Solution
from typing import List
class Solution:
def multiply(self, num1: str, num2: str) -> str:
if num1 == "0" or num2 == "0":
return "0"
m, n = len(num1), len(num2)
arr = [0] * (m + n)
for i in range(m - 1, -1, -1):
a = int(num1[i])
for j in range(n - 1, -1, -1):
b = int(num2[j])
arr[i + j + 1] += a * b
for i in range(m + n - 1, 0, -1):
arr[i - 1] += arr[i] // 10
arr[i] %= 10
i = 0 if arr[0] else 1
return "".join(str(x) for x in arr[i:])
if __name__ == "__main__":
sol = Solution()
print(sol.multiply("2", "3")) # "6"
print(sol.multiply("123", "456")) # "56088"
print(sol.multiply("0", "12345")) # "0"