using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Premutations(int[] array)

    {

        premutations(array, 0);

    }

​

    // this saves memory

    private static void premutations(int[] array, int start)

    {

        if (start >= array.Length)

        {

            Console.WriteLine(string.Join(",", array));

            return;

        }

​

        for (int i = start; i < array.Length; i++)

        {

            swap(i, start, array);

            premutations(array, start + 1);

            swap(i, start, array);

        }

    }

​

    private static void swap(int idx1, int idx2, int[] array)

    {

        int temp = array[idx1];

        array[idx1] = array[idx2];

        array[idx2] = temp;

    }

​

    private static void premutations(List<int> array, List<int> slate)

    {

        if (array.Count == 0)

        {

            Console.WriteLine(string.Join(",", slate));

            return;

        }

​

        for (int i = 0; i < array.Count; i++)

        {

            List<int> copy = new List<int>(array);

            copy.RemoveAt(i);

            slate.Add(array[i]);

            premutations(copy, slate);

            slate.RemoveAt(slate.Count - 1);

        }

    }

​

    public static void Main()

    {

        Premutations(new int[]{1, 2, 3});

    }

}