【leetcode刷题笔记】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.

题解：利用位运算的知识，n&(n-1)的结果会出去n的最后一位1.比如n=11=1011，n-1=10=1010,那么n&(n-1)=1010,最后一位1就没有了。设置一个循环，每次赋值n=n&(n-1)。n为0的时候统计循环的次数就知道n的二进制里面有多少个1了。

Java代码：

 public class Solution {
     // you need to treat n as an unsigned value
     public int hammingWeight(int n) {
         int sum = 0;
         while(n != 0){
             sum ++;
             n = n&(n-1);
         }
         return sum;
     }
 }