leetcode------Number of 1 Bits

标题：	Number of 1 Bits
通过率：	40.0%
难度：	简单

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.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

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本题就是数给的十进制数的二进制数有几个1。

最基本的做法就是32位扫描一遍进行查，我查看网页后找到一种简单的方法，减1法，每次把二进制减一，一直减到0为止，

n=n&(n-1)；

具体代码如下：

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