Merge pull request #42 from MIT-Emerging-Talent/factorial

factorial function

solutions/factorial.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+A module for Computing the factorial of a non-negative integer n.
+
+Module contents:
+    - factorial: is the product of all positive integers less than or equal to n.
+
+Created on XX XX XX
+@author: Saad M. Ashour
+"""
+
+
+def factorial(n: int) -> int:
+    """
+    Computes the factorial of a non-negative integer n.
+
+    The factorial of a non-negative integer n
+    is the product of all positive integers less than or equal to n.
+
+    Parameters:
+        n (int): A non-negative integer.
+
+    Returns:
+        int: The factorial of the input integer n.
+
+    Raises:
+        ValueError: If n is negative, as factorial is not defined for negative numbers.
+        TypeError: If n is not an integer, as factorials are only defined for integers.
+
+    Examples:
+    >>> factorial(0)
+    1
+
+    >>> factorial(1)
+    1
+
+    >>> factorial(5)
+    120
+
+    >>> factorial(3)
+    6
+    """
+    # Validate input type and value
+    if not isinstance(n, int):
+        raise TypeError("Input must be an integer.")
+
+    if n < 0:
+        raise ValueError("Factorial is not defined for negative numbers.")
+
+    # Base case for recursion: 0! = 1
+    if n == 0 or n == 1:
+        return 1
+
+    # Recursive case: n! = n * (n-1)!
+    return n * factorial(n - 1)

solutions/tests/test_factorial.py

@@ -0,0 +1,59 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+Unit tests for factorial function.
+
+@author: Saad M. Ashour
+"""
+
+import unittest
+from solutions.factorial import factorial
+
+
+class TestFactorial(unittest.TestCase):
+    """
+    Unit tests for the factorial function.
+
+    The factorial function computes the factorial of a non-negative integer using recursion.
+    These tests verify its correctness for various inputs,
+    including edge cases, valid cases, and invalid cases.
+    """
+
+
+def test_factorial_zero(self):
+    """It should evaluate 0 to 1"""
+    actual = factorial(0)
+    expected = 1
+    self.assertEqual(actual, expected)
+
+
+def test_factorial_one(self):
+    """It should evaluate 1 to 1"""
+    actual = factorial(1)
+    expected = 1
+    self.assertEqual(actual, expected)
+
+
+def test_factorial_positive(self):
+    """It should evaluate 5 to 120"""
+    actual = factorial(5)
+    expected = 120
+    self.assertEqual(actual, expected)
+
+
+def test_factorial_negative(self):
+    """factorial of negative integer will raise Error"""
+    with self.assertRaises(ValueError):
+        factorial(-1)
+
+
+def test_factorial_non_integer(self):
+    """factorial of non integer will raise Error"""
+    with self.assertRaises(TypeError):
+        factorial(3.5)
+    with self.assertRaises(TypeError):
+        factorial("string")
+
+
+if __name__ == "__main__":
+    unittest.main()