using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main(string[] args)

    {

        var permutations = Permutations<int>(new List<int> { 1, 2, 3 });

        foreach(var perm in permutations)

        {

            Console.WriteLine(string.Join(",", perm.Select(p=>p.ToString()).ToArray()));

        }

    }

    public static ICollection<ICollection<T>> Permutations<T>(ICollection<T> list) {

        var result = new List<ICollection<T>>();

        if (list.Count == 1) { // If only one possible permutation

            result.Add(list); // Add it and return it

            return result;

        }

        foreach (var element in list) { // For each element in that list

            var remainingList = new List<T>(list);

            remainingList.Remove(element); // Get a list containing everything except of chosen element

            foreach (var permutation in Permutations<T>(remainingList)) { // Get all possible sub-permutations

                permutation.Add(element); // Add that element

                result.Add(permutation);

            }

        }

        return result;

    }

}