Add binary

We will start from the end character of each number, add that and if the sum is more than 2, we take the reminder to the next digit, and add the last digit to our result. We will continue the process until the beginning of both number.

class Solution:
    def addBinary(self, a: str, b: str) -> str:
        rem, res = 0, ''
        a, b = list(a), list(b)

        while a or b:
            if a: rem += int(a.pop())
            if b: rem += int(b.pop())
            res = str(rem%2) + res
            rem //= 2

        return str(rem)+res if rem == 1 else res

Time Complexity: O(max(n, m))
Space Complexity: O(1)