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.

只需注意 n & (n - 1) 能够快速清空最后一个1

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