191. 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.

求一个32位无符号整形数二进制表达中'1'的个数。

解决： n = n & (n - 1) 可以把二进制中最后一个1变成0 

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