lc面试准备:Number of 1 Bits

1 题目

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.

接口

public int hammingWeight(int n);

2 思路

统计出一个数用二进制表示的时候，里面'1'的个数。

和Reverse Bits思路一样，位运算。

复杂度

Time: O(n)  Space: O(1)

3 代码

     public int hammingWeight(int n) {
         int res = 0;
         for (int i = 0; i < 32; i++) {
             final int bit = (n >> i) & 1;
             res += bit;
         }
         return res;
     }

4 总结

和Reverse Bits思路一样。

5 参考

1. leetcode
2. Leetcode: Number of 1 Bits