191. Number of 1 Bits

https://leetcode.com/problems/number-of-1-bits/

1. Use bit mask:

//4 ms    5.9 MB
class Solution {
public:
    int hammingWeight(uint32_t n) {
        int bits = 0;
        uint32_t mask = 1;
        for(int i=0; i<32; i++){
            if((n & mask) != 0){
                bits++;
            }
            mask <<= 1;
        }
        return bits;
    }
};