Leetcode: Multiply Strings

Question

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

Hide Tags Math String
Hide Similar Problems (M) Add Two Numbers (E) Plus One (E) Add Binary

Solution

Get idea from here1, here2

class Solution(object):
    def multiply(self, num1, num2):
        """ :type num1: str :type num2: str :rtype: str """

        if len(num1)==0 or len(num2)==0 or num1=='0' or num2=='0':
            return '0'

        num1, num2 = list(num1), list(num2)
        num1.reverse()
        num2.reverse()

        res = [0]*(len(num1)+len(num2))
        for ind1 in range(len(num1)):
            a = ord(num1[ind1]) - ord('0')
            for ind2 in range(len(num2)):
                b = ord(num2[ind2]) - ord('0')
                res[ind1+ind2] += a*b

        ress = []
        carry = 0
        for ind in range(len(res)):
            digit = res[ind]%10
            ress = [(digit+carry)%10] + ress
            carry = res[ind]/10 + (digit+carry)/10


        if len(ress)>0 and ress[0]==0:
            ress = ress[1:]

        ress = [str(elem) for elem in ress]
        ress = ''.join(ress)

        return ress