Add Strings

Solution

Let $m$ be the length of num1, and $n$ be the length of num2.

Math

Could also have res as a list of integers instead.

Complexity

time: $O(\max (m, n))$
space: $O(\max (m, n))$

def addStrings(self, num1: str, num2: str) -> str:

    i, j = len(num1)-1, len(num2)-1
    res = ''
    carry = 0

    while i >= 0 or j >= 0:
        a = ord(num1[i]) - ord('0') if i >= 0 else 0
        b = ord(num2[j]) - ord('0') if j >= 0 else 0
        carry, sum = divmod(a + b + carry, 10)
        res += str(sum)
        i -= 1
        j -= 1

    if carry:
        res += str(carry)

    return res[::-1]