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Few ways to calculate factorial of the number.
"""
Few ways to calculate factorial of the number.
For my article: http://pavdmyt.com/digging-around-factorial-function/
"""
import math as m
def fact(x):
"""
Weird factorial function implementation
by hypothetical mathematician.
"""
return m.exp(sum([m.log(k) for k in range(1, x+1)]))
def iterative_fact(x):
"""
Common iterative factorial function.
"""
res = 1
for i in range(2, x + 1):
res *= i
return res
def fast_fact(x):
"""
Calculates factorial of the number faster.
"""
if x % 2:
res = x
x -= 1
else:
res = 1
i = 0
nums = range(x, 0, -2)
for num in nums:
i += num
res *= i
return res
if __name__ == '__main__':
# Tests.
import unittest
class Test(unittest.TestCase):
def test_iterative_fact(self):
for num in range(30):
self.assertEqual(iterative_fact(num), m.factorial(num))
def test_fast_fact(self):
for num in range(30):
self.assertEqual(fast_fact(num), m.factorial(num))
unittest.main()
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