Lists permutations (unknown number) [duplicate]

Answer 1

Non-recursive solution, works on any IEnumerables (not just lists) without solidifying them:

public static IEnumerable> Permutations(
    this IEnumerable> source)
{
    // Check source non-null, non-empty?

    var enumerables = source.ToArray();
    Stack> fe = new Stack>();
    fe.Push(enumerables[0].GetEnumerator());

    while (fe.Count > 0)
    {
        if (fe.Peek().MoveNext())
        {
            if (fe.Count == enumerables.Length)
                yield return new Stack(fe.Select(e => e.Current));
            else
                fe.Push(enumerables[fe.Count].GetEnumerator());
        }
        else
        {
            fe.Pop().Dispose();
        }
    }
}