Saved from https://leetcode.com/problems/add-strings/

lc415

class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        res = []
        len1, len2 = len(num1), len(num2)
        carry = 0
        i = 0
        while i < len1 or i < len2:
            sum = carry
            if i < len1:
                sum += int(num1[len1-1-i])
            if i < len2:
                sum += int(num2[len2-1-i])

            if sum >= 10:
                carry = 1
                sum = sum % 10
            else:
                carry = 0
            res.append(sum)
            i += 1
        if carry:
            res.append(carry)
        return ''.join(str(x) for x in res[::-1])