mirror of
https://github.com/TheAlgorithms/Python.git
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b60a94b5b3
* merge double_factorial * fix ruff error * fix merge issues * change test case * fix import error
61 lines
2.0 KiB
Python
61 lines
2.0 KiB
Python
def double_factorial_recursive(n: int) -> int:
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"""
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Compute double factorial using recursive method.
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Recursion can be costly for large numbers.
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To learn about the theory behind this algorithm:
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https://en.wikipedia.org/wiki/Double_factorial
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>>> from math import prod
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>>> all(double_factorial_recursive(i) == prod(range(i, 0, -2)) for i in range(20))
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True
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>>> double_factorial_recursive(0.1)
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Traceback (most recent call last):
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...
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ValueError: double_factorial_recursive() only accepts integral values
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>>> double_factorial_recursive(-1)
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Traceback (most recent call last):
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...
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ValueError: double_factorial_recursive() not defined for negative values
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"""
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if not isinstance(n, int):
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raise ValueError("double_factorial_recursive() only accepts integral values")
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if n < 0:
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raise ValueError("double_factorial_recursive() not defined for negative values")
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return 1 if n <= 1 else n * double_factorial_recursive(n - 2)
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def double_factorial_iterative(num: int) -> int:
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"""
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Compute double factorial using iterative method.
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To learn about the theory behind this algorithm:
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https://en.wikipedia.org/wiki/Double_factorial
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>>> from math import prod
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>>> all(double_factorial_iterative(i) == prod(range(i, 0, -2)) for i in range(20))
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True
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>>> double_factorial_iterative(0.1)
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Traceback (most recent call last):
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...
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ValueError: double_factorial_iterative() only accepts integral values
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>>> double_factorial_iterative(-1)
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Traceback (most recent call last):
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...
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ValueError: double_factorial_iterative() not defined for negative values
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"""
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if not isinstance(num, int):
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raise ValueError("double_factorial_iterative() only accepts integral values")
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if num < 0:
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raise ValueError("double_factorial_iterative() not defined for negative values")
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value = 1
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for i in range(num, 0, -2):
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value *= i
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return value
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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