JadenGeller

extension Array {
	var powerSet: [[Element]] {
		guard !isEmpty else { return [[]] }
		return Array(self[1...]).powerSet.flatMap { [$0, [self[0]] + $0] }
	}
}

print([1,2,3,4].powerSet) // -> [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3], [4], [1, 4], [2, 4], [1, 2, 4], [3, 4], [1, 3, 4], [2, 3, 4], [1, 2, 3, 4]]