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Solved Problems

Strings

Printing

Output a string to the console

Write the string "Hello World!" to STDOUT

ruby

puts "Hello World!"

$stdout<<"Hello World!"

csharp

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

clojure

(println "Hello World!")

fsharp

printfn "Hello World!"

cpp

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

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

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

fmt.Printf("Hello, world\n")

fmt.Println("Hello, World!")

Declaration

Define a string containing special characters

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

ruby

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

csharp

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

clojure

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

fsharp

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

cpp

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

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

s := "\\#{'}${\"}/"

s := `"\#{'}${"}/"`

Define a multiline string

Define the string:

"This

Is

A

Multiline

String"

ruby

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

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

csharp

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

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

clojure

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

fsharp

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

let multiline = "This
Is
A
Multiline
String"

cpp

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

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

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

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

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

var s = `This
Is
A
Multiline
String`

Define a string containing variables and expressions

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

ruby

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

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

csharp

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

clojure

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

fsharp

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

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;

a, b := 3, 4
fmt.Printf("%d+%d=%d\n", a, b, a + b)

a, b := 3, 4
fmt.Println(a, "+", b, "=", a+b)

Manipulation

Reverse the characters in a string

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

ruby

puts "reverse me".reverse

csharp

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

clojure

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

(apply str (reverse "reverse me"))

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) []

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());

package main;
import "utf8";
import "fmt";

func reverse(s string) string {
o := make([]int, utf8.RuneCountInString(s))
i := len(o)
for _, c := range s {
i--
o[i] = c
}
return string(o)
}

func main() {
fmt.Print(reverse("reverse me"));
}

func Reverse(s string) string {
runes := []rune(s)
for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
runes[i], runes[j] = runes[j], runes[i]
}
return string(runes)
}

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"

ruby

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

csharp

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

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!"))))

fsharp

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

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();

words := strings.Split("This is the end, my only friend!", " ")
nr := len(words)
reversed := make([]string, nr)
for i, word := range words {
reversed[nr - i - 1] = word
}
s := strings.Join(reversed, " ")
fmt.Println(s)

func reverse(list []string) ([]string) {
if len(list) == 1 {
return list
}

return append(reverse(list[1:]), list[0])
}

func main() {
words := strings.Split("This is the end, my only friend!", " ")
s := strings.Join(reverse(words), " ")
fmt.Println(s)
}

Text wrapping

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

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

ruby

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

csharp

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

public class TextWrapper {

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

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

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

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

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

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

return result.ToString();
}

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

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

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

clojure

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

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

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);
}

import "fmt"
import "strings"

const WIDTH = 72

func main() {
s := "The quick brown fox jumps over the lazy dog."

words := strings.Split(s, " ")
tmp := words

for i, pos := 0, 0; i < 10; i++ {
for len(words) > 0 {
if pos == 0 {
fmt.Printf("> ")
}

if pos + len(words[0]) > WIDTH {
fmt.Printf("\n")
pos = 0
} else {
fmt.Printf("%s ", words[0])
pos += len(words[0]) + 1
words = words[1:]
}
}
words = tmp
}

fmt.Printf("\n")
}

Remove leading and trailing whitespace from a string

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

ruby

puts " hello ".strip

" hello ".strip!

csharp

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

clojure

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

(clojure.string/trim " hello ")

(.trim " hello ")

fsharp

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

let trimmed = " hello ".Trim()

cpp

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

s := strings.TrimSpace(" hello ")

Case

Make a string uppercase

Transform "Space Monkey" into "SPACE MONKEY"

ruby

uppper = text.upcase

csharp

string output = "Space Monkey"

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

clojure

(.toUpperCase "Space Monkey")

fsharp

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

printfn "%s" (String.uppercase "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);

strings.ToUpper("Space Monkey")

Make a string lowercase

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

ruby

"Caps ARE overRated".downcase

csharp

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

clojure

(.toLowerCase "Caps ARE overRated")

fsharp

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

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

cpp

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

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

strings.ToLower("Caps ARE overRated")

Capitalise the first letter of each word

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

ruby

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

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

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

csharp

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

clojure

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

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"

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();

strings.Title(strings.ToLower("man OF stEEL"))

Numbers

Mathematical

Find the distance between two points

ruby

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

csharp

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

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])

fsharp

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

cpp

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

import "fmt"
import "math"

type Point struct {
x, y float64
}

func (p Point) distance(other Point) (float64) {
dx := p.x - other.x
dy := p.y - other.y
return math.Sqrt(dx * dx + dy * dy)
}

func main() {
origin := Point{ 0, 0 }
point := Point{ 1, 1 }

fmt.Println(point.distance(origin))
}

Output

Zero pad a number

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

ruby

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

"%08d" % 42

csharp

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

clojure

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

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

(format "%08d" 42)

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)

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;

fmt.Printf("%08d", 42)

Right Space pad a number

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

ruby

1024.to_s.ljust(6)

csharp

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

clojure

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

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)

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;

fmt.Printf("%-6d", 1024)

Format a decimal number

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

ruby

(7.0/8.0*100).round/100.0

(7.0/8.0).round(2)

csharp

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

clojure

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

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

fsharp

printfn "%3.2f" (0.7 / 0.8)

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

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;

fmt.Printf("%.2f", 7.0 / 8.0)

Left Space pad a number

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

ruby

73.to_s.rjust(10)

csharp

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

clojure

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

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)

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;

fmt.Printf("%10d", 73)

Random

Generate a random integer in a given range

Produce a random integer between 100 and 200 inclusive

ruby

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

csharp

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

clojure

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

fsharp

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

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();

rand.Intn(100) + 100

Generate a repeatable random number sequence

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

ruby

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

csharp

using System;

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

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

r = new Random(12);

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

clojure

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

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 ""

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);

rand.Seed(0xdeadbeef)
for i := 0; i < 5; i++ {
fmt.Printf("%v ", rand.Int())
}
fmt.Println()

rand.Seed(0xdeadbeef)
for i := 0; i < 5; i++ {
fmt.Printf("%v ", rand.Int())
}
fmt.Println()

Regex

Matching

Check if a string matches a regular expression

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

ruby

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

csharp

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

clojure

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

fsharp

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

result, _ := regexp.MatchString("[A-Z][a-z]+", "Hello")
if result {
fmt.Println("ok")
}

Check if a string matches with groups

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

ruby

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

csharp

using System;
using System.Text.RegularExpressions;

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

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

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

clojure

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

fsharp

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

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;

re, _ := regexp.Compile("one (.*) three")
groups := re.FindStringSubmatch("one two three")
if len(groups) > 0 {
fmt.Println(groups[1])
}

Lists

Declaration

Define an empty list

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

ruby

list = []

list = Array.new

csharp

var list = new List<object>();

clojure

(list)

'()

fsharp

let list = []

let list = List.empty

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

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

cpp

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

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

var l []string;

Define a static list

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

ruby

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

list = %w(One Two Three Four Five)

csharp

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

clojure

(def a '[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))

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";

var l = []string{"One", "Two", "Three", "Four", "Five"}

Output

Join the elements of a list, separated by commas

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

ruby

string = fruit.join(', ')

csharp

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

clojure

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

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()

cpp

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

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

s := strings.Join([]string {"Apple", "Banana", "Carrot"}, ", ")

Access

Fetch an element of a list by index

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

ruby

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

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

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

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

csharp

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

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

clojure

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

fsharp

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

cpp

String^ result = list[2];

fmt.Println(list[2])

Modification

Remove an element from a list by index

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

ruby

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

fruit.delete_at(0)

csharp

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

clojure

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

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)

cpp

fruit->RemoveAt(0);

offset := 0
list = append(list[:offset], list[offset+1:]...)

Maps

Algorithms

Create a histogram map from a list

Given the list [a,b,a,c,b,b], produce a map {a:2, b:3, c:1} which contains the count of each unique item in the list

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}

csharp

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

// This is a "functional" C# approach

// NOTE: In C# "maps" are of type Dictionary<Tkey, TValue>
// so our histogram map is of type Dictionary<object, int>
public class HistogramMap {
public Dictionary<object, int> FromList(List<object> list) {
// The "Aggregate" method works like "inject" in many other languages.
return list.Aggregate(
new Dictionary<object, int>(),
(map, obj) => {
// If this is the first time we've seen this obj, set the count to 0
if (!map.ContainsKey(obj)) map[obj] = 0;

// Increment the count
map[obj]++;

// Return the map for the next iteration.
// NOTE: This does NOT return from our "FromList" method
return map;
}
);
}

public static void Main() {
// Create our Histogram Map from a new list
var map = new HistogramMap().FromList(
new List<object>() { 'a', 'b', 'a', 'c', 'b', 'b' }
);

// This just prints the result
System.Console.WriteLine (
string.Join (", ",
// "Select" works like "map" or "collect" in many other languages
map.Select( kvp =>
string.Format("{0} : {1}", kvp.Key, kvp.Value)
).ToArray()
)
);
}
}

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

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])

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

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;

var maplist = make(map[string]int)
var list = [6]string{"a","b","a","c","b","b"}
for _, v := range list {
maplist[v] += 1
}
fmt.Println(maplist)

Dates

Parsing

Parse a date and time from a string

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

ruby

# With timezone info
puts Time.parse('2008-05-06 13:29')

csharp

DateTime parsedDate = DateTime.Parse("2008-05-06 13:29");
// Ideally, you would catch the potential FormatException or use DateTime.TryParse in production code.

clojure

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

fsharp

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

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

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

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

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

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

cpp

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

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

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

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

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

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

t, err := time.Parse("2006-01-02 15:04", "2008-05-06 13:29")
if err == nil {
fmt.Println(t)
}

Printing

Display information about a date

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

ruby

require 'date'

next_week = Date.today + 8

puts next_week.day # day of month
puts next_week.yday # day of year
puts next_week.strftime('%B') # month name
puts next_week.strftime('%A') # day name

csharp

DateTime date = DateTime.Today.AddDays(8);

Console.WriteLine("Day of month: " + date.Day);
Console.WriteLine("Day of year: " + date.DayOfYear);
Console.WriteLine("Month name: " + date.ToString("MMMM"));
Console.WriteLine("Day name: " + date.ToString("dddd"));

// The two ToString calls will use the current locale.
// To get localised month and day names, see http://msdn.microsoft.com/en-us/library/8tfzyc64.aspx

clojure

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

fsharp

Using F# interactive

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

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

>

cpp

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

t := time.Now().Add(8 * 24 * time.Hour)
fmt.Println(t.Day())
// no day of year
fmt.Println(t.Month())
fmt.Println(t.Weekday())

Creation

Display the current date and time

Create a Date object representing the current date and time. Print it out.
If you can also do this without creating a Date object you can show that too.

ruby

puts DateTime.now

csharp

// Creating a variable first:
DateTime now = DateTime.Now;
Console.WriteLine(now);

// Without creating a variable:
Console.WriteLine(DateTime.Now);

clojure

(import 'java.util.Date)

(println (str (Date.)))

fsharp

printfn "%A" System.DateTime.Now

cpp

QDate now = QDate::currentData();
qDebug() << now.toString();

time_t date = time(0);
cout << ctime(&date);

fmt.Println(time.Now())

OOP

Basics

Define a class

Declare a class named Greeter that takes a string on creation and greets using this string if you call the "greet" method.

ruby

class Greeter
def initialize(whom) @whom = whom end
def greet() puts "Hello, #{@whom}!" end
end

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

csharp

using System;

class Greeter
{
private string name {get;set;}

public void Greet(){
Console.WriteLine("Hello, {0}",name);
}

public Greeter(string name){
this.name = name;
}
}

class Test
{
static void Main()
{
new Greeter("Dante").Greet();
}
}

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"))

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()

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);
}

type Greeter struct {
whom string
}

func (g Greeter) greet() {
fmt.Printf("Hello %s\n", g.whom)
}

func main() {
Greeter{"world"}.greet()
}