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