algorithms/string/multiply_strings.py at master · KECB/algorithms · GitHub

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"""

Given two non-negative integers num1 and num2 represented as strings,

return the product of num1 and num2.

Note:

The length of both num1 and num2 is < 110.

Both num1 and num2 contains only digits 0-9.

Both num1 and num2 does not contain any leading zero.

You must not use any built-in BigInteger library or convert

the inputs to integer directly.

"""

def multiply(num1:"str", num2:"str")->"str":

carry = 1

interm = []

zero = ord('0')

i_pos = 1

for i in reversed(num1):

j_pos = 1

add = 0

for j in reversed(num2):

mult = (ord(i)-zero) * (ord(j)-zero) * j_pos * i_pos

j_pos *= 10

add += mult

i_pos *= 10

interm.append(add)

return str(sum(interm))

if __name__ == "__main__":

print(multiply("1", "23"))

print(multiply("23", "23"))

print(multiply("100", "23"))

print(multiply("100", "10000"))

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