powerful_integers.java

public List<Integer> powerfulIntegers(int x, int y, int bound) {
        Set<Integer> set = new HashSet();
        for(int i=1; i<=bound; i*=x) {
            for(int j=1; i+j <= bound; j*=y) {
                set.add(i+j);
                if(y == 1) break;
            }
            if(x == 1) break;
        }
        
        return new ArrayList(set);
    }