Number Complement⌗

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Example: Input: 5 Output: 2 Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.

My submission:

class Solution:
    def findComplement(self, num: int) -> int:
        length = len(bin(num)) - 2
        return 2 ** length - num -1

some other methods in discussions: using bitwise shift

class Solution(object):
    def findComplement(self, num):
        i = 1
        while i <= num:
            i = i << 1
        return (i - 1) ^ num

    # the core is ^, 111 ^ 101 = 010

C++ method with bitwise operators