.NET Fiddle

CSharp · Console

/Program.cs

using System;
using System.Linq;
using System.Collections.Generic;
					
public class Program
{
	static IEnumerable<IEnumerable<T>> GetPermutations<T>(IEnumerable<T> list, int length)
	{
		if (length == 1) return list.Select(t => new T[] { t });

		return GetPermutations(list, length - 1)
			.SelectMany(t => list.Where(e => !t.Contains(e)),
						(t1, t2) => t1.Concat(new T[] { t2 }));
	}
	
	public static void Main()
	{
		char[] aakkoset = new[] {'a', 'b', 'c'};
		foreach (var permutaatio in GetPermutations(aakkoset, 3))
		{
			Console.WriteLine(string.Join(',', permutaatio));	
		}
	}
}