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"""

Project Euler Problem 4: https://projecteuler.net/problem=4

Largest palindrome product

A palindromic number reads the same both ways. The largest palindrome made

from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

References:

- https://en.wikipedia.org/wiki/Palindromic_number

"""

def solution(n: int = 998001) -> int:

"""

Returns the largest palindrome made from the product of two 3-digit

numbers which is less than n.

>>> solution(20000)

19591

>>> solution(30000)

29992

>>> solution(40000)

39893

>>> solution(10000)

Traceback (most recent call last):

...

ValueError: That number is larger than our acceptable range.

"""

# fetches the next number

for number in range(n - 1, 9999, -1):

str_number = str(number)

# checks whether 'str_number' is a palindrome.

if str_number == str_number[::-1]:

divisor = 999

# if 'number' is a product of two 3-digit numbers

# then number is the answer otherwise fetch next number.

while divisor != 99:

if (number % divisor == 0) and (len(str(number // divisor)) == 3.0):

return number

divisor -= 1

raise ValueError("That number is larger than our acceptable range.")

if __name__ == "__main__":

print(f"{solution() = }")

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