43. Multiply Strings

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

Example 1:

Input: num1 = "2", num2 = "3"
Output: "6"

Example 2:

Input: num1 = "123", num2 = "456"
Output: "56088"

Note:

1. The length of both num1 and num2 is < 110.
2. Both num1 and num2 contain only digits 0-9.
3. Both num1 and num2 do not contain any leading zero, except the number 0 itself.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

Code:

class Solution(object):
    def multiply(self, num1, num2):
        """
        :type num1: str
        :type num2: str
        :rtype: str
        """
        result = 0
        for i in range(len(num1)-1, -1, -1):
            for j in range(len(num2)-1, -1, -1):
                int1 = ord(num1[i]) - ord('0')
                int2 = ord(num2[j]) - ord('0')
                result += (int1 * 10 ** (len(num1)-1 - i)) * (int2 * 10 ** (len(num2)-1-j))
        return str(result)