README.md

415. Add Strings

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

Note:

1. The length of both num1 and num2 is < 5100.
2. Both num1 and num2 contains only digits 0-9.
3. Both num1 and num2 does not contain any leading zero.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

Solutions (Python)

1. Straight Forward

class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        sum = ""
        i, j = len(num1) - 1, len(num2) - 1
        carry = 0

        while i >= 0 or j >= 0:
            carry += ord(num1[i]) - 48 if i >= 0 else 0
            carry += ord(num2[j]) - 48 if j >= 0 else 0

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

            i -= 1
            j -= 1

        return '1' * carry + sum[::-1]