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.

有三种方法计算1的个数，可以参看我的其他随笔

1 class Solution {
2 public:
3     int hammingWeight(uint32_t n) {
4          bitset<64> bs(n);
5           return bs.count();
6           
7     }
8 };

191. Number of 1 Bits（LeetCode）