题目: https://leetcode.com/problems/number-complement/
难度: Easy
class Solution(object):
def findComplement(self, num):
"""
:type num: int
:rtype: int
"""
i = 1 << (len(bin(num)) -2) # 因为bin函数转化成的格式是‘0bXXXX’，头两个‘0b’要减掉去
return (i - 1) ^ num
# return (i - 1) - num # 这样也可以