Add 2 Strings

class Solution:
    def add_two_lists(self, list1: list[str], list2: list[str]) -> str:
        from collections import deque
        answers = deque([])
        remainder = 0

        i1 = len(list1) - 1; i2 = len(list2) - 1
        while True:
            # Base
            if i1 < 0 and i2 < 0:
                break

            num1 = int(list1[i1]) if not (i1 < 0) else 0
            num2 = int(list2[i2]) if not (i2 < 0) else 0

            total = num1 + num2 + remainder
            next_digit, remainder = total % 10, total // 10 # max total = 18
            answers.appendleft(str(next_digit))

            i1 -= 1; i2 -= 1
        if remainder > 0:
            answers.appendleft(str(remainder))

        return "".join(answers)