Added permutations_combinations.py

Author: VarunS2002

permutations_combinations.py

@@ -0,0 +1,38 @@
+from typing import Callable, Optional
+
+from factorial import Factorial
+
+
+class PermutationsCombinations:
+    @staticmethod
+    def npr(n: int, r: int) -> int:
+        if not isinstance(n, int) or not isinstance(r, int):
+            raise ArithmeticError("Cannot calculate nPr for non-integers.")
+        elif not n >= r >= 0:
+            raise ArithmeticError("Please enter n ≥ r ≥ 0.")
+        factorial: Callable[[int, Optional[bool]], int] = Factorial.factorial_iteration
+        return factorial(n) // factorial(n - r)
+
+    @staticmethod
+    def permutations(n: int, r: int) -> int:
+        return PermutationsCombinations.npr(n, r)
+
+    @staticmethod
+    def ncr(n: int, r: int) -> int:
+        if not isinstance(n, int) or not isinstance(r, int):
+            raise ArithmeticError("Cannot calculate nCr for non-integers.")
+        elif not n >= r >= 0:
+            raise ArithmeticError("Please enter n ≥ r ≥ 0.")
+        factorial: Callable[[int, Optional[bool]], int] = Factorial.factorial_iteration
+        return factorial(n) // (factorial(r) * factorial(n - r))
+
+    @staticmethod
+    def combinations(n: int, r: int) -> int:
+        return PermutationsCombinations.ncr(n, r)
+
+
+if __name__ == '__main__':
+    input_n = int(input("Enter n: "))
+    input_r = int(input("Enter r: "))
+    print("Permutations:", PermutationsCombinations.permutations(n=input_n, r=input_r))
+    print("Combinations:", PermutationsCombinations.combinations(n=input_n, r=input_r))