Generating power set recursively without any loops

Question

How do you write a recursive method PowerSet(String input) that prints out all possible combinations of a string that is passed to it?

For example: PowerSet(\"abc\")

Answer 1

Well if you don't have loops, emulate one with recursion, using iterators this is acutally quite simple.

    public final Set> powerSet(Set set) {
        Set> powerSet = new HashSet<>();
        powerSet(set, powerSet, set.iterator());
        return powerSet;
    }
    public final void powerSet(Set set, Set> powerSet, Iterator iterator) {
        if(iterator.hasNext()) {
            Integer exlude = iterator.next();
            Set powThis = new HashSet();
            powThis.addAll(set);
            powThis.remove(exlude);
            powerSet.add(powThis);
            powerSet(powThis, powerSet, powThis.iterator());
            powerSet(set, powerSet, iterator);
        }
    }
//usage
        Set set = new HashSet<>();
        set.add(1);
        set.add(2);
        set.add(3);
        set.add(4);
        log.error(powerSet(set).toString());