Number of 1 Bits leetcode

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.

解法1: 把每一位都 & 1, 计算所有1的个数
解法2: 因为n & (n - 1)就可以消除掉最右边的一个1, 比如110，减去1得101，相与得100，消去了最右边的1。这样一直消除到没有, 可以计算出1得个数

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

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