Number of 1 Bits

Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the Hamming weight).

For example, the 32-bit integer ’11' has binary representation 00000000000000000000000000001011, so the function should return 3.

不敢相信我的眼睛了，居然这么简单的题目。

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int cnt=0;
        while(n) {
            if(n%2)
                cnt++;
            n /= 2;
        }
        return cnt; 
    }
};

最近在书上看到一种复杂度更少的解法O(M),M为1的个数：

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int cnt=0;
        while(n) {
            n &= (n-1);
            ++cnt;
        }
        return cnt; 
    }
};