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。

 1 class Solution {
 2 public:
 3     int hammingWeight(uint32_t n) {
 4         int cnt=0;
 5         while(n) {
 6             if(n%2)
 7                 cnt++;
 8             n /= 2;
 9         }
10         return cnt; 
11     }
12 };

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：

 1 class Solution {
 2 public:
 3     int hammingWeight(uint32_t n) {
 4         int cnt=0;
 5         while(n) {
 6             n &= (n-1);
 7             ++cnt;
 8         }
 9         return cnt; 
10     }
11 };