位运算，两种解法：

解法一：

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int count = 0;

        while ( n > 0 ) {
            if ( n & 1 )
                ++count;
            n >>= 1;
        }

        return count;
    }
};

解法二：

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int count = 0;

        while ( n ) {
            ++count;
            n = n & ( n - 1 );
        }

        return count;
    }
};