LeetCode: Counting Bits

f[i] = f[i/2] + i%2;

public class Solution {
    public int[] countBits(int num) {
        int[] ans = new int[num+1];
        for (int i = 0; i < ans.length; i++) {
            ans[i] = ans[i / 2] + i % 2;
        }
        return ans;
    }
}