Number of 1 Bits问题及解法

问题描述：

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

示例：

the 32-bit integer ’11' has binary representation 

00000000000000000000000000001011

, so the function should return 3.

问题分析：

可根据向右移位与1按位与操作，可得‘1’的数目。

还有一种更高效的方式 ： n = n &( n -1 )

过程详见代码：

按位与

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

更高效方式：
int hammingWeight(uint32_t n) {
int count = 0;

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

return count;
}