using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var flags = GetPermutations(new[] {"a", "b", "c", "d", "e"})

            .Select(a => string.Join(",", a.ToArray()))

            .ToList();

        Console.WriteLine(string.Join("\n", flags));

    }

​

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

    {

        return GetPermutations(items, 0)

            .OrderBy(x => x.Count());

    }

    private static IEnumerable<IEnumerable<T>> GetPermutations<T>(T[] items, int start)

    {

        for (var pos = start; pos < items.Length; pos++)

        {

            yield return new[] { items[pos] };

            foreach (var permutations in GetPermutations(items, pos + 1))

            {

                yield return new[] { items[pos] }.Concat(permutations);

            }

        }

    }

}