LeetCode 338. Counting Bits

public class Solution {    public int[] countBits(int num) {        int[] bits = new int[num + 1];        int level = 0;        bits[0] = 0;        for (int i = 1; i <= num; i++) {        int n = 1 << level;        if (i == n) bits[i] = 1;        else if (i < n + n / 2) bits[i] = bits[i - n / 2];        else bits[i] = bits[i - n / 2] + 1;        if (i + 1 == n * 2) level++;        }        return bits;    }}