class Solution:
def addStrings(self, num1: str, num2: str) -> str:
num1 = list(num1[::-1])
num2 = list(num2[::-1])
if len(num1) > len(num2):
num1, num2 = num2, num1
up = 0
ans = []
for i in range(len(num1)):
n1, n2 = int(num1[i]), int(num2[i])
tmp = up + n1 + n2
up = tmp // 10
ans.append(str(tmp % 10))
for i in range(len(num1), len(num2)):
n2 = int(num2[i])
tmp = up + n2
up = tmp // 10
ans.append(str(tmp % 10))
if up:
ans.append('1')
return ''.join(ans[::-1])