mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-11-24 05:21:09 +00:00
4761fef1a5
* Adding the double factorial algorithm * Adding the double factorial algorithm Co-authored-by: Jonathan Ocles <jocles@chiang.ec>
34 lines
974 B
Python
34 lines
974 B
Python
def double_factorial(num: int) -> int:
|
|
"""
|
|
Compute double factorial using iterative method.
|
|
|
|
To learn about the theory behind this algorithm:
|
|
https://en.wikipedia.org/wiki/Double_factorial
|
|
|
|
>>> import math
|
|
>>> all(double_factorial(i) == math.prod(range(i, 0, -2)) for i in range(20))
|
|
True
|
|
>>> double_factorial(0.1)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: double_factorial() only accepts integral values
|
|
>>> double_factorial(-1)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: double_factorial() not defined for negative values
|
|
"""
|
|
if not isinstance(num, int):
|
|
raise ValueError("double_factorial() only accepts integral values")
|
|
if num < 0:
|
|
raise ValueError("double_factorial() not defined for negative values")
|
|
value = 1
|
|
for i in range(num, 0, -2):
|
|
value *= i
|
|
return value
|
|
|
|
|
|
if __name__ == "__main__":
|
|
import doctest
|
|
|
|
doctest.testmod()
|