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.
python代码：
class Solution:
# @param n, an integer
# @return an integer
def hammingWeight(self, n):
count=0
if n==0: #输入为0时，输出为0
return count
count+=1
while n&n-1: #利用位运算，获得1的个数
n=n&n-1
count=count+1
return count