Permutations of Sequences in Swift

permutations.swift

func permutations<Sequence: SequenceType>(items: Sequence) -> [[Sequence.Generator.Element]] {
	return items.reduce([[]]) { (perms, item) in
		return perms.flatMap { perm in
			return (0 ... perm.count).map { i in
				var copy = perm
				copy.insert(item, atIndex: i)
				return copy
			}
		}
	}
}