class Solution {
public:
    int NumberOf1(int n) {
        int res = 0;
        for (int i = 0; i < 32; i ++ )
        if (n >> i & 1)
        res ++ ;

        return res;
    }
};

第二种写法(lowbiot)

class Solution {
public:
    int NumberOf1(int n) {
        int res = 0;
        while (n) n -= n & -n, res ++ ;

        return res;
    }
};