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# Factorial of a number using memoization

from functools import lru_cache

@lru_cache

def factorial(num: int) -> int:

"""

>>> factorial(7)

5040

>>> factorial(-1)

Traceback (most recent call last):

...

ValueError: Number should not be negative.

>>> [factorial(i) for i in range(10)]

[1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880]

"""

if num < 0:

raise ValueError("Number should not be negative.")

return 1 if num in (0, 1) else num * factorial(num - 1)

if __name__ == "__main__":

import doctest

doctest.testmod()

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