powerSet.java

    private static Set<Set<Integer>> calculatePowerSet(Set<Integer> list) {
        int size = list.size();
        Set<Set<Integer>> powerSet = new HashSet<>();
        powerSet.add(Collections.EMPTY_SET);
        if (size == 0) {
            return powerSet; 
        }
        Integer[] elems = list.toArray(new Integer[size]);
        int end = (int) Math.pow(2, size) - 1;
        for (int i=1; i<= end; i++) {
            boolean[] bits = calculateBits(i);
            Set<Integer> setElems = new HashSet<>();
            for(int j = 0; j < size; j++ ) {
                if(bits[j]) {
                    setElems.add(elems[j]);
                }
            }
            powerSet.add(setElems);
        }
        return powerSet;
    }

    private static boolean[] calculateBits(int number) {
        boolean[] bits = new boolean[32];
        for (int i = 31; i >= 0; i--) {
            bits[i] = (number & (1 << i)) != 0;
        }
        return  bits;
    }