using System;
using System.Collections.Generic;
using System.Linq;

static class Program
{
    private static void Main(string[] args)
	{
		"foo".ToCharArray().Permutate().ForEach(Console.WriteLine);
		"abbccc".ToCharArray().Permutate().ForEach(Console.WriteLine);

		Console.Read();
	}

	public static List<string> Permutate(this IEnumerable<char> s)
	{
		return s.SelectMany(x =>
			{
				var index = Array.IndexOf(s.ToArray(), x);
				return
					s.Where((y, i) => i != index)
					 .Permutate()
					 .Select(y => new string(new[] {x}.Concat(y).ToArray()))
					 .Union(new[] {new string(new[] {x})});
			}).Distinct().Where(x => x.Length == s.Count()).ToList();
	}
}