Solved Problems

Output a string to the console

Write the string "Hello World!" to STDOUT
python
print "Hello World!"
csharp
System.Console.WriteLine("Hello World!")
java
System.out.println("Hello World!");
System.out.printf("Hello World!\n");
erlang
io:format("Hello, World!~n").
cpp
std::cout << "Hello World" << std::endl;
std::printf("Hello World\n");
Console::WriteLine(L"Hello World");

Define a string containing special characters

Define the literal string "\#{'}${"}/"
python
# yes, Python has way too many forms of string literals :)
print "\\#{'}${\"}/"
print "\\#{'}${"'"'"}/"
print r"""\#{'}${"}/"""
print '\\#{\'}${"}/'
print '\\#{'"'"'}${"}/'
print r'''\#{'}${"}/'''
csharp
string verbatim = @"\#{'}${""""}/";
string cStyle = "\\#{'}${\"\"}/";
java
String special = "\\#{'}${\"}/";
erlang
Special = "\\#{'}\${\"}/",
cpp
std::string special = "\\#{'}${\"}/";
String^ special = L"\\#{'}${\"}/";

Define a multiline string

Define the string:
"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"
)
csharp
string output = "This\nIs\nA\nMultiline\nString";
string output = @"This
Is
A
Multiline
String";
java
String text = "This\nIs\nA\nMultiline\nString";
String text =
"This\n" +
"Is\n" +
"A\n" +
"Multiline\n" +
"String"
erlang
Text = "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";

Define a string containing variables and expressions

Given variables a=3 and b=4 output "3+4=7"
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)
csharp
int a = 3;
int b = 4;
Console.WriteLine("{0}+{1}={2}", a,b,a+b);
java
System.out.println(a + "+" + b + "=" + (a+b));
System.out.printf("%d+%d=%d\n", a, b, a + b);
erlang
A = 3, B = 4,
io:format("~B+~B=~B~n", [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;

Reverse the characters in a string

Given the string "reverse me", produce the string "em esrever"
python
"reverse me"[::-1]
csharp
var str = "reverse me";
Console.WriteLine(new String(str.Reverse().ToArray()));
java
String reverse = new StringBuffer("reverse me").reverse().toString();
String reverse = new StringBuilder("reverse me").reverse().toString();
String reverse = StringUtils.reverse("reverse me");
erlang
Reversed = lists:reverse("reverse me"),
Reversed = revchars("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());

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"
python
' '.join(reversed("This is a end, my only friend!".split()))
csharp
var str = "This is a end, my only friend!";
str = String.Join(" ", str.Split().Reverse().ToArray());
Console.WriteLine(str);
java
List list = new ArrayList();
StringTokenizer st = new StringTokenizer(text, " ");
while(st.hasMoreTokens()) {
list.add(0, st.nextToken());
}
StringBuffer sb = new StringBuffer();
for (Iterator iterator = list.iterator(); iterator.hasNext();) {
String word = (String) iterator.next();
sb.append(word);
if (iterator.hasNext()) {
sb.append(" ");
}
}
String reversed = sb.toString();
List<String> ls = Arrays.asList("This is the end, my only friend!".split("\\s"));
Collections.reverse(ls);
StringBuilder sb = new StringBuilder(32); for (String s : ls) sb.append(" ").append(s);
String reversed = sb.toString().trim();
String reversed = StringUtils.reverseDelimited("This is the end, my only friend!", ' ');
erlang
Reversed = string:join(lists:reverse(string:tokens("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();

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.
python
import textwrap
print textwrap.fill("The quick brown fox jumps over the lazy dog. " * 10,
72, initial_indent="> ", subsequent_indent="> ")
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));
}
}
java
String prefix = "> "; String input = "The quick brown fox jumps over the lazy dog.";

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

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

Remove leading and trailing whitespace from a string

Given the string "  hello    " return the string "hello".
python
assert 'hello' == ' hello '.strip()
csharp
string str = " hello ";
str = str.Trim();
Console.WriteLine(str);
java
String s = " hello "; String trimmed = s.trim();
erlang
Trimmed = string:strip(S),
cpp
String^ s = " hello "; String^ trimmed = s->Trim();

Make a string uppercase

Transform "Space Monkey" into "SPACE MONKEY"
python
"Space Monkey".upper()
csharp
string output = "Space Monkey"

System.Console.WriteLine(output.ToUpper())
java
String upper = text.toUpperCase();
erlang
io:format("~s~n", [string:to_upper("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);

Make a string lowercase

Transform "Caps ARE overRated" into "caps are overrated"
python
"Caps ARE overRated".lower()
csharp
string str = "Caps ARE overRated";
str = str.ToLower() ;
Console.WriteLine(str);
java
"Caps ARE overRated".toLowerCase();
erlang
io:format("~s~n", [string:to_lower("Caps ARE overRated")]).
cpp
std::string s = "Caps ARE overRated";
std::string sl(boost::to_lower_copy(s));
String(L"Caps ARE overRated").ToLower();

Capitalise the first letter of each word

Transform "man OF stEEL" into "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()
csharp
System.Threading.Thread.CurrentThread.CurrentCulture.TextInfo.ToTitleCase("man OF stEEL".ToLowerInvariant());
java
String input = "man OF stEEL";
StringTokenizer tokenizer = new StringTokenizer(input);
StringBuffer sb = new StringBuffer();
while (tokenizer.hasMoreTokens()) {
String word = tokenizer.nextToken();
sb.append(word.substring(0, 1).toUpperCase());
sb.append(word.substring(1).toLowerCase());
sb.append(' ');
}
String text = sb.toString();
StringBuilder sb = new StringBuilder("man OF stEEL"); String s = sb.toString();
int last = s.length() - 1;

for (int i = 0; i <= last; ++i)
if (Character.isSpaceChar(s.charAt(i)) && i < last) { ++i; sb.setCharAt(i, Character.toUpperCase(s.charAt(i))); }
else if (i == 0) sb.setCharAt(i, Character.toUpperCase(s.charAt(i)));
else sb.setCharAt(i, Character.toLowerCase(s.charAt(i)));
Matcher m = Pattern.compile("(\\w+)").matcher("man OF stEEL"); StringBuffer sb = new StringBuffer(32), rsb = new StringBuffer(8);

while (m.find())
{
rsb.replace(0, rsb.length(), m.group().toLowerCase()); rsb.setCharAt(0, Character.toUpperCase(rsb.charAt(0)));
m.appendReplacement(sb, rsb.toString());
}
m.appendTail(sb);
String text = WordUtils.capitalizeFully("man OF stEEL");
erlang
Caps = string:join(lists:map(fun(S) -> to_caps(S) end, string:tokens("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();

Find the distance between two points

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)
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)));
java
double distance = Point2D.distance(x1, y1, x2, y2);
Point2D point1 = new Point2D.Double(x1, y1);
Point2D point2 = new Point2D.Double(x2, y2);
double distance = point1.distance(point2);
double distance = Math.hypot(x2-x1, y2-y1);
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]).
cpp
Point p1 = {34, 78}, p2 = {67, -45};
double distance = ::distance(p1, p2);
Console::WriteLine("{0,3:F2}", distance);

Zero pad a number

Given the number 42, pad it to 8 characters like 00000042
python
"%08d" % 42
csharp
string.Format("{0,8:D8}", 42);
java
String formatted = new DecimalFormat("00000000").format(42);
String formatted = String.format("%08d", 42);
erlang
Formatted = io_lib:format("~8..0B", [42]),
io:format("~8..0B~n", [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;

Right Space pad a number

Given the number 1024 right pad it to 6 characters "1024  "
python
"%-6s" % 1024
str(1024).rjust(6)
'{0: <6}'.format(1024)
csharp
public class NumberRightPadding {
public static void Main() {
string withStringDotFormat = string.Format("{0,-6}", 1024);
string withToStringDotPadRight = 1024.ToString().PadRight(6);
}
}
java
private static String spaces(int spaces) {
StringBuffer sb = new StringBuffer();
for(int i=0; i<spaces; i++) {
sb.append(' ');
}
return sb.toString();
}

private static String rightPad(int number, int spaces) {
String numberString = String.valueOf(number);
return numberString + spaces(spaces - numberString.length());
}
String text = StringUtils.rightPad(String.valueOf(1024), 6)
String formatted = String.format("%-6d", 1024);
erlang
Formatted = io_lib:format("~-6B", [1024]),
io:format("~-6B~n", [1024]).
cpp
String^ formatted = Convert::ToString(1024)->PadRight(6);
String^ formatted = String::Format("{0,-6:D}", 1024);
std::printf("%-6d\n", 1024);
std::ostringstream os;
os << std::setw(6) << std::setfill(' ') << std::left << 1024 << std::ends;
std::cout << os.str() << std::endl;
std::cout << boost::format("%|-6|") % 1024 << std::endl;

Format a decimal number

Format the number 7/8 as a decimal with 2 places: 0.88
python
"%.2f" % (7 / 8.0)
round(7./8., 2)
csharp
public class FormatDecimal {
public static void Main() {
decimal result = decimal.Round( 7 / 8m, 2);
System.Console.WriteLine(result);
}
}
java
String formatted = String.format("%3.2f", 7./8.);
erlang
Formatted = io_lib:format("~.2f", [7/8]),
io:format("~.2f~n", [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;

Left Space pad a number

Given the number 73 left pad it to 10 characters "        73"
python
"%10s" % 73
csharp
public class NumberLeftPadding {
public static void Main() {
string withStringDotFormat = string.Format("{0,10}", 73);
string withToStringDotPadLeft = 73.ToString().PadLeft(10);
}
}
java
private static String spaces(int spaces) {
StringBuffer sb = new StringBuffer();
for(int i=0; i<spaces; i++) {
sb.append(' ');
}
return sb.toString();
}

private static String leftPad(int number, int spaces) {
String numberString = String.valueOf(number);
return spaces(spaces - numberString.length()) + numberString;
}
String formatted = String.format("%10d", 73);
erlang
Formatted = io_lib:format("~10B", [73]),
io:format("~10B~n", [73]).
cpp
String^ formatted = Convert::ToString(73)->PadLeft(10);
String^ formatted = String::Format("{0,10:D}", 73);
std::printf("%10d\n", 73);
std::ostringstream os;
os << std::setw(10) << std::setfill(' ') << 73 << std::ends;
std::cout << os.str() << std::endl;
std::cout << boost::format("%|10|") % 73 << std::endl;

Generate a random integer in a given range

Produce a random integer between 100 and 200 inclusive
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)
csharp
System.Random r = new System.Random();
int random = r.Next(100,201);
java
Random random = new Random();
int randomInt = random.nextInt(200-100+1)+100;
erlang
RandomInt = gen_rand_integer(100, 200),
cpp
Random^ rnd = gcnew Random;
int rndInt = rnd->Next(100, 201);
std::srand(std::time(NULL));

unsigned lb = 100, ub = 200;
unsigned rnd = lb + (rand() % ((ub - lb) + 1));
typedef boost::uniform_int<> Distribution;
typedef boost::mt19937 RNG;

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

unsigned rnd = generator();

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.
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)
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());
}
}

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

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

Check if a string matches a regular expression

Display "ok" if "Hello" matches /[A-Z][a-z]+/
python
found = re.match(r'[A-Z][a-z]+', 'Hello')
if found:
print 'ok'
csharp
if (Regex.IsMatch("Hello", "[A-Z][a-z]+"))
{
Console.WriteLine("ok");
}
java
if ("Hello".matches("[A-Z][a-z]+")) {
System.out.println("ok");
}
erlang
String = "Hello", Regexp = "[A-Z][a-z]+",
is_match(String, Regexp) andalso (begin io:format("ok~n"), true end).
case re:run("Hello", "[A-Z][a-z]+") of {match, _} -> ok end.
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;

Check if a string matches with groups

Display "two" if "one two three" matches /one (.*) three/
python
match = re.match(r'one (.*) three', 'one two three')
if match:
print match.group(1)
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]);
}
}
java
Pattern pattern = Pattern.compile("one (.*) three");
Matcher matcher = pattern.matcher("one two three");
if (matcher.matches()) {
System.out.println(matcher.group(1));
}
erlang
case re:run("one two three", "one (.*) three", [{capture, [1], list}]) of {match, Res} -> hd(Res) end.
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;

Check if a string contains a match to a regular expression

Display "ok" if "abc 123 @#$" matches /\d+/
python
found = re.search(r'\d+', 'abc 123 @#$')
if found:
print 'ok'
csharp
if(System.Text.RegularExpressions.Regex.IsMatch("abc 123 @#$",@"\d+")){
Console.WriteLine("ok");
}
java
Pattern pattern = Pattern.compile("\\d+");
Matcher matcher = pattern.matcher(text);
if (matcher.find()) {
System.out.println("ok");
}
erlang
% Erlang uses 'egrep'-compatible regular expressions, so shortcuts like '\d' not supported
String = "abc 123 @#$", Regexp = "[0-9]+",
is_match(String, Regexp) andalso (begin io:format("ok~n"), true end).
case re:run("abc 123 @#$", "\\d+") of {match, _} -> ok end.
cpp
if (Regex::IsMatch("abc 123 @#$", "\\d+")) Console::WriteLine("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+)/
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"))
csharp
using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

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

class Test
{
static void Main()
{
IList<string> list = "(fish):1 sausage (cow):3 tree (boat):4".Map(@"\((\w+)\):(\d+)", (m) => {return m.Groups[1].Value + m.Groups[2].Value;});
}
}
java
List list = new ArrayList();
Pattern pattern = Pattern.compile("\\((\\w+)\\):(\\d+)");
Matcher matcher = pattern.matcher(text);
while(matcher.find()) {
list.add(matcher.group(1)+matcher.group(2));
}
erlang
solve(S) ->
R = "\\((\\w+?)\\):(\\d+)",
{match, M} = re:run(S,R, [global, {capture, all_but_first, list}]),
[ A++N || [A, N] <- M].
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();
}

Replace all regex matches in a string with a static string

Transform "She sells sea shells" into "She X X shells" by replacing /se\w+/ with "X"
python
transformed = re.sub(r'se\w+', 'X', 'She sells sea shells')
csharp
using System.Text.RegularExpressions;

class SolutionXX
{
static void Main()
{
string text = "She sells sea shells";
string result = Regex.Replace(text, @"se\w+", "X");
}
}
java
String replaced = text.replaceAll("se\\w+", "X");
erlang
% Erlang uses 'egrep'-compatible regular expressions, so shortcuts like '\w' not supported
{ok, Replaced, _} = regexp:gsub("She sells sea shells", "se[A-Za-z0-9_]+", "X"),
re:replace("She sells sea shells", "se\\w+", "X", [global, {return, list}]).
cpp
String^ Replaced = (gcnew Regex("se\\w+"))->Replace("She sells sea shells", "X");
String^ Replaced = Regex::Replace("She sells sea shells", "se\\w+", "X");

Define an empty list

Assign the variable "list" to a list with no elements
python
list = []
csharp
var list = new List<object>();
java
List list = Collections.emptyList();
String[] list = {};
erlang
List = [],
cpp
Generic::List<String^>^ list = gcnew Generic::List<String^>();
std::list<std::string> list;

Define a static list

Define the list [One, Two, Three, Four, Five]
python
list = ['One', 'Two', 'Three', 'Four', 'Five']
print list
csharp
IList<string> list = new string[]{"One","Two","Three","Four","Five"};
java
List<String> numbers = new ArrayList<String>();
Collections.addAll(numbers, "One", "Two", "Three", "Four", "Five");
List numbers = new ArrayList();
numbers.add("One");
numbers.add("Two");
numbers.add("Three");
numbers.add("Four");
numbers.add("Five");
List numbers = Arrays.asList(new String[]{"One", "Two", "Three", "Four", "Five"});
String[] numbers = {"One", "Two", "Three", "Four", "Five"};
List numbers = new ArrayList(){{put("One"); put("Two"); put("Three"); put("Four"); put("Five"); }};
erlang
List = [one, two, three, four, five],
List = ['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";

Join the elements of a list, separated by commas

Given the list [Apple, Banana, Carrot] produce "Apple, Banana, Carrot"
python
print ", ".join(['Apple', 'Banana', 'Carrot'])
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()) );
}
}
java
StringBuffer sb = new StringBuffer();
for (Iterator it = fruit.iterator(); it.hasNext();) {
sb.append(it.next());
if (it.hasNext()) {
sb.append(", ");
}
}
String result = sb.toString();
StringBuilder sb = new StringBuilder(fruit.get(0));
for (String item : fruit.subList(1, fruit.size())) sb.append(", ").append(item);
String result = sb.toString();
String result = StringUtils.join(fruit, ", ");
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)]]).
cpp
String^ result = String::Join(L", ", fruit->ToArray());
string fruits[] = {"Apple", "Banana", "Carrot"};
string result = boost::algorithm::join(fruits, ", ");

Join the elements of a list, in correct english

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

public class CSharpListToEnglishList {
public string JoinAsEnglishList (List<string> words) {
switch (words.Count) {
case 0: return "";
case 1: return words[0];
case 2: return string.Format("{0} and {1}", words.ToArray());
default:
return JoinAsEnglishList( new List<string>() {
string.Join(", ", words.Take(words.Count - 1).ToArray()) + ",",
words.Last()
});
}
}
// Driver...
public static void Main() {
var joiner = new CSharpListToEnglishList();
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Apple", "Banana", "Carrot", "Orange" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Apple", "Banana", "Carrot" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "One", "Two" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Lonely" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>()) );
}
}
java
private String join(List elements) {
if (elements == null || elements.size() == 0) {
return "";
} else if (elements.size() == 1) {
return elements.get(0).toString();
} else if (elements.size() == 2) {
return elements.get(0) + " and " + elements.get(1);
}
StringBuffer sb = new StringBuffer();
for (Iterator it = elements.iterator(); it.hasNext();) {
String next = (String) it.next();
if (sb.length() > 0) {
if (it.hasNext()) {
sb.append(", ");
} else {
sb.append(", and ");
}
}
sb.append(next);
}
return sb.toString();
}
System.out.println(join(fruit));
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)].

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);
}
}

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

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

for (int number : numbers)
for (String letter : letters)
combinations.add(letter + ":" + Integer.toString(number));
SortedSet<AbstractMap.SimpleImmutableEntry<String, Integer> > combinations =
new TreeSet<AbstractMap.SimpleImmutableEntry<String, Integer> >(new CombinationComparator());

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

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;

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

var duplicates = values
.GroupBy(i => i)
.Where(j => j.Count() > 1)
.Select(s => s.Key);
foreach (var duplicate in duplicates)
{
Console.WriteLine(duplicate);
}
java
List listOfDuplicates = new ArrayList(Arrays.asList(new String[]{"andrew", "bob", "chris", "bob"}));

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

Fetch an element of a list by index

Given the list [One, Two, Three, Four, Five], fetch the third element ('Three')
python
list = ['One', 'Two', 'Three', 'Four', 'Five']
list[2]
csharp
string[] items = new string[] { "One", "Two", "Three", "Four", "Five" };
List<string> list = new List<string>(items);
string third = list[2]; // "Three"
// Make sure you import the System.Linq namespace.
// This is not the preferred way of indexing if you are using Lists.
string[] items = new string[] { "One", "Two", "Three", "Four", "Five" };
IEnumerable<string> list = new List<string>(items);
string third = list.ElementAt(2); // Three
java
String result = list.get(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),
cpp
String^ result = list[2];

Fetch the last element of a list

Given the list [Red, Green, Blue], access the last element ('Blue')
python
list = ['Red', 'Green', 'Blue']
list[-1]
csharp
string[] items = new string[] { "Red", "Green", "Blue" };
List<string> list = new List<string>(items);
string last = list[list.Count - 1]; // "Blue"
// Make sure you import the System.Linq namespace.
// This is not the preferred way of finding the last element if you are using Lists.
string[] items = new string[] { "Red", "Green", "Blue" };
IEnumerable<string> list = new List<string>(items);
string last = list.Last(); // "Blue"
java
String result = list.get(list.size() - 1);
erlang
Result = lists:last(List),
Result = last(List),
Result = hd(lists:reverse(List)),
Result = lists:nth(length(List), List),
cpp
String^ result = list[list->Count - 1];
string last_elem = lst.back();

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

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

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

unique_ages = list(set(ages))
csharp
using System.Collections.Generic;
using System.Linq;
public class UniqueElements {
public static void Main() {
var list = new List<int>() { 18, 16, 17, 18, 16, 19, 14, 17, 19, 18 };
var uniques = list.Distinct();
}
}
java
Set<Integer> ages = new TreeSet<Integer>(Arrays.asList(new Integer[]{18, 16, 17, 18, 16, 19, 14, 17, 19, 18}));

System.out.println(ages);
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]).
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"));

Remove an element from a list by index

Given the list [Apple, Banana, Carrot], remove the first element to produce the list [Banana, Carrot]
python
myList = ['Apple', 'Banana', 'Carrot']
print myList
del myList[0]
# or
myList.pop(0) # returns 'Apple'
print myList
csharp
class Solution1516
{
static void Main()
{
List<string> fruit = new List<string>() { "Apple", "Banana", "Carrot" };
fruit.RemoveAt(0);
}
}
java
list.remove(0);
erlang
Result = tl(List),
[_|Result] = List,
N = 1, {Left, Right} = lists:split(N - 1, List), Result = Left ++ tl(Right),
Result = drop(1, List),
cpp
fruit->RemoveAt(0);

Remove the last element of a list

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

csharp
List<string> fruits = new List() { "apple", "banana", "cherry" };
fruits.RemoveAt(fruits.Length - 1);
java
list.remove(list.size() - 1);
erlang
Result = init(List),
Result = take(length(List) - 1, List),
Result = lists:reverse(tl(lists:reverse(List))),
cpp
fruit->RemoveAt(fruit->Count - 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"]
python
l = ["apple", "orange", "grapes", "bananas"]
first, l = l[0], l[1:] + l[:1]
fruit = ['apple', 'orange', 'grapes', 'bananas']
fruit.append(fruit.pop(0))
csharp
var lst = new LinkedList<String>(new String[] {"apple", "orange", "grapes", "banana"});
lst.AddLast(lst.First());
lst.DeleteFirst();
java
list.add(list.remove(0));
Collections.rotate(list, -1);
erlang
N = 1, {Left, Right} = lists:split(N, List), Result = Right ++ Left,
N = 1, Result = rotate(N, List),
cpp
fruit->Add(fruit[0]); fruit->RemoveAt(0);
rotate(fruit.begin(), fruit.begin()+1, fruit.end());

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

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

String[] result = zip(",", list);
erlang
First = ['Bruce', 'Tommy Lee', 'Bruce'], Last = ['Willis', 'Jones', 'Lee'], Years = [1955, 1946, 1940],

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

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'.
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
csharp
using System;
using System.Collections.Generic;
using System.Linq;

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

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

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

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

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

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

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

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

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

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

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;

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]
python
print map(lambda x: len(x), ["ox", "cat", "deer", "whale"])
print [len(x) for x in ['ox', 'cat', 'deer', 'whale']]
csharp
using System.Collections.Generic;
public class OperationOnEach {
public static void Main() {
var list = new List<string>() { "ox", "cat", "deer", "whale" };
list.ForEach( System.Console.WriteLine );
}
}
java
public class SolutionXX {
public static void main(String[] args) {
String[] list = {"ox", "cat", "deer", "whale"};
for (String str : list) {
System.out.println(str.length() + " ");
}
}
}
erlang
lists:map(fun (X) ->length(X) end, List).
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(); });

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

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


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

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

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

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

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
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)
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));
java
Map map = new HashMap();
for (Iterator it = list.iterator(); it.hasNext();) {
String s = (String) it.next();
if (!map.containsKey(s)) {
map.put(s, new Integer(1));
} else {
map.put(s, new Integer(((Integer)map.get(s)).intValue() + 1));
}
}
LinkedMap histogram = new LinkedMap();

for (Object letter : list)
histogram.put(letter, !histogram.containsKey(letter) ? 1 : MapUtils.getIntValue(histogram, letter) + 1);
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])).
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;

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
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)
csharp
using System.Collections.Generic;
using System.Linq;
public class ListCategorizer {
public static void Main() {
var list = new List<string>() { "one", "two", "three", "four", "five" };
var categories = list.GroupBy(el => el.Length)
.ToDictionary( g => g.Key, // key
g => g.ToList() ); // value
}
}
java
SortedMap<Integer, List<String> > map = new TreeMap<Integer, List<String> >(); int key; List<String> vlist;

for (String item : list)
{
key = item.length(); vlist = map.containsKey(key) ? map.get(key) : new ArrayList<String>();
vlist.add(item); map.put(key, vlist);
}
MultiValueMap map = new MultiValueMap();
for (Object item : list) map.put(((String) item).length(), item);
erlang
% Imperative Solution
CatList = categorise(List),
% Functional (1) Solution
CatList = categorise(List),
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);
}

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.
python
if name == 'Bob':
print 'Hello, Bob!'
csharp
if (name == "Bob") Console.WriteLine("Hello, {0}!", name);
java
if (name.equals("Bob")) {
System.out.println("Hello, Bob!");
}
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).
cpp
if (name == "Bob") Console::WriteLine("Hello, {0}!", name);
if (name == "Bob") std::cout << "Hello, " << name << "!" << std::endl;

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"
python
if age > 42:
print 'You are old'
else:
print 'You are young'
print age > 42 and 'You are old' or 'You are young'
csharp
int age = 41;

if (age > 42)

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


java
if (age > 42) {
System.out.println("You are old");
} else {
System.out.println("You are young");
}
System.out.println("You are " + ((age>42)?"old":"young"));
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]).
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"));

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

python
if age > 84:
print 'You are really ancient'
elif age > 30:
print 'You are middle-aged'
else:
print 'You are young'
csharp
if (age > 84) Console.WriteLine("You are really ancient");
else if (age > 30) Console.WriteLine("You are middle-aged");
else Console.WriteLine("You are young");
Console.WriteLine("You are {0}", ((age > 84) ? "really ancient" : (age > 30) ? "middle-aged" : "young"));
java
if (age > 84) System.out.println("You are really ancient");
else if (age > 30) System.out.println("You are middle-aged");
else System.out.println("You are young");
erlang
if
Age > 84 -> io:format("You are really ancient~n");
Age > 30 -> io:format("You are middle-aged~n");
true -> io:format("You are young~n")
end.
case Age of
_ when Age > 84 -> io:format("You are really ancient~n");
_ when Age > 30 -> io:format("You are middle-aged~n");
true -> io:format("You are young~n")
end.
cpp
if (age > 84) Console::WriteLine("You are really ancient");
else if (age > 30) Console::WriteLine("You are middle-aged");
else Console::WriteLine("You are young");
Console::WriteLine("You are {0}", (age > 84 ? "really ancient" : age > 30 ? "middle-aged" : "young"));
std::cout << "You are " << (age > 84 ? "really ancient" : age > 30 ? "middle-aged" : "young") << std::endl;

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
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)]

csharp
public static string GetOrdinal(int i)
{
if (i > 10 && i < 20) return i.ToString() + "th";
switch (i % 10)
{
case 1:
return i.ToString() + "st";
case 2:
return i.ToString() + "nd";
case 3:
return i.ToString() + "rd";
default:
return i.ToString() + "th";
}
}
public static string GetOrdinal(int i)
{
if (i > 10 && i < 20) return i.ToString() + "th";
switch (i % 10)
{
case 1:
return i.ToString() + "st";
break;
case 2:
return i.ToString() + "nd";
break;
case 3:
return i.ToString() + "rd";
break;
default:
return i.ToString() + "th";
break;
}
}
java
String[] array = new String[40];
for(int n = 1; n <= array.length; n++)
array[n-1] = Integer.toString(n);
for(int n = 0; n < array.length; n++)
{
int y = Integer.parseInt(array[n]);
if(array[n].length() > 1)
y = Integer.parseInt(array[n].substring(1));
switch(y)
{
case 1: {array[n] += "st"; break;}
case 2: {array[n] += "nd"; break;}
case 3: {array[n] += "rd"; break;}
default: array[n] += "th";
}
}
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])
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();
}

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.
python
x = 1
while x < 150:
print '%s, ' % x,
x *= 2
csharp
int x = 1;

while (x < 150)
{
x *= 2;
Console.Write("{0},", x);
}
java
int x = 1;
while (x < 150) {
System.out.println(x+",");
x*=2;
}
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).
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;

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

do
{
roll = die.Next(1, 6);
Console.Write(roll);
if (roll < 6) Console.Write(",");
}
while (roll != 6);
java
int rnd;
do {
rnd = (int)(Math.random()*6)+1;
System.out.print(rnd);
if (rnd!=6) {
System.out.print(",");
}
} while(rnd!=6);
erlang
Pred = fun (DiceRoll) -> DiceRoll =/= 6 end,
Action = fun (DiceRoll) -> io:format("~B,", [DiceRoll]), dice_roll() end,

do_while(Pred, Action, dice_roll()).
-module(dice).
-export([start/0]).

start() ->
roll(dice_roll()).

roll(6) ->
io:format("6~n", []);
roll(N) ->
io:format("~B,", [N]),
roll(dice_roll()).

dice_roll() -> random:uniform(6).
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();

Perform an action a fixed number of times (FOR)

Display the string "Hello" five times like "HelloHelloHelloHelloHello"
python
print "Hello" * 5
for i in range(5):
print "Hello"
csharp
string text = "Hello";

for (int i = 0; i < 5; i++)
{
Console.Write(text);
}
java
for(int i=0;i<5;i++) {
System.out.print("Hello");
}
erlang
dotimes(5, fun () -> io:format("Hello") end).
lists:foreach(fun (_) -> io:format("Hello") end, lists:seq(1, 5)).
cpp
for(int i = 0; i < 5; ++i) Console::Write("Hello");
for(int i = 5; i > 0; --i) Console::Write("Hello");
dotimes(5, hello);
fill_n(ostream_iterator<string>(cout), 5, "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!"
python
print " .. ".join(str(i) for i in range(10, 0, -1)), ".. liftoff!"
csharp
for (int i = 10; i > 0; i--)
{
Console.Write("{0} .. ", i);
}

Console.WriteLine("Liftoff!");
java
for(int i=10; i>=1; i--) {
System.out.print(i + " .. ");
}
System.out.print("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").
cpp
for(int i = 10; i != 0; --i) Console::Write("{0} .. ", i);
Console::WriteLine("Liftoff!");

Read the contents of a file into a string

python
contents = open('myFile.txt', 'rt').read()
csharp
string contents = System.IO.File.ReadAllText("filename.txt");
java
String text = FileUtils.readFileToString(new File("Solution109.java"), "UTF-8");
RandomAccessFile raf = null; byte[] buffer; String text = null;

try
{
raf = new RandomAccessFile("Solution399.java", "r");
buffer = new byte[(int)raf.length()]; raf.read(buffer);
text = new String(buffer);
}
erlang
Text = readfile("Solution607.erl"),
Text = readfile("Solution608.erl"),
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");

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
python
for no, line in enumerate(open(__file__)):
print "{0}> {1}".format(no+1, line.rstrip())
csharp
int counter = 0;

// If the file is large, you would want to buffer this instead of reading everything at once
foreach (string line in System.IO.File.ReadAllLines("filename.txt"))
{
Console.WriteLine("{0}> {1}", ++counter, line);
}
java
BufferedReader br = null;
try {
br = new BufferedReader(new FileReader("Solution104.java"));
String line = null;
int lineNumber = 1;
while ((line=br.readLine())!=null) {
System.out.println(lineNumber + "> " + line);
lineNumber++;
}
} catch (IOException e) {
throw new RuntimeException(e);
} finally {
if (br!=null) {
try {
br.close();
} catch (Exception e) {
// ok
}
}
}
LineNumberReader lnr = null; PrintWriter pw = null; String line;

try
{
lnr = new LineNumberReader(new FileReader("Solution400.java"));
pw = new PrintWriter(System.out);
while ((line = lnr.readLine()) != null) pw.printf("%d> %s\n", lnr.getLineNumber(), line);
}
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).
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);

Write a string to a file

python
open('test.txt', 'wt').write('Hello World!')
csharp
System.IO.File.WriteAllText("filename.txt", "Some text to write to the file");
java
FileWriter fw = null;

try
{
fw = new FileWriter("test.txt");
fw.write("This line overwites file contents!");
}
PrintWriter pw = null;

try
{
pw = new PrintWriter(new BufferedWriter(new FileWriter("test.txt")));
pw.print("This line overwites file contents!");
}
erlang
Line = "This line overwites file contents!\n",
{ok, IODevice} = file:open("test.txt", [write]), file:write(IODevice, Line), file:close(IODevice).
cpp
IO::StreamWriter^ stream;

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

Append to a file

python
open('test.txt', 'at').write('Hello World!\n')
csharp
System.IO.File.AppendAllText("filename.txt", "Some text to append to the file");
java
FileWriter fw = null;

try
{
fw = new FileWriter("test.txt", true);
fw.write("This line appended to file!");
}
PrintWriter pw = null;

try
{
pw = new PrintWriter(new BufferedWriter(new FileWriter("test.txt", true)));
pw.print("This line appended to file!");
}
erlang
Line = "This line appended to file!\n",
{ok, IODevice} = file:open("test.txt", [append]), file:write(IODevice, Line), file:close(IODevice).
cpp
IO::StreamWriter^ stream;

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

Process each file in a directory

python
import os
results = (process(f) for f in os.listdir(".") if os.path.isfile(f))
csharp
foreach (string filename in System.IO.Directory.GetFiles(directory)) ProcessFile(filename);
java
for (File file : (new File("c:\\")).listFiles()) process(file);
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)).
cpp
for each(String^ filename in IO::Directory::GetFiles(dirname)) process(filename);

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.
python
import time
time.strptime("2008-05-06 13:29", "%Y-%m-%d %H:%M")
csharp
DateTime parsedDate = DateTime.Parse("2008-05-06 13:29");
// Ideally, you would catch the potential FormatException or use DateTime.TryParse in production code.
java
DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm");
Date date = df.parse("2008-05-06 13:29");
DateTimeFormatter fmt = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm");
DateTime dt = fmt.parseDateTime("2008-05-06 13:29");
erlang
% AFAIK, no datetime-parsing library exists; 'parse_to_datetime' is a simplistic, problem-specific hack
LocalDateTime = erlang:universaltime_to_localtime(parse_to_datetime("2008-05-06 13:29:34")),
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);

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.
python
from datetime import datetime
print datetime.utcnow()
csharp
// Creating a variable first:
DateTime now = DateTime.Now;
Console.WriteLine(now);

// Without creating a variable:
Console.WriteLine(DateTime.Now);
java
import java.util.Date;

public class SolutionXX {
public static void main(String[] args) {
Date now = new Date();
System.out.println(now.toString());
}
}
erlang
io:format("~p~n", [calendar:local_time()])
cpp
QDate now = QDate::currentData();
qDebug() << now.toString();
time_t date = time(0);
cout << ctime(&date);
OOP

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

Greeter("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();
}
}
java
class Greeter
{
public Greeter(String whom) { this.whom = whom; }
public void greet() { System.out.printf("Hello, %s\n", whom); }
private String whom;
}

public class Solution381 {
public static void main(String[] args) {
(new Greeter("world")).greet();
}
}
erlang
Greeter = make_greeter("world!"),
Greeter(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);
}
XML

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. $14.50
python
from xml.dom.minidom import parseString
document = parseString(
"""<shopping>
<item name="bread" quantity="3" price="2.50"/>
<item name="milk" quantity="2" price="3.50"/>
</shopping>""").documentElement
total = sum([float(item.getAttribute('price')) *
int(item.getAttribute('quantity'))
for item in document.getElementsByTagName('item')])
print '$%.2f' % total
csharp
System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
doc.LoadXml(
@"<shopping>
<item name='bread' quantity='3' price='2.50'/>
<item name='milk' quantity='2' price='3.50'/>
</shopping>");

string decimalSeparator= System.Globalization.CultureInfo.CurrentCulture.NumberFormat.CurrencyDecimalSeparator;

double sum=0;

foreach(System.Xml.XmlNode nodo in doc.SelectNodes("/shopping/item")){
sum += int.Parse(nodo.Attributes["quantity"].InnerText) * double.Parse(nodo.Attributes["price"].InnerText.Replace(".",decimalSeparator));
}
Console.WriteLine("{0:#.00}",sum);
java
// solution uses JAXP and SAX included in Java API since version >= 1.5
class ShoppingContentHandler extends DefaultHandler {
Double priceSum = 0d;
@Override
public void startElement(String uri, String localName, String name,
Attributes attributes) throws SAXException {
if(name.equals("item")) {
String quantityString = attributes.getValue(attributes.getIndex("quantity"));
String priceString = attributes.getValue(attributes.getIndex("price"));
Integer quantity = Integer.parseInt(quantityString);
Double price = Double.parseDouble(priceString);
priceSum += (quantity * price);
}
}
public Double getPriceSum() {
return priceSum;
}
}

SAXParserFactory parserFactory = SAXParserFactory.newInstance();
try {
SAXParser parser = parserFactory.newSAXParser();
XMLReader reader = parser.getXMLReader();
ShoppingContentHandler contentHandler = new ShoppingContentHandler();
reader.setContentHandler(contentHandler);
reader.parse(new InputSource(new FileReader("shopping.xml")));
System.out.printf("$%.2f", contentHandler.getPriceSum());

} catch (ParserConfigurationException e) {
e.printStackTrace();
} catch (SAXException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
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]).
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;

create some XML programmatically

Given the following CSV:

bread,3,2.50
milk,2,3.50

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

<shopping>
  <item name="bread" quantity="3" price="2.50" />
  <item name="milk" quantity="2" price="3.50" />
</shopping>
python
from xml.dom import minidom

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

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

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

print shopping.toprettyxml()
from xml.etree.ElementTree import Element, SubElement, tostring

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

root = Element('shopping')

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

print tostring(root)
csharp
string cvs ="bread,3,2.50\nmilk,2,3.50";
IList<string> rows = cvs.Split('\n');

System.Text.StringBuilder sb = new System.Text.StringBuilder("<shopping>");
foreach(string row in rows){
IList<string> data = row.Split(',');
sb.AppendFormat("<item name='{0}' quantity='{1}' price='{2}' />",data[0],data[1],data[2]);
}
sb.Append("</shopping>");
java
// In this solution JAXB is used to created the xml output.
// JAXB is included in Java 1.6. Runs with 1.5 if you include JAXB Jars
// in the classpath.
class Item {
// Of course you use getters and setters and declare attributes private.
// In this sample a "dirty" way is chosen to keep LOC low.
@XmlAttribute
String name;
@XmlAttribute
Integer quantity;
@XmlAttribute
Double price;
}

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

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

}
JAXB.marshal(shopping, "D:" + File.separatorChar + "shopping.auto.xml");
} catch (IOException e) {
e.printStackTrace();
}
erlang
to_xml(ShoppingList) ->
Items = lists:map(fun(L) ->
[Name, Quantity, Price] = string:tokens(L, ","),
{item, [{name, Name}, {quantity, Quantity}, {price, Price}], []}
end, string:tokens(ShoppingList, "\n")),
xmerl:export_simple([{shopping, [], Items}], xmerl_xml).
cpp
string input("bread,3,2.50\nmilk,2,3.50\n");

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

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

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

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

cout << doc << endl;

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.

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)
csharp
public static int gcd(int a, int b)
{
if (b == 0)
return a;
else
return gcd(b, a % b);
}
java
static int gcd(int a, int b) {
if (Math.min(a, b) == 0)
return Math.max(a, b);
else
return gcd(Math.min(a, b), Math.abs(a - b));
}
erlang
-module(gcd).
-export([gcd/2]).

gcd(A, 0) -> A;
gcd(A, B) -> gcd(B, A rem B).
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;
}