From eb7cc477ff5bb65ae1915f6e4e6ac852b86b0859 Mon Sep 17 00:00:00 2001
From: Koushik Sai <nyamathabadkoushik@gmail.com>
Date: Fri, 19 Dec 2025 11:40:25 +0530
Subject: [PATCH 1/2] Add recursive factorial implementation with tests

---
 .../recursion/FactorialRecursion.java         | 37 +++++++++++++++++++
 .../recursion/FactorialRecursionTest.java     | 34 +++++++++++++++++
 2 files changed, 71 insertions(+)
 create mode 100644 src/main/java/com/thealgorithms/recursion/FactorialRecursion.java
 create mode 100644 src/test/java/com/thealgorithms/recursion/FactorialRecursionTest.java

diff --git a/src/main/java/com/thealgorithms/recursion/FactorialRecursion.java b/src/main/java/com/thealgorithms/recursion/FactorialRecursion.java
new file mode 100644
index 000000000000..ac7306da40a1
--- /dev/null
+++ b/src/main/java/com/thealgorithms/recursion/FactorialRecursion.java
@@ -0,0 +1,37 @@
+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.
+     *
+     * @param n the number whose factorial is to be computed
+     * @return factorial of n
+     * @throws IllegalArgumentException if n is negative
+     */
+    public static long factorial(int n) {
+        if (n < 0) {
+            throw new IllegalArgumentException("Factorial is not defined for negative numbers");
+        }
+        if (n <= 1) {
+            return 1;
+        }
+        return n * factorial(n - 1);
+    }
+}
diff --git a/src/test/java/com/thealgorithms/recursion/FactorialRecursionTest.java b/src/test/java/com/thealgorithms/recursion/FactorialRecursionTest.java
new file mode 100644
index 000000000000..6c6f75683d33
--- /dev/null
+++ b/src/test/java/com/thealgorithms/recursion/FactorialRecursionTest.java
@@ -0,0 +1,34 @@
+package com.thealgorithms.recursion;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import org.junit.jupiter.api.Test;
+
+class FactorialRecursionTest {
+
+    @Test
+    void testFactorialOfZero() {
+        assertEquals(1, FactorialRecursion.factorial(0));
+    }
+
+    @Test
+    void testFactorialOfOne() {
+        assertEquals(1, FactorialRecursion.factorial(1));
+    }
+
+    @Test
+    void testFactorialOfPositiveNumber() {
+        assertEquals(120, FactorialRecursion.factorial(5));
+    }
+
+    @Test
+    void testFactorialOfLargerNumber() {
+        assertEquals(3628800, FactorialRecursion.factorial(10));
+    }
+
+    @Test
+    void testFactorialOfNegativeNumber() {
+        assertThrows(IllegalArgumentException.class,
+                () -> FactorialRecursion.factorial(-1));
+    }
+}

From 6bbabd827b0ec2bd485c0bddb1bc00c179c57704 Mon Sep 17 00:00:00 2001
From: Koushik Sai <nyamathabadkoushik@gmail.com>
Date: Fri, 19 Dec 2025 12:05:46 +0530
Subject: [PATCH 2/2] [STYLE] Apply clang-format

---
 .../com/thealgorithms/recursion/FactorialRecursionTest.java   | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/test/java/com/thealgorithms/recursion/FactorialRecursionTest.java b/src/test/java/com/thealgorithms/recursion/FactorialRecursionTest.java
index 6c6f75683d33..2342a5c565a4 100644
--- a/src/test/java/com/thealgorithms/recursion/FactorialRecursionTest.java
+++ b/src/test/java/com/thealgorithms/recursion/FactorialRecursionTest.java
@@ -2,6 +2,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+
 import org.junit.jupiter.api.Test;
 
 class FactorialRecursionTest {
@@ -28,7 +29,6 @@ void testFactorialOfLargerNumber() {
 
     @Test
     void testFactorialOfNegativeNumber() {
-        assertThrows(IllegalArgumentException.class,
-                () -> FactorialRecursion.factorial(-1));
+        assertThrows(IllegalArgumentException.class, () -> FactorialRecursion.factorial(-1));
     }
 }