Finding permutations in strings

In C++ the Standard Template Library provides us with std::next_permutation to easily implement this. [code language="cpp"] #include <iostream> #include <algorithm> #include <iterator> #include <string.h> int main() { char str[] = "abcd"; const size_t len = strlen( str ); do { std::copy( str, str + len, std::ostream_iterator<char>( std::cout ) ); std::cout << std::endl; } while ( std::next_permutation( str, str + len ) ); return 0; } [/code] Giving the following output: permutations1 The C# / .NET framework does not have an equivalent for std::next_permutation, but is straightforward enough to implement: This following StackOverflow post gives an excellent C# implementation of next_permutation, which I've used here: https://stackoverflow.com/questions/2390954/how-would-you-calculate-all-possible-permutations-of-0-through-n-iteratively/12768718#12768718 [code language="csharp"] using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace permutations_cs { class Program { static bool next_permutation<T>(IList<T> a) where T : IComparable { if (a.Count < 2) return false; var k = a.Count - 2; while (k >= 0 && a[k].CompareTo(a[k + 1]) >= 0) k--; if (k < 0) return false; var l = a.Count - 1; while (l > k && a[l].CompareTo(a[k]) <= 0) l--; var tmp = a[k]; a[k] = a[l]; a[l] = tmp; var i = k + 1; var j = a.Count - 1; while (i < j) { tmp = a[i]; a[i] = a[j]; a[j] = tmp; i++; j--; } return true; } static void Main(string[] args) { char[] str = { 'a', 'b', 'c', 'd' }; do { Console.WriteLine(str); } while ( next_permutation( str ) ); } } } [/code] Giving an identical output: permutations2

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