【leetcode】-191. Number of 1 Bits 数字二进制表示1的个数

题目

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

Example 1:

Input: 00000000000000000000000000001011
Output: 3
Explanation: The input binary string 00000000000000000000000000001011 has a total of three ‘1’ bits.
Example 2:

Input: 00000000000000000000000010000000
Output: 1
Explanation: The input binary string 00000000000000000000000010000000 has a total of one ‘1’ bit.
Example 3:

Input: 11111111111111111111111111111101
Output: 31
Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one ‘1’ bits.

位运算

n&(n-1)可用于消除二进制当中的最后一个1。

所以这题求1的个数，可以用一个循环来消除最后一个1，直到数为0为止。

Java

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;
    }
}