Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the ).

For example, the 32-bit integer ’11' has binary representation 00000000000000000000000000001011, so the function should return 3.

分析：题意为计算32位整型数2进制表示中1的个数。

方法还是非常多的，也很好理解：

1、利用2进制的数学特点来

class Solution {public:    int hammingWeight(uint32_t n) {        int count=0;        while(n){        if(n%2==1) count++;        n=n/2;        }        return count;    }};

2、将每一位分别和1做与运算，计算不为0的个数即可

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

3、每次n&(n-1)可以将n里面的值为1的位数减少一位

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