Obtaining a powerset of a set in Java

Question

The powerset of {1, 2, 3} is:

{{}, {2}, {3}, {2, 3}, {1, 2}, {1, 3}, {1, 2, 3}, {1}}

Let\'s say I have a Set in Java:<

Answer 1

This is my approach with lambdas.

public static  Set> powerSet(T[] set) {
      return IntStream
            .range(0, (int) Math.pow(2, set.length))
            .parallel() //performance improvement
            .mapToObj(e -> IntStream.range(0, set.length).filter(i -> (e & (0b1 << i)) != 0).mapToObj(i -> set[i]).collect(Collectors.toSet()))
            .map(Function.identity())
            .collect(Collectors.toSet());
        }

Or in parallel (see parallel() comment):

Size of input set: 18

Logical processors: 8 à 3.4GHz

Performance improvement: 30%