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

We could write the power set with or without using recursion. Here is an attempt without recursion:

public List> getPowerSet(List set) {
    List> powerSet = new ArrayList>();
    int max = 1 << set.size();
    for(int i=0; i < max; i++) {
        List subSet = getSubSet(i, set);
        powerSet.add(subSet);
    }
    return powerSet;
}

private List getSubSet(int p, List set) {
    List subSet = new ArrayList();
    int position = 0;
    for(int i=p; i > 0; i >>= 1) {
        if((i & 1) == 1) {
            subSet.add(set.get(position));
        }
        position++;
    }
    return subSet;
}