Move recursive factorial to recursion package and remove duplicate

Author: Koushik Sai

src/main/java/com/thealgorithms/maths/FactorialRecursion.java

@@ -1,37 +1,18 @@
 package com.thealgorithms.recursion;
 
-/*
- * Factorial of a number n is the product of all positive integers less than
- * or equal to n.
- *
- * n! = n × (n - 1) × (n - 2) × ... × 1
- *
- * Examples:
- * 0! = 1
- * 1! = 1
- * 5! = 120
- */
-
 public final class FactorialRecursion {
-
     private FactorialRecursion() {
-        throw new UnsupportedOperationException("Utility class");
     }
-
     /**
-     * Computes the factorial of a non-negative integer using recursion.
+     * Recursive FactorialRecursion Method
      *
-     * @param n the number whose factorial is to be computed
-     * @return factorial of n
-     * @throws IllegalArgumentException if n is negative
+     * @param n The number to factorial
+     * @return The factorial of the number
      */
     public static long factorial(int n) {
         if (n < 0) {
-            throw new IllegalArgumentException("Factorial is not defined for negative numbers");
-        }
-        if (n <= 1) {
-            return 1;
+            throw new IllegalArgumentException("number is negative");
         }
-        return n * factorial(n - 1);
+        return n == 0 || n == 1 ? 1 : n * factorial(n - 1);
     }
 }

src/main/java/com/thealgorithms/recursion/FactorialRecursion.java

@@ -1,34 +1,29 @@
 package com.thealgorithms.recursion;
 
+import java.util.stream.Stream;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
-
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
-class FactorialRecursionTest {
-
-    @Test
-    void testFactorialOfZero() {
-        assertEquals(1, FactorialRecursion.factorial(0));
-    }
-
-    @Test
-    void testFactorialOfOne() {
-        assertEquals(1, FactorialRecursion.factorial(1));
-    }
+import com.thealgorithms.recursion.FactorialRecursion;
 
-    @Test
-    void testFactorialOfPositiveNumber() {
-        assertEquals(120, FactorialRecursion.factorial(5));
+public class FactorialRecursionTest {
+    @ParameterizedTest
+    @MethodSource("inputStream")
+    void testFactorialRecursion(long expected, int number) {
+        assertEquals(expected, FactorialRecursion.factorial(number));
     }
 
-    @Test
-    void testFactorialOfLargerNumber() {
-        assertEquals(3628800, FactorialRecursion.factorial(10));
+    private static Stream<Arguments> inputStream() {
+        return Stream.of(Arguments.of(1, 0), Arguments.of(1, 1), Arguments.of(2, 2), Arguments.of(6, 3), Arguments.of(120, 5));
     }
 
     @Test
-    void testFactorialOfNegativeNumber() {
+    void testThrowsForNegativeInput() {
         assertThrows(IllegalArgumentException.class, () -> FactorialRecursion.factorial(-1));
     }
 }