Tricky Google interview question

Question

A friend of mine is interviewing for a job. One of the interview questions got me thinking, just wanted some feedback.

There are 2 non-negative integers: i and j. Gi

Answer 1

If we are allowed to use java Collection then we can have these number in O(n^2)

public static void main(String[] args) throws Exception {
    int powerLimit = 7;  
     int first = 2;
     int second = 5;
    SortedSet set = new TreeSet();

    for (int i = 0; i < powerLimit; i++) {
        for (int j = 0; j < powerLimit; j++) {
            Integer x = (int) (Math.pow(first, i) * Math.pow(second, j));
            set.add(x);
        }
    }

    set=set.headSet((int)Math.pow(first, powerLimit));

    for (int p : set)
        System.out.println(p);
}

Here powerLimit has to be initialised very carefully !! Depending upon how many numbers you want.