415. Add Strings

Description

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

add-strings.py

class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        num1 = list(num1)
        num2 = list(num2)
        res = ""
        carry = 0

        def val(x):
            return ord(x) - ord('0')

        while num1 or num2 or carry:
            if num1:
                carry += val(num1.pop())
            if num2:
                carry += val(num2.pop())

            res += str(carry % 10)
            carry //= 10

        return res[::-1]