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public class Solution {
    public int[] countBits(int num) {
        int[] res = new int[num + 1];
        //res[0] = 0;
        for (int i = 1; i <= num; i++) {
            res[i] = res[i & (i - 1) ] + 1;
        }
        return res;
    }
}

public class Solution {
    public int[] countBits(int num) {
        int[] res = new int[num + 1];
        //res[0] = 0;
        for (int i = 1; i <= num; i++) {
            res[i] = res[i >> 1 ] + (1 & i);
        }
        return res;
    }
}