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.

向左移位就是在低位补0，向右移位就是在高位补0，按位与1作比较。

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