Challenge 165 - Double Factorial

challenge_165.md

Challenge 165 - Double Factorial

Create a function that takes a number num and returns its double factorial. Mathematically, the formulas for double factorial are as follows.

num !! = num ( num - 2)( num - 4)( num - 6) ... (4)(2)

If num == 0 or num == -1, then num !! == 1 by convention.

Examples

double_factorial(0) ➞ 1

double_factorial(2) ➞ 2

double_factorial(9) ➞ 945

double_factorial(14) ➞ 645120

Notes

• Assume all input values are greater than or equal to -1.
• Double factorial is not the same as factorial * 2.

challenge_tests.py

import unittest


def double_factorial(num: int) -> int:
    return 0  # Put your code here!!!


class Test(unittest.TestCase):
    def test_1(self):
        self.assertEqual(double_factorial(-1), 1)

    def test_2(self):
        self.assertEqual(double_factorial(0), 1)

    def test_3(self):
        self.assertEqual(double_factorial(1), 1)

    def test_4(self):
        self.assertEqual(double_factorial(2), 2)

    def test_5(self):
        self.assertEqual(double_factorial(7), 105)

    def test_6(self):
        self.assertEqual(double_factorial(9), 945)

    def test_7(self):
        self.assertEqual(double_factorial(14), 645120)

    def test_8(self):
        self.assertEqual(double_factorial(22), 81749606400)

    def test_9(self):
        self.assertEqual(double_factorial(25), 7905853580625)

    def test_10(self):
        self.assertEqual(double_factorial(27), 213458046676875)


if __name__ == "__main__":
    unittest.main()

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