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.

解题思路：

JAVA实现如下：

    public int hammingWeight(int n) {

		int res = 0;

		while(n!=0){

			res += n & 1;

			n >>>= 1;

		}

		return res;

    }