[leetcode]: 191. Number of 1 Bits

1.题目

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.

给一个非负整数，求其二进制表示中一共有多少个1.

2.分析

3种方法：

1) n&1,n>>1 此方法只适用于非负整数的情况。如果出现负数，会死循环

2)m=1,n&m,m<<1 对m进行移位来检测每一位是否为1

3)n=n&(n-1) 每次把最低位的1置为0

3.代码

class Solution {
public:
//方法2
int hammingWeight_2(uint32_t n) {
int count=0;
int flag=1;
while(flag){
if(flag&n)
++count;
flag=flag<<1;
}
return count;
}
//方法3
int hammingWeight_3(uint32_t n) {
int count=0;
while(n){
n=n&(n-1);
++count;
}
return count;
}
};