Add tests, add IllegalArgumentException in RodCutting

DIRECTORY.md

@@ -824,6 +824,7 @@
             * [PalindromicPartitioningTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/PalindromicPartitioningTest.java)
             * [PartitionProblemTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/PartitionProblemTest.java)
             * [RegexMatchingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/RegexMatchingTest.java)
+            * [RodCuttingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/RodCuttingTest.java)
             * [ShortestCommonSupersequenceLengthTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/ShortestCommonSupersequenceLengthTest.java)
             * [SubsetCountTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/SubsetCountTest.java)
             * [SubsetSumTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/SubsetSumTest.java)

src/main/java/com/thealgorithms/dynamicprogramming/RodCutting.java

@@ -15,9 +15,13 @@ private RodCutting() {
      * @param price An array representing the prices of different pieces, where price[i-1]
      *              represents the price of a piece of length i.
      * @param n     The length of the rod to be cut.
+     * @throws IllegalArgumentException if the price array is null or empty, or if n is less than 0.
      * @return The maximum obtainable value.
      */
     public static int cutRod(int[] price, int n) {
+        if (price == null || price.length == 0) {
+            throw new IllegalArgumentException("Price array cannot be null or empty.");
+        }
         // Create an array to store the maximum obtainable values for each rod length.
         int[] val = new int[n + 1];
         val[0] = 0;

src/test/java/com/thealgorithms/dynamicprogramming/RodCuttingTest.java

@@ -0,0 +1,96 @@
+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;
+
+/**
+ * Unit tests for the RodCutting class.
+ * This test class verifies the correctness of the cutRod method for various input cases.
+ */
+class RodCuttingTest {
+
+    /**
+     * Test case for cutting a rod of length 1.
+     * The expected maximum obtainable value is the price of the piece of length 1.
+     */
+    @Test
+    void testCutRodLength1() {
+        int[] prices = {1}; // Price for piece of length 1
+        int length = 1;
+        int expectedValue = 1;
+        assertEquals(expectedValue, RodCutting.cutRod(prices, length), "The maximum obtainable value for a rod of length 1 should be 1.");
+    }
+
+    /**
+     * Test case for cutting a rod of length 2.
+     * The expected maximum obtainable value is the best price combination for length 2.
+     */
+    @Test
+    void testCutRodLength2() {
+        int[] prices = {1, 5}; // Prices for lengths 1 and 2
+        int length = 2;
+        int expectedValue = 5; // Best value is to cut it into a single piece of length 2
+        assertEquals(expectedValue, RodCutting.cutRod(prices, length), "The maximum obtainable value for a rod of length 2 should be 5.");
+    }
+
+    /**
+     * Test case for cutting a rod of length 3.
+     * The expected maximum obtainable value is the best price combination for length 3.
+     */
+    @Test
+    void testCutRodLength3() {
+        int[] prices = {1, 5, 8}; // Prices for lengths 1, 2, and 3
+        int length = 3;
+        int expectedValue = 8; // Best value is to cut it into a single piece of length 3
+        assertEquals(expectedValue, RodCutting.cutRod(prices, length), "The maximum obtainable value for a rod of length 3 should be 8.");
+    }
+
+    /**
+     * Test case for cutting a rod of length 4.
+     * The expected maximum obtainable value is the best price combination for length 4.
+     */
+    @Test
+    void testCutRodLength4() {
+        int[] prices = {1, 5, 8, 9}; // Prices for lengths 1, 2, 3, and 4
+        int length = 4;
+        int expectedValue = 10; // Best value is to cut it into two pieces of length 2
+        assertEquals(expectedValue, RodCutting.cutRod(prices, length), "The maximum obtainable value for a rod of length 4 should be 10.");
+    }
+
+    /**
+     * Test case for cutting a rod of length 5.
+     * The expected maximum obtainable value is the best price combination for length 5.
+     */
+    @Test
+    void testCutRodLength5() {
+        int[] prices = {1, 5, 8, 9, 10}; // Prices for lengths 1, 2, 3, 4, and 5
+        int length = 5;
+        int expectedValue = 13; // Best value is to cut it into pieces of lengths 2 and 3
+        assertEquals(expectedValue, RodCutting.cutRod(prices, length), "The maximum obtainable value for a rod of length 5 should be 13.");
+    }
+
+    /**
+     * Test case for cutting a rod of length 0.
+     * The expected maximum obtainable value should be 0 since the rod has no length.
+     */
+    @Test
+    void testCutRodLength0() {
+        int[] prices = {1, 5, 8, 9, 10}; // Prices are irrelevant for length 0
+        int length = 0;
+        int expectedValue = 0; // No value obtainable from a rod of length 0
+        assertEquals(expectedValue, RodCutting.cutRod(prices, length), "The maximum obtainable value for a rod of length 0 should be 0.");
+    }
+
+    /**
+     * Test case for an empty prices array.
+     * The expected maximum obtainable value should still be 0 for any length.
+     */
+    @Test
+    void testCutRodEmptyPrices() {
+        int[] prices = {};
+        int length = 5;
+        assertThrows(IllegalArgumentException.class, () -> RodCutting.cutRod(prices, length), "An empty prices array should throw an IllegalArgumentException.");
+    }
+}