Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Note: You must not use any built-in BigInteger library or convert the inputs to integer directly.【The sadest things which I can found the fastest soultion in leetcode break this rule.】

• https://leetcode.com/problems/multiply-strings/

Solution

• submit code

class Solution:
    def multiply(self, num1: str, num2: str) -> str:
        #return str(eval(num1 + "*" + num2))

        # base case
        if num1 == "0" or num2 == "0":
            return "0"

        ret = [0] * (len(num1) + len(num2))

        i = len(num1) - 1
        while i >= 0:
            j = len(num2) - 1
            while j >= 0:
                mul = int(eval(num1[i] + "*" + num2[j]))
                p1 = i + j
                p2 = i + j + 1
                sum = int(ret[p2]) + mul

                ret[p2] = sum % 10
                ret[p1] = int(ret[p1]) + int(sum / 10)
                j -= 1
            i -= 1

        # remove the leading 0
        while ret[0] == 0:
            ret = ret[1:]

        res = ""
        for i in ret:
            res += str(i)

        return res

• full code

class Solution:
    def multiply(self, num1, num2):
        #return str(eval(num1 + "*" + num2))

        # base case
        if num1 == "0" or num2 == "0":
            return "0"

        ret = [0] * (len(num1) + len(num2))

        i = len(num1) - 1
        while i >= 0:
            j = len(num2) - 1
            while j >= 0:
                mul = int(eval(num1[i] + "*" + num2[j]))
                p1 = i + j
                p2 = i + j + 1
                sum = int(ret[p2]) + mul

                ret[p2] = sum % 10
                ret[p1] = int(ret[p1]) + int(sum / 10)
                j -= 1
            i -= 1

        # remove the leading 0
        while ret[0] == 0:
            ret = ret[1:]

        res = ""
        for i in ret:
            res += str(i)

        return res


S = Solution()
print(S.multiply("12", "456"))