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!")
clojure
(println "Hello World!")
erlang
io:format("Hello, World!~n").
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'''\#{'}${"}/'''
print "\\#{'}${\"}/"
print "\\#{'}${"'"'"}/"
print r"""\#{'}${"}/"""
print '\\#{\'}${"}/'
print '\\#{'"'"'}${"}/'
print r'''\#{'}${"}/'''
csharp
string verbatim = @"\#{'}${""""}/";
string cStyle = "\\#{'}${\"\"}/";
string cStyle = "\\#{'}${\"\"}/";
clojure
(def special "\\#{'}${\"}/")
erlang
Special = "\\#{'}\${\"}/",
Define a multiline string
Define the string:
"This
Is
A
Multiline
String"
python
text = """This
Is
A
Multiline
String"""
Is
A
Multiline
String"""
# with proper indentation
text = (
"This\n"
"Is\n"
"A\n"
"Multiline\n"
"String"
)
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";
Is
A
Multiline
String";
clojure
(def multiline "This\nIs\nA\nMultiline\nString")
erlang
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())
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)
"%d+%d=%d" % (a, b, a+b)
csharp
int a = 3;
int b = 4;
Console.WriteLine("{0}+{1}={2}", a,b,a+b);
int b = 4;
Console.WriteLine("{0}+{1}={2}", a,b,a+b);
clojure
(format "%d + %d = %d" a b (+ a b))
erlang
A = 3, B = 4,
io:format("~B+~B=~B~n", [A, B, (A+B)]).
io:format("~B+~B=~B~n", [A, B, (A+B)]).
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()));
Console.WriteLine(new String(str.Reverse().ToArray()));
clojure
(require '[clojure.contrib.str-utils2 :as str])
(str/reverse "reverse me")
(str/reverse "reverse me")
(apply str (reverse "reverse me"))
erlang
Reversed = lists:reverse("reverse me"),
Reversed = revchars("reverse me"),
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);
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!" #" ")))
(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!"))))
erlang
Reversed = string:join(lists:reverse(string:tokens("This is the end, my only friend!", " ")), " "),
Text wrapping
Wrap the string
> 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.
"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="> ")
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));
}
}
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))
(apply str
(repeat 10 "The quick brown fox jumps over the lazy dog. ")))]
(println ">" 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")).
lists:foreach(fun (Line) -> io:format("~s~n", [string:concat(Prefix, Line)]) end, string:tokens(TextWrap, "\n")).
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);
str = str.Trim();
Console.WriteLine(str);
clojure
(use 'clojure.contrib.str-utils2)
(trim " hello ")
(trim " hello ")
(clojure.string/trim " hello ")
(.trim " hello ")
erlang
Trimmed = string:strip(S),
Make a string uppercase
Transform
"Space Monkey" into "SPACE MONKEY"
python
"Space Monkey".upper()
csharp
string output = "Space Monkey"
System.Console.WriteLine(output.ToUpper())
System.Console.WriteLine(output.ToUpper())
clojure
(.toUpperCase "Space Monkey")
erlang
io:format("~s~n", [string:to_upper("Space Monkey")]).
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);
str = str.ToLower() ;
Console.WriteLine(str);
clojure
(.toLowerCase "Caps ARE overRated")
erlang
io:format("~s~n", [string:to_lower("Caps ARE overRated")]).
Capitalise the first letter of each word
Transform
"man OF stEEL" into "Man Of Steel"
python
from string import capwords
capwords("man OF stEEL")
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());
clojure
(use 'clojure.contrib.str-utils2)
(join " " (map capitalize (split "man OF stEEL" #" ")))
(join " " (map capitalize (split "man OF stEEL" #" ")))
erlang
Caps = string:join(lists:map(fun(S) -> to_caps(S) end, string:tokens("man OF stEEL", " ")), " "),
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 sqrt
print sqrt(sum((x-y)**2 for x,y in zip(a, b)))
from math import hypot
print hypot(x2-x1, y2-y1)
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)));
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"
[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])
"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])
erlang
Distance = distance({point, 34, 78}, {point, 67, -45}),
io:format("~.2f~n", [Distance]).
io:format("~.2f~n", [Distance]).
Distance = distance(point:new(34, 78), point:new(67, -45)),
io:format("~.2f~n", [Distance]).
io:format("~.2f~n", [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);
clojure
(defn pad
([x] (if (> 8 (.length (str x))) (pad (str 0 x)) (str x)))
)
([x] (if (> 8 (.length (str x))) (pad (str 0 x)) (str x)))
)
(defn pad [x]
(format "%08d" x))
(format "%08d" x))
(format "%08d" 42)
erlang
Formatted = io_lib:format("~8..0B", [42]),
io:format("~8..0B~n", [42]).
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);
}
}
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) " "))))
l (count s)]
(str s (reduce str (repeat (- 6 l) " "))))
erlang
Formatted = io_lib:format("~-6B", [1024]),
io:format("~-6B~n", [1024]).
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);
}
}
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)))))
erlang
Formatted = io_lib:format("~.2f", [7/8]),
io:format("~.2f~n", [7/8]).
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);
}
}
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 ))
l (count s)]
(str (reduce str (repeat (- 10 l) " ")) s ))
erlang
Formatted = io_lib:format("~10B", [73]),
io:format("~10B~n", [73]).
Generate a random integer in a given range
Produce a random integer between 100 and 200 inclusive
python
import random
random.randint(100, 200)
random.randint(100, 200)
# uses best entropy source available (e.g. /dev/urandom, CryptGenRandom, ...)
import random
print random.SystemRandom().randint(100,200)
import random
print random.SystemRandom().randint(100,200)
csharp
System.Random r = new System.Random();
int random = r.Next(100,201);
int random = r.Next(100,201);
clojure
(+ (rand-int (- 201 100)) 100)
erlang
RandomInt = gen_rand_integer(100, 200),
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)
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());
}
}
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))
(let [r (java.util.Random. 12345)]
(dotimes [_ 5]
(println (.nextInt r 100))))
(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))]).
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))]).
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'
if found:
print 'ok'
csharp
if (Regex.IsMatch("Hello", "[A-Z][a-z]+"))
{
Console.WriteLine("ok");
}
{
Console.WriteLine("ok");
}
clojure
(if (re-matches #"[A-Z][a-z]+" "Hello")
(println "ok"))
(println "ok"))
erlang
String = "Hello", Regexp = "[A-Z][a-z]+",
is_match(String, Regexp) andalso (begin io:format("ok~n"), true end).
is_match(String, Regexp) andalso (begin io:format("ok~n"), true end).
case re:run("Hello", "[A-Z][a-z]+") of {match, _} -> ok end.
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)
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]);
}
}
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)))
(println (second groups)))
erlang
case re:run("one two three", "one (.*) three", [{capture, [1], list}]) of {match, Res} -> hd(Res) end.
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 @#$')
if found:
print 'ok'
if found:
print 'ok'
csharp
if(System.Text.RegularExpressions.Regex.IsMatch("abc 123 @#$",@"\d+")){
Console.WriteLine("ok");
}
Console.WriteLine("ok");
}
clojure
(if (re-find #"\d+" "abc 123 @#$")
(println "ok"))
(println "ok"))
erlang
% Erlang uses 'egrep'-compatible regular expressions, so shortcuts like '\d' not supported
String = "abc 123 @#$", Regexp = "[0-9]+",
is_match(String, Regexp) andalso (begin io:format("ok~n"), true end).
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.
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"))
--------------------------------------------------------------------------
(''.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;});
}
}
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;});
}
}
clojure
(let [matcher (re-matcher #"\((\w+)\):(\d+)" "(fish):1 sausage (cow):3 tree (boat):4")]
(loop [match (re-find matcher)
lst []]
(if match
(recur (re-find matcher) (conj lst (str (second match) (nth match 2))))
lst)))
(loop [match (re-find matcher)
lst []]
(if match
(recur (re-find matcher) (conj lst (str (second match) (nth match 2))))
lst)))
erlang
solve(S) ->
R = "\\((\\w+?)\\):(\\d+)",
{match, M} = re:run(S,R, [global, {capture, all_but_first, list}]),
[ A++N || [A, N] <- M].
R = "\\((\\w+?)\\):(\\d+)",
{match, M} = re:run(S,R, [global, {capture, all_but_first, list}]),
[ A++N || [A, N] <- M].
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");
}
}
class SolutionXX
{
static void Main()
{
string text = "She sells sea shells";
string result = Regex.Replace(text, @"se\w+", "X");
}
}
clojure
(.replaceAll (re-matcher #"se\w+" "She sells sea shells") "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"),
{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}]).
Define an empty list
Assign the variable
"list" to a list with no elements
python
list = []
csharp
var list = new List<object>();
clojure
(list)
'()
erlang
List = [],
Define a static list
Define the list
[One, Two, Three, Four, Five]
python
list = ['One', 'Two', 'Three', 'Four', 'Five']
print list
print list
csharp
IList<string> list = new string[]{"One","Two","Three","Four","Five"};
clojure
(def a '[One Two Three Four Five])
erlang
List = [one, two, three, four, five],
List = ['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()) );
}
}
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")))
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)]]).
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(
join(
join(
join(
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(*[]) == ""
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>()) );
}
}
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>()) );
}
}
clojure
(defn join [lst]
(cond
(= (count lst) 0) ""
(= (count lst) 1) (first lst)
(= (count lst) 2) (str (first lst) " and " (second lst))
(> (count lst) 2) (loop [lst lst sb (StringBuilder.)]
(if (empty? lst)
(.toString sb)
(recur (rest lst) (.append sb (cond
(> (count lst) 2) (str (first lst) ", ")
(> (count lst) 1) (str (first lst) ", and ")
(= (count lst) 1) (str (first lst)))))))))
(cond
(= (count lst) 0) ""
(= (count lst) 1) (first lst)
(= (count lst) 2) (str (first lst) " and " (second lst))
(> (count lst) 2) (loop [lst lst sb (StringBuilder.)]
(if (empty? lst)
(.toString sb)
(recur (rest lst) (.append sb (cond
(> (count lst) 2) (str (first lst) ", ")
(> (count lst) 1) (str (first lst) ", and ")
(= (count lst) 1) (str (first lst)))))))))
(defn join
([lst]
(join lst false))
([lst is-long]
(condp = (count lst)
0 ""
1 (first lst)
2 (str (first lst) (if is-long ",") " and " (second lst))
(str (first lst) ", " (join (rest lst) true)))))
([lst]
(join lst false))
([lst is-long]
(condp = (count lst)
0 ""
1 (first lst)
2 (str (first lst) (if is-long ",") " and " (second lst))
(str (first lst) ", " (join (rest lst) true)))))
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).
% ------
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)].
%% 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)].
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])]
[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 });
}
}
}
}
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 });
}
}
}
}
clojure
(defn combine [lst1 lst2]
(mapcat (fn [x] (map #(list % x) lst1)) lst2))
(mapcat (fn [x] (map #(list % x) lst1)) lst2))
(mapcat (fn [x] (map #(list % x) ["a", "b", "c"])) [4, 5])
erlang
Combinations =
lists:foldl(fun (Number, Acc) -> Acc ++ lists:map(fun (Letter) -> {Letter, Number} end, Letters) end, [], Numbers),
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]].
From a List Produce a List of Duplicate Entries
Taking a list:
Write the code to produce a list of duplicates in the 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]
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);
}
var duplicates = values
.GroupBy(i => i)
.Where(j => j.Count() > 1)
.Select(s => s.Key);
foreach (var duplicate in duplicates)
{
Console.WriteLine(duplicate);
}
clojure
(->> '("andrew" "bob" "chris" "bob")
(group-by identity)
(filter #(> (count (second %)) 1))
(map first))
(group-by identity)
(filter #(> (count (second %)) 1))
(map first))
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(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).
([X | Xs], F) -> case lists:member(X, Xs) of
true -> [X | F(Xs, F)];
_ -> F(Xs, F)
end;
([], _) -> []
end,
Result = Fun(List, Fun).
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]
list[2]
csharp
string[] items = new string[] { "One", "Two", "Three", "Four", "Five" };
List<string> list = new List<string>(items);
string third = list[2]; // "Three"
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
// 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)
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),
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]
list[-1]
csharp
string[] items = new string[] { "Red", "Green", "Blue" };
List<string> list = new List<string>(items);
string last = list[list.Count - 1]; // "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"
// 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"
clojure
(last '[One Two Three Four Five])
erlang
Result = lists:last(List),
Result = last(List),
Result = hd(lists:reverse(List)),
Result = lists:nth(length(List), List),
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]
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)
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']
// 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']
clojure
(use 'clojure.set)
(let [beans '[broad mung black red white]
colors '[black red blue green]]
(intersection (set beans) (set colors)))
(let [beans '[broad mung black red white]
colors '[black red blue green]]
(intersection (set beans) (set 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)),
Common = sets:to_list(sets:intersection(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))
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();
}
}
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();
}
}
clojure
;; returns a set
(set [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;#{14 16 17 18 19}
;; returns a lazy sequence of the unique elements
(distinct [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;(18 16 17 19 14)
(set [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;#{14 16 17 18 19}
;; returns a lazy sequence of the unique elements
(distinct [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;(18 16 17 19 14)
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]).
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
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);
}
}
{
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)))
index 0]
(concat
(take index fruit)
(drop (+ index 1) fruit)))
erlang
Result = tl(List),
[_|Result] = List,
N = 1, {Left, Right} = lists:split(N - 1, List), Result = Left ++ tl(Right),
Result = drop(1, List),
Remove the last element of a list
python
myList = ['Apple', 'Banana', 'Carrot']
myList.pop()
myList.pop()
csharp
List<string> fruits = new List() { "apple", "banana", "cherry" };
fruits.RemoveAt(fruits.Length - 1);
fruits.RemoveAt(fruits.Length - 1);
clojure
(pop ["Apple" "Banana" "Carrot"])
erlang
Result = init(List),
Result = take(length(List) - 1, List),
Result = lists:reverse(tl(lists:reverse(List))),
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]
first, l = l[0], l[1:] + l[:1]
fruit = ['apple', 'orange', 'grapes', 'bananas']
fruit.append(fruit.pop(0))
fruit.append(fruit.pop(0))
csharp
var lst = new LinkedList<String>(new String[] {"apple", "orange", "grapes", "banana"});
lst.AddLast(lst.First());
lst.DeleteFirst();
lst.AddLast(lst.First());
lst.DeleteFirst();
clojure
(let [fruit ["apple" "orange" "grapes" "bananas"]]
(concat (rest fruit) [(first fruit)])
(concat (rest fruit) [(first fruit)])
erlang
N = 1, {Left, Right} = lists:split(N, List), Result = Right ++ Left,
N = 1, Result = rotate(N, List),
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)
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)));
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)));
clojure
(defn gatherer [listOfLists]
(if (empty? (first listOfLists))
() ; the base case for recursion
(cons
(map first listOfLists) ; get the first element of each of the lists
(gatherer (map rest listOfLists)) ; gather all the subsequent ones
)
)
)
(def firstnames '("Bruce" "Tommy Lee" "Bruce"))
(def lastnames '("Willis" "Jones" "Lee"))
(def years '(1955 1946 1940))
(println (gatherer [firstnames lastnames years]))
; -> ((Bruce Willis 1955) (Tommy Lee Jones 1946) (Bruce Lee 1940))
(if (empty? (first listOfLists))
() ; the base case for recursion
(cons
(map first listOfLists) ; get the first element of each of the lists
(gatherer (map rest listOfLists)) ; gather all the subsequent ones
)
)
)
(def firstnames '("Bruce" "Tommy Lee" "Bruce"))
(def lastnames '("Willis" "Jones" "Lee"))
(def years '(1955 1946 1940))
(println (gatherer [firstnames lastnames years]))
; -> ((Bruce Willis 1955) (Tommy Lee Jones 1946) (Bruce Lee 1940))
(def firstnames ["Bruce" "Tommy Lee" "Bruce"])
(def lastnames ["Willis" "Jones" "Lee"])
(def years [1955 1946 1940])
(println (map (fn [f l y] [f l y]) firstnames lastnames years))
(def lastnames ["Willis" "Jones" "Lee"])
(def years [1955 1946 1940])
(println (map (fn [f l y] [f l y]) firstnames lastnames years))
erlang
First = ['Bruce', 'Tommy Lee', 'Bruce'], Last = ['Willis', 'Jones', 'Lee'], Years = [1955, 1946, 1940],
Result = lists:zip3(First, Last, Years),
Result = lists:zip3(First, Last, Years),
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
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();
}
}
}
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();
}
}
}
clojure
(def suites ["H" "D" "C" "S"])
(def faces [2 3 4 5 6 7 8 9 10 "J" "Q" "K" "A"])
(defn listCards [] (for [s suites f faces] [f s]))
(some (partial = ["A" "H"]) (listCards))
; -> true
(count (listCards))
; -> 52
(def faces [2 3 4 5 6 7 8 9 10 "J" "Q" "K" "A"])
(defn listCards [] (for [s suites f faces] [f s]))
(some (partial = ["A" "H"]) (listCards))
; -> true
(count (listCards))
; -> 52
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]),
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]),
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).
52 = length(Deck2),
true = lists:member({h, 'A'}, Deck2).
Perform an operation on every item of a list
Perform an operation on every item of a list, e.g.
for the list
the list of sizes of the strings, 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 );
}
}
public class OperationOnEach {
public static void Main() {
var list = new List<string>() { "ox", "cat", "deer", "whale" };
list.ForEach( System.Console.WriteLine );
}
}
clojure
(map count ["ox" "cat" "deer" "whale"])
erlang
lists:map(fun (X) ->length(X) end, List).
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.
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)
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) );
}
}
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) );
}
}
clojure
(def jumble [3 "Bill" 5.7 '("A" "B" "C")]) ; int, string, float, list
(defn numberNonNumberSorter [jumbledList]
(if (empty? jumbledList)
(hash-map :numbers [], :nonnumbers []) ; recursion base case - return two empty lists
(let [head (first jumbledList)] ; let <head> be the first element in the list
(let [tailresult (numberNonNumberSorter (rest jumbledList))] ; tailresult applies recursively to the remainder
(if (number? head) ; is head a number?
(hash-map
:numbers (cons head (tailresult :numbers)) ; add <head> to the numbers
:nonnumbers (tailresult :nonnumbers)) ; leave nonnumbers the same
(hash-map
:numbers (tailresult :numbers) ; leave numbers the same
:nonnumbers (cons head (tailresult :nonnumbers))) ; add <head> to nonnumbers
)
)
)
)
)
(println (numberNonNumberSorter jumble))
; -> {:nonnumbers (Bill (A B C)), :numbers (3 5.7)}
(defn numberNonNumberSorter [jumbledList]
(if (empty? jumbledList)
(hash-map :numbers [], :nonnumbers []) ; recursion base case - return two empty lists
(let [head (first jumbledList)] ; let <head> be the first element in the list
(let [tailresult (numberNonNumberSorter (rest jumbledList))] ; tailresult applies recursively to the remainder
(if (number? head) ; is head a number?
(hash-map
:numbers (cons head (tailresult :numbers)) ; add <head> to the numbers
:nonnumbers (tailresult :nonnumbers)) ; leave nonnumbers the same
(hash-map
:numbers (tailresult :numbers) ; leave numbers the same
:nonnumbers (cons head (tailresult :nonnumbers))) ; add <head> to nonnumbers
)
)
)
)
)
(println (numberNonNumberSorter jumble))
; -> {:nonnumbers (Bill (A B C)), :numbers (3 5.7)}
(group-by number? ["hello" 42 3.14 (Date.)])
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.
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)
{Numbers, NonNumbers} = lists:partition(fun(E) -> is_number(E) end, List)
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
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)
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()
)
);
}
}
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));
.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))))))
(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)))) {}))
(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])
erlang
% Imperative Solution
Histogram = histogram(List),
Histogram = histogram(List),
% Functional (1) Solution
Histogram = histogram(List),
Histogram = histogram(List),
lists:foldl(fun(Elem, OldDict) ->
dict:update_counter(Elem, 1, OldDict)
end,
dict:new(),
[a,b,a,c,b,b])).
dict:update_counter(Elem, 1, OldDict)
end,
dict:new(),
[a,b,a,c,b,b])).
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)
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)
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
}
}
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
}
}
clojure
(loop [m {}
l ["one" "two" "three" "four" "five"]]
(if (zero? (count l))
m
(let [item (first l)
key (count item)]
(recur
(assoc m key (cons item (get m key [])))
(rest l)))))
l ["one" "two" "three" "four" "five"]]
(if (zero? (count l))
m
(let [item (first l)
key (count item)]
(recur
(assoc m key (cons item (get m key [])))
(rest l)))))
(group-by count ["one" "two" "three" "four" "five"])
erlang
% Imperative Solution
CatList = categorise(List),
CatList = categorise(List),
% Functional (1) Solution
CatList = categorise(List),
CatList = categorise(List),
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!'
print 'Hello, Bob!'
csharp
if (name == "Bob") Console.WriteLine("Hello, {0}!", name);
clojure
(def person "Bob")
(if (= person "Bob")
(println "Hello, Bob!"))
(if (= person "Bob")
(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).
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 '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");
if (age > 42)
System.Console.WriteLine("You are old");
else
System.Console.WriteLine("You are young");
clojure
(def age 41)
(if (> age 42) "You are old" "You are young")
(if (> age 42) "You are old" "You are young")
erlang
if Age > 42 -> io:format("You are old~n") ; true -> io:format("You are young~n") end.
Message = if Age > 42 -> "old" ; true -> "young" end, io:format("You are ~s~n", [Message]).
case Age > 42 of true -> io:format("You are old~n") ; false -> io:format("You are young~n") end.
case Age of _ when Age > 42 -> io:format("You are old~n") ; _ -> io:format("You are young~n") end.
Message = case Age of _ when Age > 42 -> "old" ; _ -> "young" end, io:format("You are ~s~n", [Message]).
Age > 42 andalso (begin io:format("You are old~n"), true end) orelse (begin io:format("You are young~n"), true end).
(fun (X) when X > 42 -> io:format("You are old~n"); (_) -> io:format("You are young~n") end)(Age).
(fun () when Age > 42 -> io:format("You are old~n"); () -> io:format("You are young~n") end)().
io:format("You are ~s~n", [if Age > 42 -> "old" ; true -> "young" end]).
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'
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");
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"));
clojure
(println
(condp <= age
84 "You are really ancient"
30 "You are middle aged"
"You are young"))
(condp <= age
84 "You are really ancient"
30 "You are middle aged"
"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.
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.
_ 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.
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)]
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";
}
}
{
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;
}
}
{
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;
}
}
clojure
(def n 112)
(println (str n
(let [rem (mod n 100)]
(if (and (>= rem 11) (<= rem 13))
"th"
(condp = (mod n 10)
1 "st"
2 "nd"
3 "rd"
"th")))))
(println (str n
(let [rem (mod n 100)]
(if (and (>= rem 11) (<= rem 13))
"th"
(condp = (mod n 10)
1 "st"
2 "nd"
3 "rd"
"th")))))
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])
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])
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
while x < 150:
print '%s, ' % x,
x *= 2
csharp
int x = 1;
while (x < 150)
{
x *= 2;
Console.Write("{0},", x);
}
while (x < 150)
{
x *= 2;
Console.Write("{0},", x);
}
clojure
(take-while #(< % 150) (iterate #(* 2 %) 1))
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).
Action = fun (X) -> io:format("~B,", [X]), X * 2 end,
X = 1,
while_do(Pred, Action, X).
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()))
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);
int roll;
do
{
roll = die.Next(1, 6);
Console.Write(roll);
if (roll < 6) Console.Write(",");
}
while (roll != 6);
clojure
(loop [r (rand-int 6)]
(if (= r 5)
nil
(do
(println r)
(recur (rand-int 6)))))
(if (= r 5)
nil
(do
(println r)
(recur (rand-int 6)))))
erlang
Pred = fun (DiceRoll) -> DiceRoll =/= 6 end,
Action = fun (DiceRoll) -> io:format("~B,", [DiceRoll]), dice_roll() end,
do_while(Pred, Action, dice_roll()).
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).
-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).
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"
print "Hello"
csharp
string text = "Hello";
for (int i = 0; i < 5; i++)
{
Console.Write(text);
}
for (int i = 0; i < 5; i++)
{
Console.Write(text);
}
clojure
(dotimes [_ 5]
(print "Hello"))
(print "Hello"))
erlang
dotimes(5, fun () -> io:format("Hello") end).
lists:foreach(fun (_) -> io:format("Hello") end, lists:seq(1, 5)).
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!");
{
Console.Write("{0} .. ", i);
}
Console.WriteLine("Liftoff!");
clojure
(dotimes [i 10]
(print (str (- 10 i) " .. ")))
(println "Liftoff!")
(print (str (- 10 i) " .. ")))
(println "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").
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");
clojure
(slurp "/tmp/foobar")
erlang
Text = readfile("Solution607.erl"),
Text = readfile("Solution608.erl"),
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
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())
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);
}
// 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);
}
clojure
(defn read-line-by-line [fn]
(reduce str (map (partial format "%d> %s\n")
(iterate inc 1)
(read-lines fn))))
(reduce str (map (partial format "%d> %s\n")
(iterate inc 1)
(read-lines fn))))
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).
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).
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).
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");
clojure
(with-out-writer "output.txt" (println "Hello file!"))
erlang
Line = "This line overwites file contents!\n",
{ok, IODevice} = file:open("test.txt", [write]), file:write(IODevice, Line), file:close(IODevice).
{ok, IODevice} = file:open("test.txt", [write]), file:write(IODevice, Line), file:close(IODevice).
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");
clojure
(with-out-append-writer "output.txt" (println "This is appended to the file"))
erlang
Line = "This line appended to file!\n",
{ok, IODevice} = file:open("test.txt", [append]), file:write(IODevice, Line), file:close(IODevice).
{ok, IODevice} = file:open("test.txt", [append]), file:write(IODevice, Line), file:close(IODevice).
Process each file in a directory
python
import os
results = (process(f) for f in os.listdir(".") if os.path.isfile(f))
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);
clojure
; (defn process-file [f] "process one file" body...)
(map process-file (.listFiles (File. ".")))
(map process-file (.listFiles (File. ".")))
erlang
% File basenames only - many tasks require absolute paths to work
lists:foreach(fun (FileOrDirPath) -> Worker(FileOrDirPath) end, file:list_dir(Directory)).
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)).
lists:foreach(fun (FileOrDirPath) -> Worker(FileOrDirPath) end, list_dir_path(Directory)).
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")
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.
// 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"))
(parse "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")),
LocalDateTime = erlang:universaltime_to_localtime(parse_to_datetime("2008-05-06 13:29:34")),
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.
If you can also do this without creating a Date object you can show that too.
python
from datetime import datetime
print datetime.utcnow()
print datetime.utcnow()
csharp
// Creating a variable first:
DateTime now = DateTime.Now;
Console.WriteLine(now);
// Without creating a variable:
Console.WriteLine(DateTime.Now);
DateTime now = DateTime.Now;
Console.WriteLine(now);
// Without creating a variable:
Console.WriteLine(DateTime.Now);
clojure
(import 'java.util.Date)
(println (str (Date.)))
(println (str (Date.)))
erlang
io:format("~p~n", [calendar:local_time()])
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()
""" 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();
}
}
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"))
(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"))
{:whom whom})
(defn greet [g]
(println (str "Hello, " (:whom g))))
(greet (greeter "world"))
erlang
Greeter = make_greeter("world!"),
Greeter(greet).
Greeter(greet).
Process an XML document
Given the XML Document:
<shopping>
<item name=
<item name=
</shopping>
Print out the total cost of the items, e.g. $14.50
<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
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);
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);
clojure
(println (format "Total cost of items are $%#.2f"
(->> (xml-seq (parse *xml-input-stream*))
(filter #(= :item (:tag %))) ; Remove all but the item tags
(map :attrs) ; Keep the attributes
(map (fn [e] (str "(* " (:quantity e) " " (:price e) ")"))) ; Get the total price as a sexp
(map read-string) ; "(* quantity price)" -> (* quantity price)
(map eval) ; (* quantity price) -> quantity*price
(apply +)))) ; Sum all elements
(->> (xml-seq (parse *xml-input-stream*))
(filter #(= :item (:tag %))) ; Remove all but the item tags
(map :attrs) ; Keep the attributes
(map (fn [e] (str "(* " (:quantity e) " " (:price e) ")"))) ; Get the total price as a sexp
(map read-string) ; "(* quantity price)" -> (* quantity price)
(map eval) ; (* quantity price) -> quantity*price
(apply +)))) ; Sum all elements
erlang
-include_lib("xmerl/include/xmerl.hrl").
-export([get_total/1]).
get_total(ShoppingList) ->
{XmlElt, _} = xmerl_scan:string(ShoppingList),
Items = xmerl_xpath:string("/shopping/item", XmlElt),
Total = lists:foldl(fun(Item, Tot) ->
[#xmlAttribute{value = PriceString}] = xmerl_xpath:string("/item/@price", Item),
{Price, _} = string:to_float(PriceString),
[#xmlAttribute{value = QuantityString}] = xmerl_xpath:string("/item/@quantity", Item),
{Quantity, _} = string:to_integer(QuantityString),
Tot + Price*Quantity
end,
0, Items),
io:format("$~.2f~n", [Total]).
-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]).
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=
<item name=
</shopping>
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()
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)
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>");
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>");
clojure
(defn list->xml-item [lst]
(let [[name quantity price] (map str lst)]
{:tag :item
:attrs {:name name
:quantity quantity
:price price}}))
(defn cvs->xml [r]
(->> (map #(read-string (str "(" % ")")) (line-seq r))
(map list->xml-item)
(assoc {:tag :shopping} :content)
(emit)
(with-out-str)))
(println (cvs->xml *cvs-reader*))
(let [[name quantity price] (map str lst)]
{:tag :item
:attrs {:name name
:quantity quantity
:price price}}))
(defn cvs->xml [r]
(->> (map #(read-string (str "(" % ")")) (line-seq r))
(map list->xml-item)
(assoc {:tag :shopping} :content)
(emit)
(with-out-str)))
(println (cvs->xml *cvs-reader*))
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).
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).
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)
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)
print gcd(8, 12)
csharp
public static int gcd(int a, int b)
{
if (b == 0)
return a;
else
return gcd(b, a % b);
}
{
if (b == 0)
return a;
else
return gcd(b, a % b);
}
clojure
(defn gcd [a b]
(if (zero? b)
a
(recur b (mod b a))))
(if (zero? b)
a
(recur b (mod b a))))
erlang
-module(gcd).
-export([gcd/2]).
gcd(A, 0) -> A;
gcd(A, B) -> gcd(B, A rem B).
-export([gcd/2]).
gcd(A, 0) -> A;
gcd(A, B) -> gcd(B, A rem B).
