415. Add Strings-字符串相加

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

Note:

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

Solution in python:

class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        def convert(s):
            base = 1
            result = 0
            for i in range(len(s)-1, -1, -1):
                result += base* int(s[i])
                base *= 10
            return result

        def printout(n):
            result = ""
            if n == 0:
                return "0"
            while n > 0:
                r = n % 10
                n //= 10
                result = str(r) + result
            return result

        return printout(convert(num1)+convert(num2))