Multiply two strings Python

PROGRAM TO MULTIPLY LARGE NUMBERS REPRESENTED AS STRINGS

# Multiplies str1 and str2, and prints result.

def multiply(num1, num2):

    len1 = len(num1)

    len2 = len(num2)

    if len1 == 0 or len2 == 0:

        return "0"

  

    # will keep the result number in vector

    # in reverse order

    result = [0] * (len1 + len2)

      

    # Below two indexes are used to 

    # find positions in result.

    i_n1 = 0

    i_n2 = 0

  

    # Go from right to left in num1

    for i in range(len1 - 1, -1, -1):

        carry = 0

        n1 = ord(num1[i]) - 48

  

        # To shift position to left after every

        # multiplication of a digit in num2

        i_n2 = 0

  

        # Go from right to left in num2

        for j in range(len2 - 1, -1, -1):

              

            # Take current digit of second number

            n2 = ord(num2[j]) - 48

          

            # Multiply with current digit of first number

            # and add result to previously stored result

            # at current position.

            summ = n1 * n2 + result[i_n1 + i_n2] + carry

  

            # Carry for next iteration

            carry = summ // 10

  

            # Store result

            result[i_n1 + i_n2] = summ % 10

  

            i_n2 += 1

  

            # store carry in next cell

        if (carry > 0):

            result[i_n1 + i_n2] += carry

  

            # To shift position to left after every

            # multiplication of a digit in num1.

        i_n1 += 1

          

        # print(result)

  

    # ignore '0's from the right

    i = len(result) - 1

    while (i >= 0 and result[i] == 0):

        i -= 1

  

    # If all were '0's - means either both or

    # one of num1 or num2 were '0'

    if (i == -1):

        return "0"

  

    # generate the result string

    s = ""

    while (i >= 0):

        s += chr(result[i] + 48)

        i -= 1

  

    return s

  

# Driver code

str1 = "1235421415454545454545454544"

str2 = "1714546546546545454544548544544545"

  

if((str1[0] == '-' or str2[0] == '-') and 

   (str1[0] != '-' or str2[0] != '-')):

    print("-", end = '')

  

  

if(str1[0] == '-' and str2[0] != '-'):

    str1 = str1[1:]

elif(str1[0] != '-' and str2[0] == '-'):

    str2 = str2[1:]

elif(str1[0] == '-' and str2[0] == '-'):

    str1 = str1[1:]

    str2 = str2[1:]

print(multiply(str1, str2))







OUTPUT

2118187521397235888154583183918321221520083884298838480662480

CREDITS: https://www.geeksforgeeks.org/multiply-large-numbers-represented-as-strings/