LeetCode-191~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.
给定一个unsigned integer数，返回bit值为1的个数

算法分析

方法一

将给定数值与1做“与”运算，即可得到结果

Java代码

public class Solution {
    // you need to treat n as an unsigned value
    public int hammingWeight(int n) {
        int count = 0;
        int mask = 1;
        for (int i = 0; i < 32; i ++) {
            if ((n & mask) != 0) {
                count ++;
            }
            mask = mask << 1;
        }
        return count;
    }
}

方法二

如图1所示，n & (n - 1)运算

Paste_Image.png

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 - 1);
        }
        return sum;
    }
}

参考

LeetCode