LC1009 Complement of Base 10 Integer

class Solution:
    def bitwiseComplement(self, N: int) -> int:
        # time O(lgN) space O(1)
        # N + complement(N) = 11111 = X
        x  = 1 
        while N > x: 
            x = x *2 +1
        return x - N

class Solution:
    def bitwiseComplement(self, N: int) -> int:
        # N ^ bitwisecomplement(N) = 1111 = X
        #  ===>  N ^ X = bitwisecomplement(N)
        # time O(lgN) space O(1)
        x = 1
        while N> x:
            x = x*2 +1
        return N^x