43. Multiply Strings

class Solution:
    def add(self, num1, num2):
        if not num1 or not num2:
            return num1 or num2

        if num1 == '0':
            return num2

        if num2 == '0':
            return num1

        long = num1 if len(num1) >= len(num2) else num2
        short = num1 if len(num1) < len(num2) else num2

        diff = len(long) - len(short)

        long1 = long[:diff]
        long2 = long[diff:]

        res = ''

        carry = 0
        i = len(short) - 1
        while i >= 0:
            num1 = ord(short[i]) - ord('0')
            num2 = ord(long2[i]) - ord('0')
            temp = num1 + num2 + carry
            d = chr(temp % 10 + ord('0'))
            carry = temp // 10

            res = d + res
            i = i - 1

        i = len(long1) - 1
        while i >= 0:
            num = ord(long1[i]) - ord('0')
            temp = num + carry
            d = chr(temp % 10 + ord('0'))
            carry = temp // 10

            res = d + res
            i = i - 1

        if carry:
            d = chr(carry + ord('0'))
            res = d + res

        return res


    def multiply(self, num1, num2):
        """
        :type num1: str
        :type num2: str
        :rtype: str
        """
        if num1 is '0' or num2 is '0':
            return '0'

        if not num1 or not num2:
            return '0'

        long = num1 if len(num1) >= len(num2) else num2
        short = num1 if len(num1) < len(num2) else num2

        res = ''

        zero = 0

        i = len(short) - 1
        while i >= 0:
            carry = 0

            num1 = ord(short[i]) - ord('0')

            res_t = '0' * zero

            j = len(long) - 1
            while j >= 0:
                num2 = ord(long[j]) - ord('0')
                temp = num1 * num2 + carry
                carry = temp // 10
                p = chr(temp % 10 + ord('0'))
                res_t = p + res_t

                j = j - 1

            if carry:
                p = chr(carry + ord('0'))
                res_t = p + res_t

            res = self.add(res, res_t)

            zero = zero + 1

            i = i - 1

        return res