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;
}