test: LongestAlternatingSubsequenceTest (#5399)

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

@@ -1,38 +1,48 @@
 package com.thealgorithms.dynamicprogramming;
 
-/*
-
- * Problem Statement: -
- * Find Longest Alternating Subsequence
-
- * A sequence {x1, x2, .. xn} is alternating sequence if its elements satisfy one of the following
- relations :
-
-   x1 < x2 > x3 < x4 > x5 < …. xn or
-   x1 > x2 < x3 > x4 < x5 > …. xn
+/**
+ * Class for finding the length of the longest alternating subsequence in an array.
+ *
+ * <p>An alternating sequence is a sequence of numbers where the elements alternate
+ * between increasing and decreasing. Specifically, a sequence is alternating if its elements
+ * satisfy one of the following relations:
+ *
+ * <ul>
+ *   <li>{@code x1 < x2 > x3 < x4 > x5 < ... < xn}</li>
+ *   <li>{@code x1 > x2 < x3 > x4 < x5 > ... > xn}</li>
+ * </ul>
+ *
+ * <p>This class provides a method to compute the length of the longest such subsequence
+ * from a given array of integers.
  */
 public final class LongestAlternatingSubsequence {
     private LongestAlternatingSubsequence() {
     }
 
-    /* Function to return longest alternating subsequence length*/
-    static int alternatingLength(int[] arr, int n) {
-        /*
-
-                las[i][0] = Length of the longest
-                        alternating subsequence ending at
-                        index i and last element is
-                        greater than its previous element
-
-                las[i][1] = Length of the longest
-                        alternating subsequence ending at
-                        index i and last element is
-                        smaller than its previous
-                        element
-
+    /**
+     * Finds the length of the longest alternating subsequence in the given array.
+     *
+     * @param arr an array of integers where the longest alternating subsequence is to be found
+     * @param n the length of the array {@code arr}
+     * @return the length of the longest alternating subsequence
+     *
+     * <p>The method uses dynamic programming to solve the problem. It maintains a 2D array
+     * {@code las} where:
+     * <ul>
+     *   <li>{@code las[i][0]} represents the length of the longest alternating subsequence
+     *   ending at index {@code i} with the last element being greater than the previous element.</li>
+     *   <li>{@code las[i][1]} represents the length of the longest alternating subsequence
+     *   ending at index {@code i} with the last element being smaller than the previous element.</li>
+     * </ul>
+     *
+     * <p>The method iterates through the array and updates the {@code las} array based on
+     * whether the current element is greater or smaller than the previous elements.
+     * The result is the maximum value found in the {@code las} array.
      */
+    static int alternatingLength(int[] arr, int n) {
         int[][] las = new int[n][2]; // las = LongestAlternatingSubsequence
 
+        // Initialize the dp array
         for (int i = 0; i < n; i++) {
             las[i][0] = 1;
             las[i][1] = 1;
@@ -40,34 +50,24 @@ public final class LongestAlternatingSubsequence {
 
         int result = 1; // Initialize result
 
-        /* Compute values in bottom up manner */
+        // Compute values in a bottom-up manner
         for (int i = 1; i < n; i++) {
-            /* Consider all elements as previous of arr[i]*/
             for (int j = 0; j < i; j++) {
-                /* If arr[i] is greater, then check with las[j][1] */
+                // If arr[i] is greater than arr[j], update las[i][0]
                 if (arr[j] < arr[i] && las[i][0] < las[j][1] + 1) {
                     las[i][0] = las[j][1] + 1;
                 }
 
-                /* If arr[i] is smaller, then check with las[j][0]*/
+                // If arr[i] is smaller than arr[j], update las[i][1]
                 if (arr[j] > arr[i] && las[i][1] < las[j][0] + 1) {
                     las[i][1] = las[j][0] + 1;
                 }
             }
 
-            /* Pick maximum of both values at index i */
-            if (result < Math.max(las[i][0], las[i][1])) {
-                result = Math.max(las[i][0], las[i][1]);
-            }
+            // Pick the maximum of both values at index i
+            result = Math.max(result, Math.max(las[i][0], las[i][1]));
         }
 
         return result;
     }
-
-    public static void main(String[] args) {
-        int[] arr = {10, 22, 9, 33, 49, 50, 31, 60};
-        int n = arr.length;
-        System.out.println("Length of Longest "
-            + "alternating subsequence is " + alternatingLength(arr, n));
-    }
 }

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

@@ -0,0 +1,22 @@
+package com.thealgorithms.dynamicprogramming;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class LongestAlternatingSubsequenceTest {
+
+    @ParameterizedTest
+    @MethodSource("provideTestCases")
+    void testAlternatingLength(int[] arr, int expected) {
+        assertEquals(expected, LongestAlternatingSubsequence.alternatingLength(arr, arr.length));
+    }
+
+    private static Stream<Arguments> provideTestCases() {
+        return Stream.of(Arguments.of(new int[] {1}, 1), Arguments.of(new int[] {1, 2}, 2), Arguments.of(new int[] {2, 1}, 2), Arguments.of(new int[] {1, 3, 2, 4, 3, 5}, 6), Arguments.of(new int[] {1, 2, 3, 4, 5}, 2), Arguments.of(new int[] {5, 4, 3, 2, 1}, 2),
+            Arguments.of(new int[] {10, 22, 9, 33, 49, 50, 31, 60}, 6), Arguments.of(new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 2));
+    }
+}