0415. Add Strings.md

题目

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.

我的思路

这道题要求将两个用string表示的数字相加，并且不能使用内置函数和强制转换int。因此我就将其作为字符串来进行处理，每次取两个字符串的最后一位相加，计算结果用其表示的数字的ascii码来保存，carry保存进位，每次将计算出的一位数字转换为对应的char保存进res字符串中，最后逆序输出res字符串。

class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        carry = 0
        res = ''
        i = len(num1) - 1
        j = len(num2) - 1
        while i >= 0 or j >= 0:
            if i >= 0:
                carry += ord(num1[i]) - ord("0")
                i -= 1
            if j >= 0:
                carry += ord(num2[j]) - ord("0")
                j -= 1
                
            res += chr(carry % 10 + ord("0"))
            carry = carry // 10
            
        if carry == 1:
            res += '1'
        
        return res[::-1]