using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        IEnumerable<int[]> actual = Perm<int>.GetPermutations(Enumerable.Range(1,3).ToArray()).ToList();

        Console.WriteLine(actual.Count() + " Permutations found:");

        foreach(int[] permutation in actual)

            Console.WriteLine(String.Join(", ", permutation));

        IEnumerable<string[]> actual2 = Perm<string>.GetPermutations(new []{"A","B","C"}).ToList();

        Console.WriteLine(actual2.Count() + " Permutations found:");

        foreach(string[] permutation in actual2)

            Console.WriteLine(String.Join(", ", permutation));

    }

}

​

public static class Perm<T>

{

    public static IEnumerable<T[]> GetPermutations(T[] items)

    {

        return GeneratePermutations(items, 0, items.Length - 1).ToList();

    }

​

    // http://stackoverflow.com/a/756083/4035

    private static IEnumerable<T[]> GeneratePermutations(T[] permutationList, int startCount, int permutationCount)

    {

        if (startCount == permutationCount)

        {

            yield return permutationList;

        }

        else

        {

            for (int i = startCount; i <= permutationCount; i++)

            {

                Swap(permutationList, startCount, i);

                IEnumerable<T[]> perms = GeneratePermutations((T[])permutationList.Clone(), startCount + 1, permutationCount).ToList();

                foreach(T[] perm in perms)

                    yield return perm;

                Swap(permutationList, startCount, i);

            }

​

        }

    }

​

    // http://stackoverflow.com/a/2094316/4035

    public static void Swap(T[] list, int index1, int index2)

    {

        T tmp = list[index1];

        list[index1] = list[index2];

        list[index2] = tmp;

    }

}