Add Strings

Given two non-negative integers, num1 and num2 represented as string, return the sum of num1 and num2 as a string.

You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly.

Example 1:

Input: num1 = "11", num2 = "123"
Output: "134"

Example 2:

Input: num1 = "456", num2 = "77"
Output: "533"

Example 3:

Input: num1 = "0", num2 = "0"
Output: "0"

Constraints:

• 1 <= num1.length, num2.length <= 104
• num1 and num2 consist of only digits.
• num1 and num2 don't have any leading zeros except for the zero itself.

SOLUTION:

class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        m = len(num1)
        n = len(num2)
        if m < n:
            num1 = "0" * (n - m) + num1
        else:
            num2 = "0" * (m - n) + num2
        carry = 0
        i = max(m, n) - 1
        op = ""
        while i >= 0:
            val = carry + int(num1[i]) + int(num2[i])
            op = str(val % 10) + op
            carry = val // 10
            i -= 1
        if carry > 0:
            op = "1" + op
        return op