!"
}
}

import static groovyx.gpars.Parallelizer.*
withParallelizer {
["one","two","three","four"].eachParallel {
println "Thread $it says Hello World!"
}
}

java

for (int i = 0; i < 4; i++) {
final int nr = i ;
new Thread(new Runnable() {
public void run() {
System.out.println("Thread " + new String[] { "one", "two", "three", "four" }[nr] + " says Hello World!");
}
}).start();
}

ocaml

(* Compilation (native):
$ ocamlopt -thread unix.cmxa threads.cmxa threads_hello.ml -o threads_hello
*)

let say_hello (i, msg) =
Printf.printf "Thread %d says %s\n" i msg
;;
let thread_ids = Array.init 4 (fun i ->
Thread.create say_hello (i, "Hello World!")) in
Array.iter Thread.join thread_ids;
flush_all ()

python

#!/usr/bin/python
from threading import Thread
Nthread = ['one','two','three','four']
def ThreadSpeaks(number):
print "Thread", number, "says Hello World!"
if __name__ == "__main__":
for n in range(0,len(Nthread)):
th =Thread(target=ThreadSpeaks, args=(Nthread[n],))
th.start()

scala

import scala.actors.Actor

List("one", "two", "three", "four").foreach { name =>
new Actor { override def act() = { println("Thread " + name + " says Hello World!") } }.start
}

List("one", "two", "three", "four").foreach { name =>
new Thread { override def run() = { println("Thread " + name + " says Hello World!") } }.start
}

import scala.actors.Futures._
List("one", "two", "three", "four").foreach(name => future(println("Thread " + name + " says hi")))

Create read/write lock on a shared resource.

Create multiple threads or processes who are either readers or writers. There should be more readers then writers.

(From Wikipedia):

Multiple readers can read the data in parallel but an exclusive lock is needed while writing the data. When a writer is writing the data, readers will be blocked until the writer is finished writing.

Example:

-Output-

Thread one says that the value is 8.
Thread three says that the value is 8.
Thread two is taking the lock.
Thread four tried to read the value, but could not.
Thread five tried to write to the value, but could not.
Thread two is changing the value to 9.
Thread two is releasing the lock.
Thread four says that the value is 9.
...

--Notice that when a needed resource is locked, a thread can set a timer and try again in the future, or wait to be notified that the resource is no longer locked.

clojure

; NOTE! Using explicit locking is NOT the Clojure way. It was done
; this way in order to comply exactly with the problem
; specification. Sharing data in Clojure would normally be done by
; using "atom", "agent" or "ref" depending on situation. None of those
; methods would ever result in the reader not being able to read (as
; required by the problem) since reading is wait-free in clojure.

(def *readers* (map #(agent %) '("one" "two" "three")))
(def *writers* (map #(agent %) '("four" "five")))
(def *mutex* (agent :unlocked))
(def *value* 0)

; mutex implementation
(defn lock [state who success-fn fail-fn]
(send who (if (= state :locked) fail-fn success-fn))
:locked)

(defn unlock [mutex]
:unlocked)

; Must be invoked with send-off since this handler blocks
(defn rand-sleep [state next-fn]
(Thread/sleep (rand-int 5))
(send *agent* next-fn)
state)

; Reader functions
(declare try-read)

(defn reader-got-lock [name]
(println (format "Thread %s says that the value is %d." name *value*))
(send *mutex* unlock)
(send-off *agent* rand-sleep try-read)
name)

(defn reader-did-not-get-lock [name]
(println (format "Thread %s tried to read the value, but could not." name))
(send-off *agent* rand-sleep try-read)
name)

(defn try-read [name]
(send *mutex* lock *agent* reader-got-lock reader-did-not-get-lock)
name)

; Writer functions
(declare try-write)

(defn writer-got-lock [name]
(println (format "Thread %s is taking the lock." name))
(def *value* (rand-int 10))
(println (format "Thread %s is changing the value to %d." name *value*))
(send *mutex* unlock)
(println (format "Thread %s is relasing the lock." name))
(send-off *agent* rand-sleep try-write)
name)

(defn writer-did-not-get-lock [name]
(println (format "Thread %s tried to write the value, but could not." name))
(send-off *agent* rand-sleep try-write)
name)

(defn try-write [name]
(send *mutex* lock *agent* writer-got-lock writer-did-not-get-lock)
name)

(dorun (map #(send % try-write) *writers*))
(dorun (map #(send % try-read) *readers*))

cpp

class reader
{
string name_;
public:
reader(const string& name) : name_(name) {}

void operator()() {
for (;;this_thread::sleep(posix_time::milliseconds(1)))
{
shared_lock<shared_mutex> lock(m, try_to_lock);
lock_guard<mutex> cout_lock(io_m);
cout << "Thread " << name_;
if (lock)
cout << " says that the value is " << shared_value << "." << endl;
else
cout << " tried to read the value, but could not." << endl;
}
}
};

class writer
{
string name_;
public:
writer(const string& name) : name_(name) {}
void operator()() {
for (;;this_thread::sleep(posix_time::milliseconds(1)))
{
unique_lock<shared_mutex> lock(m, try_to_lock);
lock_guard<mutex> cout_lock(io_m);
cout << "Thread " << name_;
if (lock)
{
cout << " is taking the lock." << endl;
shared_value = rand() % 10;
cout << "Thread " << name_ << " is changing the value to " << shared_value << endl;
cout << "Thread " << name_ << " is releasing the lock. " << endl;
}
else
cout << " tried to write to the value, but could not." << endl;
}
}
};

int main()
{
thread t1 = thread(reader("one"));
thread t2 = thread(reader("two"));
thread t3 = thread(reader("three"));
thread t4 = thread(writer("four"));
writer("five")();
}

fsharp

open System.Threading
let lock = new ReaderWriterLock()
let mutable value = 0
let lockTimeout = 1

let ReaderThread t =
let random = new System.Random()
for i in 0 .. 100 do
try
lock.AcquireReaderLock(lockTimeout)
try
printfn "Thread %i says that the value is %i" t value
finally
lock.ReleaseReaderLock()
with _ ->
printfn "Thread %i tried to read the value, but could not (timeout)." t
Thread.Sleep(random.Next(50))

let WriterThread t =
let random = new System.Random()
for i in 0 .. 100 do
try
lock.AcquireWriterLock(lockTimeout)
try
value <- random.Next(10)
printfn "Thread %i is changing the value to %i" t value
Thread.MemoryBarrier()
finally
lock.ReleaseWriterLock()
printfn "Thread %i is releasing the lock." t
with _ ->
printfn "Thread %i tried to write the value, but could not (timeout)." t
Thread.Sleep(random.Next(50))

[| 0 .. 20 |]
|> Array.iter (fun t ->
async {
if t % 3 = 0 then
WriterThread t
else
ReaderThread t
}
|> Async.Start
)

groovy

def lock = new ReentrantLock()
Integer value = 8

20.times { i ->
if (i % 3 == 0) {
Thread.start {
if (!lock.tryLock()) {
println "Thread " + i + " tried to write the value, but could not."
lock.lock()
}
value = (int) (Math.random() * 10)
println "Thread " + i + " is changing the value to " + value
lock.unlock()
println "Thread " + i + " is releasing the lock."
}
} else {
Thread.start {
if (!lock.tryLock()) {
println "Thread " + i + " tried to read the value, but could not."
lock.lock()
}
println "Thread " + i + " says that the value is " + value + "."
lock.unlock()
}
}
}

java

public class ParallelPermutations {

Lock lock = new ReentrantLock();

Integer value = 8;

public static void main(String[] args) {
new ParallelPermutations(Arrays.asList(args));
}

public ParallelPermutations(List<String> words) {
for (int i = 0; i < 20; i++) {
final Integer cnt = i ;
if ( i % 3 == 0) {
new Thread(new Runnable() {
public void run() {
if ( ! lock.tryLock() ) {
System.out.println("Thread " + cnt + " tried to write the value, but could not.") ;
lock.lock();
}
value = (int) (Math.random() * 10);
System.out.println("Thread " + cnt + " is changing the value to " + value ) ;
lock.unlock();
System.out.println("Thread " + cnt + " is releasing the lock.") ;
}
}).start();
} else {
new Thread(new Runnable() {
public void run() {
if ( ! lock.tryLock() ) {
System.out.println("Thread " + cnt + " tried to read the value, but could not.") ;
lock.lock() ;
}
System.out.println("Thread " + cnt + " says that the value is " + value + ".") ;
lock.unlock();
}
}).start();
}
}
}
}

ocaml

(* Compilation (native):
$ ocamlopt -thread unix.cmxa threads.cmxa threads_lock.ml -o threads_lock
*)

let value = ref 8
let mutex = Mutex.create ()

let create_writer i =
if not (Mutex.try_lock mutex) then begin
Printf.printf "Thread %d tried to write the value but could not.\n" i;
Mutex.lock mutex
end;
value := Random.int 10;
Printf.printf "Thread %d is changing the value to %d\n" i !value;
Mutex.unlock mutex;
Printf.printf "Thread %d is releasing the lock.\n" i

let create_reader i =
if not (Mutex.try_lock mutex) then begin
Printf.printf "Thread %d tried to read the value but could not.\n" i;
Mutex.lock mutex
end;
Printf.printf "Thread %d says that the value is %d\n" i !value;
Mutex.unlock mutex
;;

let thread_ids = Array.init 20 (fun i ->
Thread.create (if i mod 3 == 0 then create_writer else create_reader) i) in
Array.iter Thread.join thread_ids

python

#!/usr/bin/python
from threading import Thread, Lock
import time
thread_readers = ['one','two','three']
thread_writer = ['four','five']
lock = Lock()
value = 0

def Threadread(number):
global value
while True:
if lock.acquire(False):
print "Thread", number, "is taking the lock"
value += 1
print "Thread", number, "is changing the value to", value
print "Thread", number, "is releasing the lock."
lock.release()
else:
print "Thread", number, "tried to write to the value, but could not."
def Threadwrite(number):
global value
while True:
if lock.acquire(False):
print "Thread", number ,"four says that the value is", value
else:
print "Thread", number ,"tried to read the value, but could not."
if __name__ == "__main__":
for n in range(0,len(thread_readers)):
th =Thread(target=Threadread, args=(thread_readers[n],))
th.start()
for n in range(0,len(thread_writer)):
th =Thread(target=Threadwrite, args=(thread_writer[n],))
th.start()

scala

import java.util.concurrent.locks.ReentrantReadWriteLock
import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock
import scala.util.Random

class Reader(name: String, lock: ReadLock) extends Thread {
override def run() = {
println(name)
while (true) {
if (!lock.tryLock)
{
println("Thread " + name + " tried to read the value, but could not.")
lock.lock
}
println("Thread " + name + " says that the value is " + rwLockOnSharedResource.value)
lock.unlock
Thread.sleep(3) // Generates output more similar to the problem description
}
}
}

class Writer(name: String, lock: WriteLock) extends Thread {
override def run() = {
while (true) {
if (!lock.tryLock) {
println("Thread " + name + " tried to write the value, but could not.")
lock.lock
}
println("Thread " + name + " is taking the lock.")
rwLockOnSharedResource.value = rwLockOnSharedResource.nextValue
println("Thread " + name + " is changing the value to " + rwLockOnSharedResource.value)
lock.unlock
println("Thread " + name + " is releasing the lock.")
Thread.sleep(3) // Generates output more similar to the problem description
}
}
}

object rwLockOnSharedResource {
private val maxValue = 10
private val randomVal = new Random
var value = nextValue

def nextValue = randomVal.nextInt(maxValue)

def main(args: Array[String]) = {
val rwLock = new ReentrantReadWriteLock(true)
val threadNames = List("one", "two", "three", "four", "five")
val readerCnt = threadNames.length * 2 / 3
val readerNames = threadNames.take(readerCnt)
val writerNames = threadNames.drop(readerCnt)

readerNames.foreach(new Reader(_, rwLock.readLock).start)
writerNames.foreach(new Writer(_, rwLock.writeLock).start)
}
}