leetcode刷题-43字符串相乘

class Solution:
    def multiply(self, num1: str, num2: str) -> str:

        def mul(string):
            product = 0
            for i in string:
                product = product*10
                product += int(i)
            return product

        a = mul(num1)
        b = mul(num2)
        result = a * b
        return str(result)