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Solved Problems

Strings

Printing

Output a string to the console

Write the string "Hello World!" to STDOUT

clojure

(println "Hello World!")

cpp

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

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

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

erlang

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

fantom

echo("Hello World!")

fsharp

printfn "Hello World!"

groovy

println "Hello World!"

haskell

main = putStrLn "Hello World!"

ocaml

print_string "Hello world!\n";;

print_endline "Hello world!";;

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

python

print "Hello World!"

ruby

puts "Hello World!"

$stdout<<"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();

erlang

% encode ampersand in your string using %XX where XX is hex code for ampersand
% optionally encode spaces for completeness sake to keep URL solid
URL = "http://myserver.com/custinfo/edit.php?mode=view&fname=Ron%20%26%20Jean&lname=Smith",
{_, Query} = string:tokens(URL, "?"),
KeyValuePairs = string:tokens(Query, "&"),...

fantom

encoded := `http://myserver.com/custinfo/edit.php`.plusQuery(
["fname":"Ron & Jean", "lname":"Smith"]).encode
echo(encoded)

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")

haskell

import Network.CGI

query = "http://myserver.com/custinfo/edit.php?" ++ formEncode [("mode", "view"), ("fname", "Ron & Jan"), ("lname","Smith")]

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'.

ruby

gem 'uri-query_params'
require 'uri/query_params'

url = URI("http://myserver.com/custinfo/edit.php?mode=view&fname=Ron%20&%20Jean&lname=Smith")
url.query_params['fname']
# => "Ron & Jean"

url = "http://myserver.com/custinfo/edit.php?mode=view&fname=Ron & Jean&lname=Smith"
url = URI.parse(URI.encode(url))

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

erlang

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

fantom

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

fsharp

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

groovy

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

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

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

haskell

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

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

ocaml

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

python

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

ruby

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

scala

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

Define a multiline string

Define the string:

"This

Is

A

Multiline

String"

clojure

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

cpp

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

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

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

erlang

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

fantom

s := "This
Is
A
Multiline
String"

fsharp

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

let multiline = "This
Is
A
Multiline
String"

groovy

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

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

haskell

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

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"
)

ruby

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

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

scala

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

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

Define a string containing variables and expressions

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

clojure

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

cpp

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

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

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

erlang

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

fantom

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

fsharp

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

groovy

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

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

haskell

import Text.Printf

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

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

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)

ruby

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

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

scala

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

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

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

Manipulation

Reverse the characters in a string

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

clojure

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

(apply str (reverse "reverse me"))

cpp

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

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

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

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

erlang

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

Reversed = revchars("reverse me"),

fantom

"reverse me".reverse

fsharp

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

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

groovy

reversed = "reverse me".reverse()

haskell

reverse "reverse me"

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]

ruby

puts "reverse me".reverse

scala

val reversed = "reverse me".reverse

Reverse the words in a string

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

clojure

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

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

cpp

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

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

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

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

erlang

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

fantom

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

fsharp

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

groovy

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

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

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

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

haskell

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

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()))

ruby

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

scala

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

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

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

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

Text wrapping

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

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

clojure

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

cpp

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

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

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

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

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

int main()
{
stringstream input;

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

erlang

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

fantom

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

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

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

fsharp

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

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

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

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

groovy

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

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

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

haskell

import Data.List (intercalate)

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

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

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

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

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="> ")

ruby

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

scala

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

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

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

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

Remove leading and trailing whitespace from a string

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

clojure

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

(clojure.string/trim " hello ")

(.trim " hello ")

cpp

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

erlang

Trimmed = string:strip(S),

fantom

s := " hello ".trim

fsharp

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

let trimmed = " hello ".Trim()

groovy

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

haskell

unwords (words " hello ")

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()

ruby

puts " hello ".strip

" 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;
}

erlang

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

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

fantom

rot := |Str s, |Int c -> Int| remap -> Str|
{
rs := ""
s.each { rs += remap(it).toChar }
return rs
}

rot13 := |Str s -> Str|
{
rot(s) |Int c -> Int|
{
lc := c.lower
c += (lc >= 'a' && lc <= 'm') ? 13
: ((lc >= 'n' && lc <= 'z') ? -13 : 0)
return c
}
}

rot47 := |Str s -> Str|
{
rot(s) |Int c -> Int|
{
c += (c >= '!' && c <= 'O') ? 47
: ((c >= 'P' && c <= '~') ? -47 : 0)
return c
}
}

s := "Hello World #123"
echo("s=$s")
echo("rot13=${rot13(s)}")
echo("rot47=${rot47(s)}")

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'

haskell

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')

ruby

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

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);

erlang

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

fantom

s := "Space Monkey".localeUpper

fsharp

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

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

groovy

println "Space Monkey".toUpperCase()

haskell

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

toUpperCase "Space Monkey" ""

toUpperCase = map Char.toUpper

toUpperCase "Space Monkey"

ocaml

String.uppercase "Space Monkey";;

python

"Space Monkey".upper()

ruby

uppper = text.upcase

scala

println("Space Monkey".toUpperCase)

Make a string lowercase

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

clojure

(.toLowerCase "Caps ARE overRated")

cpp

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

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

erlang

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

fantom

s := "Caps ARE overRated".localeLower

fsharp

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

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

groovy

println "Caps ARE overRated".toLowerCase()

haskell

import Char
str = map toLower "Caps ARE overRated"

ocaml

String.lowercase "Caps ARE overRated";;

python

"Caps ARE overRated".lower()

ruby

"Caps ARE overRated".downcase

scala

"Caps ARE overRated".toLowerCase

Capitalise the first letter of each word

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

clojure

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

cpp

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

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

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

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

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

erlang

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

fantom

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

fsharp

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

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

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

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

groovy

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

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

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

haskell

import Data.Char

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

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()

ruby

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

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

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

scala

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

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

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

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

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

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

Numbers

Mathematical

Find the distance between two points

clojure

(defstruct point :x :y)

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

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

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

(distance [2 2] [3 3])

cpp

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

erlang

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

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

fantom

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

distance(px1, py1, px2, py2)

fsharp

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

groovy

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

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

haskell

data Floating n => Point2 n = Point2 n n

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

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

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)

ruby

# the hypotenuse sqrt(x**2+y**2)
distance = Math.hypot(x2-x1,y2-y1)

scala

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

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

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

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

Output

Zero pad a number

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

clojure

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

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

(format "%08d" 42)

cpp

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

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

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

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

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

erlang

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

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

fantom

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

formatted := 42.toLocale("00000000")

fsharp

printfn "%08d" 42

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

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

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

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

groovy

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

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

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

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

haskell

import Text.Printf

printf "%08d" 42

ocaml

Printf.printf "%08d" 42;;

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

python

"%08d" % 42

ruby

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

"%08d" % 42

scala

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

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

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

Right Space pad a number

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

clojure

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

cpp

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

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

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

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

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

erlang

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

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

fantom

formatted := 1024.toStr.padr(6)

fsharp

printfn "%-6d" 1024

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

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

groovy

println 1024.toString().padRight(6)

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

haskell

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

import Text.Printf

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

ocaml

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

python

"%-6s" % 1024

str(1024).rjust(6)

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

ruby

1024.to_s.ljust(6)

scala

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

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

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

Format a decimal number

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

clojure

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

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

cpp

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

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

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

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

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

erlang

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

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

fantom

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

fsharp

printfn "%3.2f" (0.7 / 0.8)

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

groovy

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

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

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

haskell

import Text.Printf

printf "%3.2f" (7/8)

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

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)

ruby

(7.0/8.0*100).round/100.0

(7.0/8.0).round(2)

scala

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

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

Left Space pad a number

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

clojure

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

cpp

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

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

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

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

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

erlang

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

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

fantom

formatted := 73.toStr.padl(10)

fsharp

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

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

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

groovy

println 73.toString().padLeft(10)

printf "%10d\n", 73

haskell

import Text.Printf

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

ocaml

Printf.printf "%10d" 73;;

python

"%10s" % 73

ruby

73.to_s.rjust(10)

scala

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

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

Random

Generate a random integer in a given range

Produce a random integer between 100 and 200 inclusive

clojure

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

cpp

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

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

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

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

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

unsigned rnd = generator();

erlang

RandomInt = gen_rand_integer(100, 200),

fantom

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

fsharp

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

groovy

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

haskell

import System.Random

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

main = randInRange 100 200 >>= print

import System.Random

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

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)

ruby

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

scala

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

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

Generate a repeatable random number sequence

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

clojure

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

cpp

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

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

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

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

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

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

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

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

erlang

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

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

fantom

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

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

fsharp

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

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

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

groovy

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

haskell

import System.Random
import Control.Monad (forM_)

main = do
printRands
printRands

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

import System.Random

gen1 = mkStdGen 12345
gen2 = mkStdGen 12345

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

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)

ruby

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

scala

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

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

Regex

Matching

Check if a string matches a regular expression

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

clojure

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

cpp

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

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

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

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

erlang

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

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

fantom

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

fsharp

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

groovy

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

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

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

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

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

haskell

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

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'

ruby

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

scala

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

Check if a string matches with groups

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

clojure

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

cpp

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

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

erlang

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

fantom

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

fsharp

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

groovy

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

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

haskell

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

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)

ruby

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

scala

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

Searching

Check if a string contains a match to a regular expression

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

clojure

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

cpp

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

erlang

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

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

fantom

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

fsharp

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

groovy

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

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

haskell

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

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'

ruby

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

scala

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

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

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

clojure

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

cpp

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

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

erlang

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

fantom

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

fsharp

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

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

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

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

groovy

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

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

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

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

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

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

haskell

import Text.Regex

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

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

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"))

ruby

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

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

scala

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

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

Lists

Declaration

Define an empty list

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

clojure

(list)

'()

cpp

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

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

erlang

List = [],

fantom

list := [,]

fsharp

let list = []

let list = List.empty

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

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

groovy

list = []

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

haskell

let list = []

ocaml

let list = [];;

python

list = []

ruby

list = []

list = Array.new

scala

val list = Nil

val list = List()

val list : List[String] = List()

Define a static list

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

clojure

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

cpp

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

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

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

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

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

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

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

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

erlang

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

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

fantom

list := ["One", "Two", "Three", "Four", "Five"]

fsharp

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

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

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

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

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

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

groovy

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

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

haskell

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

ocaml

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

python

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

ruby

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

list = %w(One Two Three Four Five)

scala

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

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

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

Output

Join the elements of a list, separated by commas

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

clojure

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

cpp

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

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

erlang

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

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

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

fantom

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

fsharp

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

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

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

groovy

string = fruit.join(', ')

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

haskell

import Data.List

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

ocaml

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

python

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

ruby

string = fruit.join(', ')

scala

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

val result = fruit.mkString(",")

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

Join the elements of a list, in correct english

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

clojure

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

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

cpp

Console::WriteLine(join(fruit));

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

erlang

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

% ------

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

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

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

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

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

fantom

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

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

fsharp

groovy

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

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

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

haskell

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

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(*[]) == ""

ruby

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

scala

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

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

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

Produce the combinations from two lists

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

clojure

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

(mapcat (fn [x] (map #(list % x) ["a", "b", "c"])) [4, 5])

cpp

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

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

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

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

cout << combo << endl;

erlang

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

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

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

fantom

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

fsharp

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

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

groovy

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

haskell

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

main = mapM_ print comb

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

main = print comb

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])]

ruby

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

scala

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

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

// ------

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

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

From a List Produce a List of Duplicate Entries

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

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

clojure

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

cpp

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

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

cout << dups << endl;

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

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

erlang

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

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

fantom

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

fsharp

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

groovy

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

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

assert output == ["bob"]

haskell

import Data.List

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

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]

ruby

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

scala

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

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

Access

Fetch an element of a list by index

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

clojure

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

cpp

String^ result = list[2];

erlang

Result = lists:nth(3, List),

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

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

Result = nth0(2, List),

fantom

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

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

fsharp

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

groovy

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

haskell

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

ocaml

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

python

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

ruby

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

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

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

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

scala

val result = list(2)

Fetch the last element of a list

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

clojure

(last '[One Two Three Four Five])

cpp

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

string last_elem = lst.back();

erlang

Result = lists:last(List),

Result = last(List),

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

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

fantom

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

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

fsharp

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

// ------

let result = last list

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

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

groovy

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

haskell

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

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]

ruby

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

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

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

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

scala

val result = list.last

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

Find the common items in two lists

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

clojure

(use 'clojure.set)

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

cpp

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

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

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

erlang

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

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

fantom

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

fsharp

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

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

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

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

groovy

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

haskell

import Data.List

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

main = print (intersect beans colors)

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)

ruby

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

scala

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

Display the unique items in a list

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

clojure

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

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

cpp

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

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

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

erlang

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

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

fantom

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

fsharp

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

groovy

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

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

haskell

import Data.List

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

uniqueAges = nub ages

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))

ruby

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

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

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

scala

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

Modification

Remove an element from a list by index

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

clojure

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

cpp

fruit->RemoveAt(0);

erlang

Result = tl(List),

[_|Result] = List,

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

Result = drop(1, List),

fantom

list := ["Apple", "Banana", "Carrot"]
list.removeAt(0)

fsharp

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

// ------

let (_, right) = split_at fruit 0

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

// ------

let result = (drop fruit 1)

groovy

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

// mutate original list
list.remove(0)

haskell

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

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

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

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

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

ruby

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

fruit.delete_at(0)

scala

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

fruit = fruit.tail

fruit = fruit.drop(1)

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

Remove the last element of a list

clojure

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

cpp

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

erlang

Result = init(List),

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

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

fantom

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

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

fsharp

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

// ------

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

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

// ------

let result = (but_last fruit)

groovy

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

haskell

ages = [1,2,3,4]

init ages

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()

ruby

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

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

scala

fruit = fruit.init

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

Rotate a list

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

clojure

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

cpp

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

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

erlang

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

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

fantom

list := ["apple", "orange", "grapes", "bananas"]
list.add(list.removeAt(0))

fsharp

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

// ------

let result = (rotate fruit 1)

groovy

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

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

items = items + items.remove(0)

haskell

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

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

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))

ruby

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

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

scala

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

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

Manipulation

Gather together corresponding elements from multiple lists

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

clojure

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

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

(println (gatherer [firstnames lastnames years]))

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

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

cpp

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

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

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

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

erlang

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

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

fantom

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

echo(r)

fsharp

let result = (List.zip3 first last years)

groovy

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

haskell

import Prelude hiding (last)

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

actors = zip3 first last years

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)

ruby

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

result = first.zip(last, years)

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

result = [first, last, years].transpose

scala

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

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

// ------

val result = zip3(first, last, years)

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

List Combinations

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

clojure

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

cpp

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

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

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

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

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

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

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

erlang

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

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

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

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

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

fantom

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

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

fsharp

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

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

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

// ------

let cards = product suites faces

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

groovy

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

haskell

import Data.List

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

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

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

ruby

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

scala

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

// ------

val cards = product(suites, faces)

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

Perform an operation on every item of a list

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

clojure

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

cpp

list<string> words;

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

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

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

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

erlang

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

fantom

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

fsharp

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

groovy

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

haskell

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

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']]

ruby

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

scala

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

Split a list of things into numbers and non-numbers

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

clojure

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

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

(println (numberNonNumberSorter jumble))

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

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

cpp

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

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

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

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

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

#include <iostream>
#include <list>

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

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

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

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

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

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

erlang

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

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

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

fantom

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

fsharp

groovy

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

haskell

import Data.List (partition)

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

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

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

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)

ruby

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

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

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

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

scala

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

Testing

Test if a condition holds for all items of a list

Given a list, test if a certain logical condition (i.e. predicate) holds for all items of the list.

clojure

(every? #(> % 1) [2 3 4])

cpp

template <typename InputIterator, typename Predicate>
bool match_all(InputIterator first, InputIterator last, Predicate pred)
{
return find_if(first, last, !pred(_1)) == last;
}

erlang

Result = lists:all(Pred, List).

fantom

echo([2,3,4].all{ it>1 })

fsharp

let rec IsAll predicate source =
let mutable acc = true
for e in source do
acc <- acc && (predicate e)
acc

groovy

[2,3,4].every{it > 1}

haskell

all (> 1) [2, 3, 4]

ocaml

(* from the interactive loop *)
# List.for_all (fun x -> x > 1) [2; 3; 4] ;;
- : bool = true

python

all(x > 1 for x in [2,3,4])

ruby

[2, 3, 4].all? { |x| x > 1 }

scala

List(2, 3, 4).forall { _ > 1 }

List(2, 3, 4).forall { x => x > 1 }

Test if a condition holds for any items of a list

Given a list, test if a certain logical condition (i.e. predicate) holds for any items of the list.

clojure

; The standard library in Clojure has "not-any?" but (oddly enough) no "any?"
(defn any? [pred coll]
((complement not-any?) pred coll))

(any? #(> % 3) [2 3 4])

(some #(> % 3) [2 3 4])

cpp

template <typename InputIterator, typename Predicate>
bool match_any(InputIterator first, InputIterator last, Predicate pred)
{
return find_if(first, last, pred) != last;
}

erlang

Result = lists:any(Pred, List).

fantom

echo([2,3,4].any{ it==4 })

fsharp

let rec IsAny predicate source =
match source with
| [] -> false
| h::t ->
if (predicate h) then true
else (IsAny predicate t )

groovy

[2,3,4].any{it > 3}

haskell

any (> 1) [1, 2, 3]

ocaml

(* from the interactive loop: *)
# List.exists (fun x -> x > 3) [2; 3; 4] ;;
- : bool = true

python

any(x > 3 for x in [2, 3, 4])

ruby

[2, 3, 4].any? { |x| x > 3 }

scala

List(2, 3, 4).exists { _ > 3 }

List(2, 3, 4).exists { x => x > 3 }

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;

erlang

Map = dict:new(),

Map = orddict:new(),

Map = gb_trees:empty(),

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

fantom

map := [:]

fsharp

let map = Map.empty

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

let map = new Hashtable()

groovy

def map = [:]

Map map = new HashMap();

haskell

import qualified Data.Map as M

emptyMap = M.empty

ocaml

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

let m = Hashtbl.create 42

python

map = {}

ruby

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;

erlang

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

fantom

map := [:].ro

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()

haskell

import qualified Data.Map as Map

output :: Map.Map k v
output = Map.empty

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()

ruby

map = {}.freeze

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;

erlang

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

Map0 = dict:new(),

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

Map0 = gb_trees:empty(),

Map1 = gb_trees:enter(circle, 1, Map0),
Map2 = gb_trees:enter(triangle, 3, Map1),
Map3 = gb_trees:enter(square, 4, Map2),

Map = gb_trees:from_orddict(lists:keysort(1, [{circle, 1}, {triangle, 3}, {square, 4}])),

Map = ets:new(the_map_name, [ordered_set, private, {keypos, 1}]),
ets:insert(Map, [{circle, 1}, {triangle, 3}, {square, 4}]),

fantom

map := ["circle":1, "triangle":2, "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

haskell

import qualified Data.Map as M

initialMap = M.fromList [("circle", 1), ("triangle", 3), ("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}

ruby

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

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

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

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;

erlang

dict:is_key(mary, Pets) andalso begin io:format("ok~n"), true end.

IsMember = ets:member(Pets, mary), if (IsMember) -> io:format("ok~n") ; true -> false end.

case gb_trees:lookup(mary, Pets) of none -> false ; _ -> io:format("ok~n") end.

fantom

map := ["joe":"cat", "mary":"turtle", "bill":"canary"]
if (map.containsKey("mary")) echo("ok")

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'

haskell

import qualified Data.Map as M
import Control.Monad (when)

pets = M.fromList [("joe", "cat"), ("mary", "turtle"), ("bill", "canary")]

checkMary = when (M.member "mary" pets) (print "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"

ruby

puts "ok" if map.has_key?('mary')

puts "ok" if map['mary'] # Only works if map entry can't be nil or false

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;

erlang

dict:is_key(joe, Pets) andalso begin io:format("~w~n", [dict:fetch(joe, Pets)]), true end.

case dict:find(joe, Pets) of error -> false ; {ok, Pet} -> io:format("~w~n", [Pet]) end.

IsMember = ets:member(Pets, joe), if (IsMember) -> io:format("~w~n", [ets:lookup_element(Pets, joe, 2)]) ; true -> false end.

case ets:match(Pets, {joe, '$1'}) of [] -> false ; [[Pet]] -> io:format("~w~n", [Pet]) end.

case gb_trees:lookup(joe, Pets) of none -> false ; {value, Pet} -> io:format("~w~n", [Pet]) end.

fantom

map := ["joe":"cat", "mary":"turtle", "bill":"canary"]
pet := map["joe"]
echo("pet=$pet")

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'

haskell

import qualified Data.Map as M

pets = M.fromList [("joe", "cat"), ("mary", "turtle"), ("bill", "canary")]
retrieve = print $ M.findWithDefault "Not found" "joe" pets

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']

ruby

puts map['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";

erlang

Pets1 = dict:store(rob, dog, Pets0).

ets:insert(Pets, {rob, dog}).

Pets1 = gb_trees:enter(rob, dog, Pets0).

fantom

map["rob"] = "dog"

fsharp

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

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

groovy

pets['rob'] = 'dog'

pets.rob = 'dog'

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

haskell

import qualified Data.Map as M

pets = M.insert "rob" "dog" M.empty

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'

ruby

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);
}

erlang

Pet = dict:fetch(bill, Pets0), Pets1 = dict:erase(bill, Pets0), io:format("~w~n", [Pet]),

Pet = ets:lookup_element(Pets, bill, 2), ets:delete(Pets, bill), io:format("~w~n", [Pet]),

{value, Pet} = gb_trees:lookup(bill, Pets0), Pets1 = gb_trees:delete(bill, Pets0), io:format("~w~n", [Pet]),

fantom

pet := map.remove("bill")
echo ("pet=$pet")

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')

haskell

import qualified Data.Map as M

main = do
let pets = M.fromList [("joe", "cat"), ("mary", "turtle"), ("bill", "canary")]
pets2 = M.delete "bill" pets
print $ maybe "" id (M.lookup "bill" pets)
print pets2

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')

ruby

puts map.delete :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;

erlang

% Imperative Solution
Histogram = histogram(List),

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

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

fantom

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

fsharp

let histogram = (List.foldLeft (fun (acc : Map<char, int>) (e : char) -> if (Map.mem e acc) then (Map.add e ((Map.find e acc) + 1) acc) ; else (Map.add e 1 acc)) (Map.empty) list)

let histogram list =
let rec histogram' list' dict' =
match list' with
| [] -> dict'
| x :: xs ->
match Map.tryFind x dict' with
| Some(Value) -> histogram' xs (Map.add x (Value + 1) dict')
| None -> histogram' xs (Map.add x 1 dict')
histogram' list Map.empty

// ------

let histogram' = histogram list

let histogram = (List.foldLeft (fun (acc : Generic.Dictionary<char, int>) (e : char) -> (if acc.ContainsKey(e) then acc.[e] <- acc.[e] + 1 ; else acc.Add(e, 1)) ; acc) (new Generic.Dictionary<char, int>()) list)

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

groovy

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

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

haskell

import Data.List
import qualified Data.Map as Map

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

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

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

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

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

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)

ruby

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

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

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

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

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

scala

list foreach { (x) => histogram += x -> (histogram.getOrElse(x, 0) + 1) }

val data = List("a", "b", "a", "c", "b", "b")
val keys = data removeDuplicates
val hist = Map.empty[String, Int] ++ keys.map{ k => (k, (data count (_==k)))}
assert(hist == Map("a"->2, "b"->3, "c"->1))

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

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

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

Categorise a list

Given the list [one, two, three, four, five] produce a map {3:[one, two], 4:[four, five], 5:[three]} which sorts elements into map entries based on their length

clojure

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

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

cpp

for each(String^ entry in input)
{
key = entry->Length;
if (!hash->ContainsKey(key)) hash[key] = gcnew ArrayList;
safe_cast<ArrayList^>(hash[key])->Add(entry);
}

erlang

% Imperative Solution
CatList = categorise(List),

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

fantom

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

fsharp

let catmap = (List.foldLeft (fun (acc : Map<int, List<string> >) (e : string) -> if (Map.mem e.Length acc) then (Map.add e.Length ((Map.find e.Length acc) @ [e]) acc) ; else (Map.add e.Length [e] acc)) (Map.empty) list)

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

groovy

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

haskell

import qualified Data.Map as Map

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

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

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

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

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

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)

ruby

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

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

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

scala

list foreach { (x) => map += x.length -> (x :: map.getOrElse(x.length, Nil)) }

list foreach { (x) => map += x.length -> (map.getOrElse(x.length, Nil) ::: List(x)) }

List("one", "two", "three", "four", "five") groupBy (_ size)

Structure

Conditionals

Perform an action if a condition is true (IF .. THEN)

Given a variable name, if the value is "Bob", display the string "Hello, Bob!". Perform no action if the name is not equal.

clojure

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

cpp

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

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

erlang

if (Name == "Bob") -> io:format("Hello, ~s!~n", [Name]) ; true -> false end.

case Name of "Bob" -> io:format("Hello, ~s!~n", [Name]) ; _ -> false end.

Name == "Bob" andalso (begin io:format("Hello, ~s!~n", [Name]), true end).

fantom

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

fsharp

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

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

groovy

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

haskell

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

ocaml

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

python

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

ruby

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

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

scala

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

val name = "Bob"

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

Perform different actions depending on a boolean condition (IF .. THEN .. ELSE)

Given a variable age, if the value is greater than 42 display "You are old", otherwise display "You are young"

clojure

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

cpp

if (age > 42) Console::WriteLine("You are old");
else Console::WriteLine("You are young");

Console::WriteLine("You are {0}", (age > 42 ? "old" : "young"));

std::printf("You are %s\n", (age > 42 ? "old" : "young"));

erlang

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

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

case Age > 42 of true -> io:format("You are old~n") ; false -> io:format("You are young~n") end.

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

Message = case Age of _ when Age > 42 -> "old" ; _ -> "young" end, io:format("You are ~s~n", [Message]).

Age > 42 andalso (begin io:format("You are old~n"), true end) orelse (begin io:format("You are young~n"), true end).

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

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

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

fantom

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

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

fsharp

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

let message = if age > 42 then "old" else "young"
printfn "You are %s" message

groovy

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

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

haskell

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

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'

ruby

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

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

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

scala

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

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

Replacing a conditional with many branches with a switch/case statement

Many languages support more compact forms of branching than just if ... then ... else such as switch or case or match. Use such a form to add an appropriate placing suffix to the numbers 1..40, e.g. 1st, 2nd, 3rd, 4th, ..., 11th, 12th, ... 39th, 40th

clojure

(def n 112)

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

cpp

#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int num,i,x;
cout<<"Enter the range:";
cin>>num;
for(i=1;i<=num;i++)
{
x=i%10;
switch(i)
{
case 11:
case 12:
case 13:cout<<i<<"th ";
continue;
}
switch(x)
{
case 1: cout<<i<<"st ";break;
case 2: cout<<i<<"nd ";break;
case 3: cout<<i<<"rd ";break;
default: cout<<i<<"th ";
}
}
getch();
}

erlang

Suffix = case Num of
N when N > 10, N < 20 -> "th";
N when N rem 10 =:= 1 -> "st";
N when N rem 10 =:= 2 -> "nd";
N when N rem 10 =:= 3 -> "rd";
_ -> "th"
end,
io_lib:format("~w~s", [Num, Suffix])

fantom

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

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

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

fsharp

let suffix = function
| n when n > 10 && n < 20 -> "th"
| n when n % 10 = 1 -> "st"
| n when n % 10 = 2 -> "nd"
| n when n % 10 = 3 -> "rd"
| _ -> "th"

seq { 1 .. 40 }
|> Seq.iter (fun n -> printfn "%i%s" n (suffix n))

groovy

def suffix(n) {
switch(n) {
case { n % 100 in 4..20 } : return 'th'
case { n % 10 == 1 } : return 'st'
case { n % 10 == 2 } : return 'nd'
case { n % 10 == 3 } : return 'rd'
default : return 'th'
}
}
(1..40).each { n ->
println "$n${suffix(n)}"
}

haskell

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

result = map suffixed [1..40]

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)]

ruby

def suffixed(number)
last_digit = number.to_s[-1..-1].to_i
suffix = case last_digit
when 1 then 'st'
when 2 then 'nd'
when 3 then 'rd'
else 'th'
end
suffix = 'th' if (11..13).include?(number)
"#{number}#{suffix}"
end

(1..40).each {|n| puts suffixed(n) }

scala

object FourToTwenties {
def unapply (n: Int) = (4 to 20).contains(n % 100)
}

def suffix (n: Int) = {
n match {
case FourToTwenties() => "th"
case n if n % 10 == 1 => "st"
case n if n % 10 == 2 => "nd"
case n if n % 10 == 3 => "rd"
case _ => "th"
}
}

for (n <- 1 to 40) {
println(n.toString + suffix(n))
}

Loops

Perform an action multiple times based on a boolean condition, checked before the first action (WHILE .. DO)

Starting with a variable x=1, Print the sequence "1,2,4,8,16,32,64,128," by doubling x and checking that x is less than 150.

clojure

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

cpp

int x = 1;

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

for (int x = 1; x < 150; x *= 2) { std::cout << x << ","; }
std::cout << std::endl;

erlang

X = 1, print_while_X_less_150(X).

Pred = fun (X) -> X < 150 end,
Action = fun (X) -> io:format("~B,", [X]), X * 2 end,
X = 1,

while_do(Pred, Action, X).

fantom

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

fsharp

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

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

groovy

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

haskell

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

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

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

ruby

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

scala

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

Perform an action multiple times based on a boolean condition, checked after the first action (DO .. WHILE)

Simulate rolling a die until you get a six. Produce random numbers, printing them until a six is rolled. An example output might be "4,2,1,2,6"

clojure

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

cpp

Random^ rnd = gcnew Random;

int dice = rnd->Next(1, 7); Console::Write("{0}", dice);
do { Console::Write(",{0}", (dice = rnd->Next(1, 7))); } while (dice != 6);
Console::WriteLine();

erlang

Pred = fun (DiceRoll) -> DiceRoll =/= 6 end,
Action = fun (DiceRoll) -> io:format("~B,", [DiceRoll]), dice_roll() end,

do_while(Pred, Action, dice_roll()).

-module(dice).
-export([start/0]).

start() ->
roll(dice_roll()).

roll(6) ->
io:format("6~n", []);
roll(N) ->
io:format("~B,", [N]),
roll(dice_roll()).

dice_roll() -> random:uniform(6).

fantom

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

fsharp

open System
let rand = Random()

Seq.initInfinite (fun _ -> rand.Next(1, 7))
|> Seq.takeWhile (fun x -> x < 6)
|> fun items -> String.Join(",", items)
|> function s when s = "" -> printfn "6" | s -> printfn "%s,6" s

groovy

// Groovy has no do..while; use a normal while
int dice = 0
while (dice != 6) {
dice = Math.random() * 6 + 1
print dice
if (dice != 6) print ','
}

haskell

import System.Random

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

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()))

ruby

# Ruby has no DO..WHILE construct. Need to write it as a WHILE
rnd = 0
while (rnd != 6)
rnd = rand(6)+1
print rnd
print "," if (rnd!=6)
end

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

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

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

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

scala

val dice = new GenRandInt(1, 6) ; var rnd = 0 ; var fmt = ""
do { rnd = dice.next ; fmt = if (rnd != 6) "%d," else "%d" ; printf(fmt, rnd) } while (rnd != 6)

Perform an action a fixed number of times (FOR)

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

clojure

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

cpp

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

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

dotimes(5, hello);

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

erlang

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

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

fantom

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

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

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

fsharp

for i = 1 to 5 do printf "Hello" done

dotimes 5 (fun () -> printf "Hello")

// Repetition via ranging over a List type(index ignored)
for _ in list do printf "Hello" done

// Repetition via ranging over a Sequence type(index ignored)
for _ in sequence do printf "Hello" done

// Repetition via ranging over an Array type(index ignored)
for _ in array do printf "Hello" done

groovy

println "Hello" * 5

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

haskell

import Control.Monad

hi5 = replicateM_ 5 $ putStr "Hello"

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"

ruby

puts "Hello"*5

5.times { print "Hello" }

scala

// Using overloaded '*' operator (String-specific)
print("Hello" * 5)

List.range(0, 5) foreach { (_) => print("Hello") }

for (_ <- List.range(0, 5)) print("Hello")

// Lazy version
for (_ <- Stream.range(0, 5)) print("Hello")

dotimes(5, _ => print("Hello"))

(0 until 5) foreach { (_) => print("Hello") }

5 times { print("Hello") }

Perform an action a fixed number of times with a counter

Display the string "10 .. 9 .. 8 .. 7 .. 6 .. 5 .. 4 .. 3 .. 2 .. 1 .. Liftoff!"

clojure

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

(println "Liftoff!")

cpp

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

erlang

fromto(10, 1, -1, fun (X) -> io:format("~B .. ", [X]) end), io:format("Liftoff!~n").

lists:foreach(fun (X) -> io:format("~B .. ", [X]) end, lists:seq(10, 1, -1)), io:format("Liftoff!~n").

fantom

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

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

fsharp

for i = 10 downto 1 do printf "%d .. " i done
printfn "Liftoff!"

// Repetition via ranging over a Sequence type
for i in {10 .. -1 .. 1} do printf "%d .. " i done ; printfn "Liftoff!"

groovy

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

haskell

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

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!"

ruby

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

scala

for (i <- List.range(1, 11).reverse) printf("%d .. ", i) ; println("Liftoff!")

for (i <- List.range(-10, 0)) printf("%d .. ", (-i)) ; println("Liftoff!")

var i = 10 ; while (i > 0) { printf("%d .. ", i) ; i -= 1 } ; println("Liftoff!")

for (i <- -10 to -1) printf("%d .. ", (-i)) ; println("Liftoff!")

Files

Reading

Read the contents of a file into a string

clojure

(slurp "/tmp/foobar")

cpp

IO::FileStream^ file; String^ buffer;

try
{
file = gcnew IO::FileStream("test.txt", IO::FileMode::Open);
buffer = gcnew String((gcnew IO::BinaryReader(file))->ReadChars(file->Length));
}

IO::StreamReader^ stream; String^ buffer;

try
{
stream = gcnew IO::StreamReader("test.txt");
buffer = stream->ReadToEnd();
}

String^ buffer = IO::File::ReadAllText("test.txt");

erlang

Text = readfile("Solution607.erl"),

Text = readfile("Solution608.erl"),

fantom

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

fsharp

let file = new FileStream("test.txt", FileMode.Open)
let buffer = new String((new BinaryReader(file)).ReadChars(Convert.ToInt32(file.Length)))

let stream = new StreamReader("test.txt")
let buffer = stream.ReadToEnd()

let buffer = File.ReadAllText("test.txt")

groovy

contents = file.text

haskell

readFile "c:/tmp/myFile.txt"

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()

ruby

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

scala

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

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

Process a file one line at a time

Open the source file to your solution and print each line in the file, prefixed by the line number, like:
1> First line of file
2> Second line of file
3> Third line of file

clojure

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

cpp

IO::StreamReader^ stream; String^ ln; int i = 0;

try
{
stream = gcnew IO::StreamReader("test.txt");
while ((ln = stream->ReadLine())) Console::WriteLine("{0}> {1}", ++i, ln);
}

int i = 0;
for each(String^ line in IO::File::ReadAllLines("test.txt")) Console::WriteLine("{0}> {1}", ++i, line);

erlang

Reader = fun (IODevice) -> io:get_line(IODevice, "") end,
Worker = fun (Line, N) -> io:format("~B> ~s", [N, Line]), N + 1 end,

while_not_eof("Solution609.erl", Reader, Worker, 1).

Reader = fun (Filename) -> {ok, Contents} = file:read_file(Filename), Contents end,
Transformer = fun (Line, N) -> string:concat(string:concat(integer_to_list(N), "> "), Line) end,
Printer = fun (Line) -> io:format("~s~n", [Line]) end,

Lines = string:tokens(binary_to_list(Reader("Solution610.erl")), "\n"),
NewLines = lists:zipwith(Transformer, Lines, lists:seq(1, length(Lines))),
lists:foreach(Printer, NewLines).

fantom

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

fsharp

let stream = new StreamReader("test.txt")
let mutable i = 1
let mutable line = stream.ReadLine()
while (line <> null) do printfn "%d> %s" i line ; line <- stream.ReadLine() ; i <- i + 1 done
stream.Close()

let proc_a_line (filename : string) proc =
let stream = new StreamReader(filename)
let rec proc_a_line' count line =
match line with
| null -> stream.Close()
| _ -> proc count line ; proc_a_line' (count + 1) (stream.ReadLine())
proc_a_line' 1 (stream.ReadLine())

// ------

let _ = proc_a_line "test.txt" (fun i line -> printfn "%d> %s" i line)

let reader(filename : string) = seq {
use sr = new StreamReader(filename)
while not sr.EndOfStream do
let line = sr.ReadLine()
yield line
done
}

// ------

reader("test.txt") |> Seq.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

File.ReadAllLines("test.txt") |> Array.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

// Unlike ReadAllLines, ReadLines (new in .NET 4) only reads the file
// one line at a time, rather than reading the entire file into an array first.

open System.IO
File.ReadLines("test.txt") |> Seq.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

groovy

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

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

haskell

import Data.List

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

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

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

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

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

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())

ruby

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

scala

val source = Source.fromFile(new File("Solution468.scala")).getLines
var n = 1 ; while (source.hasNext) { printf("%d> %s", n, source.next) ; n += 1 }

val source = Source.fromFile(new File("Solution469.scala")).getLines
for ((line, n) <- source zipWithIndex) { printf("%d> %s", (n + 1), line) }

Writing

Write a string to a file

clojure

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

cpp

IO::StreamWriter^ stream;

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

erlang

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

fantom

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

fsharp

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

groovy

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

file.text = 'some text'

haskell

writeFile "filename" "stringe"

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!')

ruby

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

scala

FileUtils.writeStringToFile(new File("test.txt"), "This line overwites file contents!")

val fw = new FileWriter("test.txt") ; fw.write("This line overwites file contents!") ; fw.close()

Append to a file

clojure

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

cpp

IO::StreamWriter^ stream;

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

erlang

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

fantom

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

fsharp

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

groovy

file << 'some text'

haskell

appendfile "filename" "string"

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')

ruby

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

scala

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

Directories

Process each file in a directory

clojure

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

cpp

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

erlang

% File basenames only - many tasks require absolute paths to work
lists:foreach(fun (FileOrDirPath) -> Worker(FileOrDirPath) end, file:list_dir(Directory)).

% Absolute paths provided - will accomodate most tasks
lists:foreach(fun (FileOrDirPath) -> Worker(FileOrDirPath) end, list_dir_path(Directory)).

fantom

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

fsharp

let dirname = "c:\\"

let processFile filename = printfn "%s" filename
for filename in Directory.GetFiles(dirname) do processFile filename done

let dirname = "c:\\"

Directory.GetFiles(dirname) |> Array.iter (fun filename -> printfn "%s" filename)

groovy

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

haskell

import System.Directory
import Control.Monad

process filename = putStrLn filename

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

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))

ruby

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

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:\\");
}

erlang

filelib:fold_files(Directory, ".*", true, fun (FileOrDirPath, Acc) -> Worker(FileOrDirPath), Acc end, []).

process_dir(Directory, Worker).

fantom

File(`./`).walk { process(it) }

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) }

haskell

import System.Directory (doesFileExist, getDirectoryContents)
import System.FilePath ((</>))

process :: FilePath -> IO ()
process filename = putStrLn filename

mapDir :: (FilePath -> IO ()) -> FilePath -> IO ()
mapDir proc fp = do
isFile <- doesFileExist fp -- is a file of fp
if isFile then proc fp -- process the file
else getDirectoryContents fp >>=
mapM_ (mapDir proc . (fp </>)) . filter (`notElem` [".", ".."])

main = mapDir process "."

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)

ruby

def procdir(dirname)
Dir.foreach(dirname) do |dir|
dirpath = dirname + '/' + dir
if File.directory?(dirpath) then
if dir != '.' && dir != '..' then
puts "DIRECTORY: #{dirpath}" ; procdir(dirpath)
end
else
puts "FILE: #{dirpath}"
end
end
end

# ------

procdir('/tmp')

scala

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

Dates

Creation

Display the current date and time

Create a Date object representing the current date and time. Print it out.
If you can also do this without creating a Date object you can show that too.

clojure

(import 'java.util.Date)

(println (str (Date.)))

cpp

QDate now = QDate::currentData();
qDebug() << now.toString();

time_t date = time(0);
cout << ctime(&date);

erlang

io:format("~p~n", [calendar:local_time()])

fantom

echo(DateTime.now)

fsharp

printfn "%A" System.DateTime.Now

groovy

println new Date()

haskell

import System.Time

main = do ct <- getClockTime
print ct

import Data.Time

main = do zt <- getZonedTime
print zt

ocaml

Unix.localtime (Unix.gettimeofday ())

python

from datetime import datetime
print datetime.utcnow()

ruby

puts DateTime.now

scala

println(new java.util.Date)

OOP

Basics

Define a class

Declare a class named Greeter that takes a string on creation and greets using this string if you call the "greet" method.

clojure

(defprotocol IGreeter
(greet [this]))

(deftype Greeter [whom]
IGreeter
(greet [this]
(println (str "Hello, " whom))))

(greet (Greeter. "world"))

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

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

(greet (greeter "world"))

cpp

class Greeter
{
public:
Greeter(const std::string& whom);
void greet() const;

private:
std::string whom;
};

int main()
{
Greeter* gp = new Greeter("world");
gp->greet();
delete gp;
}

Greeter::Greeter(const std::string& whom) : whom(whom) {}

void Greeter::greet() const
{
std::cout << "Hello, " << whom << std::endl;
}

public ref class Greeter
{
public:
Greeter(String^ whom);
void greet();

private:
initonly String^ whom;
};

int main()
{
(gcnew Greeter(L"world"))->greet();
}

Greeter::Greeter(String^ whom) : whom(whom) {}

void Greeter::greet()
{
Console::WriteLine(L"Hello, {0}", whom);
}

erlang

Greeter = make_greeter("world!"),
Greeter(greet).

fantom

class Greeter
{
private Str whom
new make(Str whom) { this.whom = whom }
Void greet() { echo("Hello, $whom") }
}

Greeter("world").greet

fsharp

type Greeter(whom' : string) =
member this.greet() = printfn "Hello, %s!" whom'

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

type Greeter(whom' : string) =
let whom : string = whom'
member this.greet() = printfn "Hello, %s!" whom

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

type Greeter =
class
val whom : string
new(whom') = { whom = whom' }
member this.greet() = printfn "Hello, %s!" this.whom
end

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

groovy

// version using named parameters
class Greeter {
def whom
def greet() { println "Hello, $whom" }
}
new Greeter(whom:'world').greet()

// version using traditional constructor
class Greeter {
private whom
Greeter(whom) { this.whom = whom }
def greet() { println "Hello, $whom" }
}
new Greeter('world').greet()

haskell

data Greeter = Greeter String

class Greets a where
greet :: a -> IO ()

instance Greets Greeter where
greet (Greeter s) = print s

main = greet (Greeter "Hello")

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()

ruby

class Greeter
def initialize(whom) @whom = whom end
def greet() puts "Hello, #{@whom}!" end
end

(Greeter.new("world")).greet()

scala

class Greeter(whom : String) { def greet() = { printf("Hello %s\n", whom) } }

(new Greeter("world!")).greet()

XML

Parsing

Process an XML document

Given the XML Document:

<shopping>
<item name="bread" quantity="3" price="2.50"/>
<item name="milk" quantity="2" price="3.50"/>
</shopping>

Print out the total cost of the items, e.g. $14.50

clojure

(println (format "Total cost of items are $%#.2f"
(->> (xml-seq (parse *xml-input-stream*))
(filter #(= :item (:tag %))) ; Remove all but the item tags
(map :attrs) ; Keep the attributes
(map (fn [e] (str "(* " (:quantity e) " " (:price e) ")"))) ; Get the total price as a sexp
(map read-string) ; "(* quantity price)" -> (* quantity price)
(map eval) ; (* quantity price) -> quantity*price
(apply +)))) ; Sum all elements

cpp

char input[] =
"<shopping>"
" <item name=\"bread\" quantity=\"3\" price=\"2.50\"/>"
" <item name=\"milk\" quantity=\"2\" price=\"3.50\"/>"
"</shopping>";

xml_document<> doc;
doc.parse<0>(input);
xml_node<> *shopping = doc.first_node();

float total_price = 0;
for (xml_node<> *item = shopping->first_node(); item != NULL; item = item->next_sibling())
{
float item_sum = 0;
float val;

if (string(item->name()) != "item")
continue;

for (xml_attribute<> *attr = item->first_attribute(); attr != NULL; attr = attr->next_attribute())
{
string name(attr->name());
if (name == "quantity" || name == "price")
{
stringstream v(attr->value());
v >> val;
if (item_sum)
item_sum *= val;
else
item_sum = val;
}
}
total_price += item_sum;
}

cout.setf(ios::fixed, ios::floatfield);
cout << "Total price is $" << setprecision(2) << total_price << endl;

erlang

-include_lib("xmerl/include/xmerl.hrl").
-export([get_total/1]).

get_total(ShoppingList) ->
{XmlElt, _} = xmerl_scan:string(ShoppingList),
Items = xmerl_xpath:string("/shopping/item", XmlElt),
Total = lists:foldl(fun(Item, Tot) ->
[#xmlAttribute{value = PriceString}] = xmerl_xpath:string("/item/@price", Item),
{Price, _} = string:to_float(PriceString),
[#xmlAttribute{value = QuantityString}] = xmerl_xpath:string("/item/@quantity", Item),
{Quantity, _} = string:to_integer(QuantityString),
Tot + Price*Quantity
end,
0, Items),
io:format("$~.2f~n", [Total]).

fantom

sum := 0.0
root := XParser(File(`shop.xml`).in).parseDoc.root
if (root.name == "shopping")
{
root.elems.each
{
if (it.name == "item")
{
quantity := Int.fromStr(it.get("quantity"))
price := Decimal.fromStr(it.get("price"))
sum += quantity * price;
}
}
}
echo("\$$sum")

fsharp

#r @"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\v3.5\System.Xml.Linq.dll"

open System
open System.Xml.Linq
//XElement Helper
let xname sname = XName.Get sname

let xmlsnippet =
let snippet = new XElement(xname "shopping")
//create bread
let bread = new XElement(xname "item")
bread.SetAttributeValue(xname "name","bread")
bread.SetAttributeValue(xname "quantity",3)
bread.SetAttributeValue(xname "price",2.50)
//add bread to snippet
snippet.Add(bread)
//create milk
let milk = new XElement(xname "item")
milk.SetAttributeValue(xname "name","milk")
milk.SetAttributeValue(xname "quantity",2)
milk.SetAttributeValue(xname "price",3.50)
//add milk to snippet
snippet.Add(milk)
snippet

let totalprice (xe: XElement) =
xe.Descendants(xname "item")
|> Seq.map(fun i -> Double.Parse(i.Attribute(xname "price").Value))
|> Seq.fold(fun acc x -> acc + x) 0.0

let xname sname = XName.Get sname
let xattr (elem: XElement) sname = elem.Attribute(xname sname).Value
let xml = XDocument.Load("xml.txt")

let shoppingCost =
xml.Descendants(xname "item")
|> Seq.map (fun i -> Double.Parse(xattr i "quantity"), Double.Parse(xattr i "price"))
|> Seq.sumBy (fun (quantity, price) -> quantity * price)

// Alternative solution that uses XML Navigation, and XPath expressions to ensure that
// the items have the required attributes
let xname sname = XName.Get sname
let xattr (elem: XElement) sname = elem.Attribute(xname sname).Value

let navigator = XPathDocument("xml.txt").CreateNavigator()
let path = XPathExpression.Compile("/shopping/item[@price][@quantity]")
let names = XmlNamespaceManager(navigator.NameTable)
path.SetContext(names)
let shoppingCost =
match path.ReturnType with
| XPathResultType.NodeSet ->
navigator.Select(path)
|> Seq.cast
|> Seq.map (fun (i: XPathNavigator) ->
if i.IsNode then
let elem = XElement.Parse(i.OuterXml)
Double.Parse(xattr elem "quantity"), Double.Parse(xattr elem "price")
else
failwith "Error in expression, expecting to see a node"
)
|> Seq.sumBy (fun (quantity, price) -> quantity * price)
| _ -> failwith "Error in expression, expecting to see a node set"

groovy

printf '$%.2f\n', new XmlSlurper().parseText(xml).item.collect{
it.@quantity.toInteger() * it.@price.toFloat()
}.sum()

haskell

File Edit Options Buffers Tools Haskell Help
import Text.ParserCombinators.Parsec
import Control.Monad
import System ( getArgs )

data Item = Item { name :: String,
quantity :: Int,
price :: Int }
deriving Show

type Basket = [Item]

item :: Parser Item
item = do string "<item name=\""
name <- manyTill letter (char '\"')
string " quantity=\""
quantity <- liftM read $ many digit
string "\" price=\""
dollars <- liftM read $ many digit
cents <- option 0 (char '.' >> (liftM read $ many digit))
string "\"/>"
return $ Item name quantity (100 * dollars + cents)

basket :: Parser Basket
basket = do string "<shopping>"
items <- manyTill item (try $ string "</shopping>")
return items

parseBasket :: String -> Basket
parseBasket input = case parse basket "Shopping Basket" input of
Left _ -> []
Right val -> val

main = do args <- getArgs
putStrLn $ show . (/100) . fromIntegral . sum . map (\(Item _ q p) -> q * p) . parseBasket $ head args

import Text.XML.HXT.Core
import Text.Printf

main :: IO ()
main = do
prices <- runX (process "basket.xml")
printf "$%.2f\n" $ sum prices

process :: FilePath -> IOSArrow XmlTree Double
process filename =
readDocument [withValidate no] filename >>>
getChildren >>>
isElem >>> hasName "shopping" >>>
getChildren >>>
isElem >>> hasName "item" >>>
getQuantity &&& getPrice >>>
arr (uncurry (*))

getQuantity :: IOSArrow XmlTree Double
getQuantity =
getAttrl >>> hasName "quantity" >>> getChildren >>>
getText >>> arr read

getPrice :: IOSArrow XmlTree Double
getPrice =
getAttrl >>> hasName "price" >>> getChildren >>>
getText >>> arr read

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

ruby

#!/usr/bin/env ruby

# needed to parse xml
require 'rexml/document'

# grab the file
file = File.new('shop.xml')

# load it as an xml document
doc = REXML::Document.new(file)

# initialize the total to 0 as a float
total = 0.0

# cycle through the items
doc.elements.each('shopping/item') do |item|

# add the price to the total
total += item.attributes['price'].to_f
end

# round the total to the nearest 0.01
total = (total*100.0).round/100.0

# pad the output with the proper number of trailing 0's
printf "$%.2f\n", total

scala

val data = <shopping>
<item name="bread" quantity="3" price="2.50"/>
<item name="milk" quantity="2" price="3.50"/>
</shopping>

val res = for (
item <- data \ "item" ;
price = (item \ "@price").text.toDouble ;
qty = (item \ "@quantity").text.toInt)
yield (price * qty)

printf("$%.2f\n", res.sum)

Algorithms

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;

erlang

find_all_pythagorean_triangles(L) ->
lists:sort(fun({_, _, H1}, {_, _, H2}) -> H1 =< H2 end,
[ { X, Y, Z } ||
X <- lists:seq(1,L),
Y <- lists:seq(1,L),
Z <- lists:seq(1,2*L),
X*X + Y*Y =:= Z*Z,
Y > X,
Z > Y
]).

main(_) ->
List = find_all_pythagorean_triangles(20).

fantom

triangles := [,]
(1..20).each |Int a|
{
(a..20).each |Int b|
{
c := (a.pow(2) + b.pow(2)).toFloat.sqrt
if (c % c.toInt == 0.0f && !triangles.contains([b,a,c]))
triangles.add([a,b,c.toInt])
}
}
triangles.sort |Int[] x, Int[] y -> Int| { x[2]-y[2] }
echo(triangles)

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')

haskell

import Data.List
import Control.Monad

pythTriangles :: [(Int,Int,Int)]
pythTriangles = do
a <- [1..20]
b <- [a+1..20]
c <- [1..2*b]
guard (a*a + b*b == c*c)
return (a,b,c)

cmpThird (_,_,a) (_,_,b)
| a < b = LT
| a == b = EQ
| otherwise = GT

main = mapM_ print (sortBy cmpThird pythTriangles)

import Data.Function
import Data.List

pythTriangles =
[(a,b,c) | a <- [1..20], b <- [a+1..20], c <- [1..2*b], a*a + b*b == c*c]

main = mapM_ print $ sortBy (compare `on` third) pythTriangles where
third (_,_,x) = x

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))]))

ruby

results=[]

1.upto(20) do |a|
1.upto(20) do |b|
c=Math.sqrt(a**2+b**2)
results<<[a, b, c.to_i] if c.to_i==c && !results.index([b, a, c.to_i])
end
end

results=results.sort_by{|r| r[2]}

puts results

def find_pythag( max=20 )
r = []
1.upto max do |n|
n.upto max do |m|
h = Math.sqrt( n**2 + m**2)
r << [n,m,h.to_i] if (h.round - h).zero?
end
end
r.sort_by { |a| a[2] }
end

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;
}

erlang

-module(gcd).
-export([gcd/2]).

gcd(A, 0) -> A;
gcd(A, B) -> gcd(B, A rem B).

fantom

gcd := |Int a, Int b -> Int| {
pair := [a, b].sort
while (pair.first != 0)
pair.set(1, pair.last % pair.first).swap(0, 1)
return pair.last
}
echo(gcd(12, 8)) // a>b, result == 4
echo(gcd(1029, 1071)) // a<b, result == 21

fsharp

let rec gcd x y =
if y = 0 then x
else gcd y (x % y)

groovy

static def gcd(int i, int j) {
if (Math.min(i,j)==0) return Math.max(i,j)
else return gcd(Math.min(i,j),Math.abs(i-j))
}

haskell

8 `gcd` 12

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)

ruby

135.gcd(30)
# => 15

scala

def gcd(x: Int, y: Int): Int =
if (b == 0) x
else gcd(b, x % y)

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;
}
}

erlang

-module(spam).
-export([spam/1]).

spam(N) when N<5 ->
spawn(fun() -> io:format("Hello World from thread ~p~n",[N]) end),
spam(N+1);
spam(_) -> void.

fantom

pool := ActorPool()
["one", "two", "three", "four"].each
{
a := Actor(pool) |Str name| { echo("Thread $name says Hello World!") }
a.send(it)
}

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!"
}
}

haskell

mapM_ (\x -> forkIO (putStrLn ("Thread " ++ x ++ " says Hello World!"))) ["one", "two", "three", "four"]

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()

ruby

%w[one two three four].each do |number|
Thread.new(number) { |number|
puts "Thread #{number} says Hello World!"
}.join
end

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")))