[LeetCode] 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.

解题思路1

每一位分别和1进行与运算，统计结果不为0的位数。

实现代码1

//Runtime:10 ms
#include <iostream>
#include "inttypes.h"
using namespace std;

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int i = 0;
        while (n)
        {
            i += n & 0x1;
            n >>= 1;
        }

        return i;
    }
};

int main()
{
    Solution s;
    cout<<s.hammingWeight(11)<<endl;
    return 0;
}

解题思路2

每次n&(n-1)可以将n里面的值为1的位数减少一位

实现代码2

//Runtime:11 ms
class Solution {
public:
    int hammingWeight(uint32_t n) {
        int i = 0;
        while (n)
        {
            n &= (n-1);
            ++i;
        }

        return i;
    }
};