【leetcode】【Medium】【338. Counting Bits】【规律】

注意边界及特殊情况

problem link:https://leetcode.com/problems/counting-bits/

code1(java 3ms):

public class Solution {
    public int[] countBits(int num) {
        if(num==0){
            return new int[1];
        }
        
        int[] res = new int[num + 1];
		res[1] = 1;

		int pow = 2;
		for (int i = 2; i <= num;) {
			for (int j = 0; j < pow && i <= num; j++) {
				res[i] = 1 + res[i - pow];
				i++;
			}
			pow*=2;
		}

		return res;
    }
}

discuss solution(java 2ms):

public int[] countBits(int num) {
    int[] f = new int[num + 1];
    for (int i=1; i<=num; i++) f[i] = f[i >> 1] + (i & 1);
    return f;
}