题目
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.
解题思路
推展到n个数的方案，用数组存每个数的长度，每次相加所有数字的最后一位（数的长度），加完之后，长度-1，当所有长度都为0，并且没进位的时候结束
代码
class Solution:
def addStrings(self, num1: str, num2: str) -> str:
nums = [num1, num2]
n = len(nums)
l = [len(num) for num in nums]
c = 0
res = []
while any(l) or c:
for i in range(n):
if l[i]:
l[i] -= 1
c += int(nums[i][l[i]])
res.append(str(c % 10))
c //= 10
return "".join(reversed(res))
