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.

判断一个数的二进制有几个1

C++(3ms):

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int res = 0 ;
        while(n){
            n = n&(n-1) ;
            res++ ;
        }
        return res ;
    }
};

java(3ms):

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