# Number of 1 Bits

### 描述​

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.

### 分析​

1. 输入值 n 可能为负数，但应视其为无符号整数，因为 Java 中实际上是没有无符号整数的
2. 使用无符号右移操作符>>>，可以忽略符号位

### 解法 1​

// Number of 1 Bits// Time Complexity: O(32), Space Complexity: O(1)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) {            count += n & 1;            n >>>= 1;        }        return count;    }}

### 解法 2​

// Number of 1 Bits// Time Complexity: O(number of 1), Space Complexity: O(1)public class Solution {    // you need to treat n as an unsigned value    public int hammingWeight(int n) {        int count = 0;        while (n != 0) {            ++count;            n &= n - 1;        }        return count;    }}