From 3c3d25ac7b34f5c81b3e5a599fed3e2bf2b48242 Mon Sep 17 00:00:00 2001
From: Bhumit267 <bhumitprs15101975@gmail.com>
Date: Thu, 5 Nov 2026 22:56:50 +0530
Subject: [PATCH] fix(dynamicprogramming): handle n=0 and negative inputs
 safely in CatalanNumber

---
 .../thealgorithms/dynamicprogramming/CatalanNumber.java   | 8 ++++++++
 .../dynamicprogramming/CatalanNumberTest.java             | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/src/main/java/com/thealgorithms/dynamicprogramming/CatalanNumber.java b/src/main/java/com/thealgorithms/dynamicprogramming/CatalanNumber.java
index d01066f611bd..b21beafba746 100644
--- a/src/main/java/com/thealgorithms/dynamicprogramming/CatalanNumber.java
+++ b/src/main/java/com/thealgorithms/dynamicprogramming/CatalanNumber.java
@@ -21,8 +21,16 @@ private CatalanNumber() {
      * n > 50, BigInteger class should be used instead long
      *
      * @return catalanArray[n] the nth Catalan number
+     * @throws IllegalArgumentException if n is negative
      */
     static long findNthCatalan(int n) {
+        if (n < 0) {
+            throw new IllegalArgumentException("n must be non-negative");
+        }
+        if (n <= 1) {
+            return 1;
+        }
+
         // Array to store the results of subproblems i.e Catalan numbers from [1...n-1]
         long[] catalanArray = new long[n + 1];
 
diff --git a/src/test/java/com/thealgorithms/dynamicprogramming/CatalanNumberTest.java b/src/test/java/com/thealgorithms/dynamicprogramming/CatalanNumberTest.java
index a065bb8c2a10..08dcde5decb6 100644
--- a/src/test/java/com/thealgorithms/dynamicprogramming/CatalanNumberTest.java
+++ b/src/test/java/com/thealgorithms/dynamicprogramming/CatalanNumberTest.java
@@ -1,6 +1,7 @@
 package com.thealgorithms.dynamicprogramming;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import org.junit.jupiter.api.Test;
 
@@ -8,7 +9,14 @@ public class CatalanNumberTest {
 
     @Test
     public void testCatalanNumber() {
+        assertEquals(1, CatalanNumber.findNthCatalan(0));
+        assertEquals(1, CatalanNumber.findNthCatalan(1));
         assertEquals(42, CatalanNumber.findNthCatalan(5));
         assertEquals(16796, CatalanNumber.findNthCatalan(10));
     }
+
+    @Test
+    public void testNegativeInput() {
+        assertThrows(IllegalArgumentException.class, () -> CatalanNumber.findNthCatalan(-1));
+    }
 }