核心：n&(n-1)将1消掉，负数的表示：n&0xffffffff。

# -*- coding:utf-8 -*-
class Solution:
    def NumberOf1(self, n):
        res = 0
        n = n & 0xffffffff
        while n!=0:
            n = n &(n-1)
            res += 1
        return res