[leetcode 191]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.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

 

2 分析

开始想的是转化为bit数组再一个一个查是否是1，后来发现java系统函数的bitCount，发现满足条件。。

另外我看别人的方法是循环32次，每次与1相与并右移动一位。想法蛮好的。

3 代码

    public int hammingWeight(int n){

        return Integer.bitCount(n);
        
    }

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