refactor: Enhance docs, add tests in AVLSimple

Author: Hardvan

src/main/java/com/thealgorithms/datastructures/trees/AVLSimple.java

@@ -1,35 +1,38 @@
 package com.thealgorithms.datastructures.trees;
 
-/*
-* Avl is algo that balance itself while adding new alues to tree
-* by rotating branches of binary tree and make itself Binary seaarch tree
-* there are four cases which has to tackle
-* rotating - left right ,left left,right right,right left
-
-Test Case:
-
-AVLTree tree=new AVLTree();
-                tree.insert(20);
-                tree.insert(25);
-                tree.insert(30);
-                tree.insert(10);
-                tree.insert(5);
-                tree.insert(15);
-                tree.insert(27);
-                tree.insert(19);
-                tree.insert(16);
-
-                tree.display();
-
-
-
-
-*/
-
+/**
+ * The AVLSimple class implements an AVL Tree, a self-balancing binary search tree.
+ * It maintains the balance of the tree using rotations during insertion to ensure that
+ * the heights of the two child subtrees of any node differ by at most one.
+ *
+ * An AVL Tree performs the following operations:
+ * - Insertion: Adds a new node while maintaining the AVL property.
+ * - Display: Outputs the structure of the tree.
+ *
+ * The AVL tree balances itself in four main cases during insertion:
+ * 1. Left-Left (LL) Case: Right rotation is performed.
+ * 2. Right-Right (RR) Case: Left rotation is performed.
+ * 3. Right-Left (RL) Case: Right rotation followed by left rotation.
+ * 4. Left-Right (LR) Case: Left rotation followed by right rotation.
+ *
+ * Example usage:
+ * <pre>
+ *     AVLSimple tree = new AVLSimple();
+ *     tree.insert(20);
+ *     tree.insert(25);
+ *     tree.insert(30);
+ *     tree.insert(10);
+ *     tree.insert(5);
+ *     tree.insert(15);
+ *     tree.insert(27);
+ *     tree.insert(19);
+ *     tree.insert(16);
+ *     tree.display();
+ * </pre>
+ */
 public class AVLSimple {
 
-    private class Node {
-
+    static class Node {
         int data;
         int height;
         Node left;
@@ -43,6 +46,11 @@ private class Node {
 
     private Node root;
 
+    /**
+     * Inserts a new value into the AVL Tree.
+     *
+     * @param data the value to be inserted
+     */
     public void insert(int data) {
         this.root = insert(this.root, data);
     }
@@ -53,12 +61,14 @@ private Node insert(Node node, int item) {
         }
         if (node.data > item) {
             node.left = insert(node.left, item);
-        }
-        if (node.data < item) {
+        } else if (node.data < item) {
             node.right = insert(node.right, item);
+        } else {
+            return node;
         }
         node.height = Math.max(height(node.left), height(node.right)) + 1;
         int bf = bf(node);
+
         // LL case
         if (bf > 1 && item < node.left.data) {
             return rightRotate(node);
@@ -81,9 +91,12 @@ private Node insert(Node node, int item) {
         return node;
     }
 
+    /**
+     * Displays the structure of the AVL Tree in a readable format.
+     */
     public void display() {
         this.display(this.root);
-        System.out.println(this.root.height);
+        System.out.println("Tree Height: " + this.root.height);
     }
 
     private void display(Node node) {
@@ -108,20 +121,38 @@ private void display(Node node) {
         }
     }
 
+    /**
+     * Returns the height of the AVL Tree.
+     *
+     * @param node the root node of the AVL Tree
+     * @return the height of the AVL Tree
+     */
     private int height(Node node) {
         if (node == null) {
             return 0;
         }
         return node.height;
     }
 
+    /**
+     * Returns the balance factor of the AVL Tree.
+     *
+     * @param node the root node of the AVL Tree
+     * @return the balance factor of the AVL Tree
+     */
     private int bf(Node node) {
         if (node == null) {
             return 0;
         }
         return height(node.left) - height(node.right);
     }
 
+    /**
+     * Performs a right rotation on the AVL Tree.
+     *
+     * @param c the root node of the AVL Tree
+     * @return the new root node of the AVL Tree
+     */
     private Node rightRotate(Node c) {
         Node b = c.left;
         Node t3 = b.right;
@@ -133,6 +164,12 @@ private Node rightRotate(Node c) {
         return b;
     }
 
+    /**
+     * Performs a left rotation on the AVL Tree.
+     *
+     * @param c the root node of the AVL Tree
+     * @return the new root node of the AVL Tree
+     */
     private Node leftRotate(Node c) {
         Node b = c.right;
         Node t3 = b.left;
@@ -143,4 +180,12 @@ private Node leftRotate(Node c) {
         b.height = Math.max(height(b.left), height(b.right)) + 1;
         return b;
     }
+
+    public int getHeight() {
+        return this.root.height;
+    }
+
+    public Node getRoot() {
+        return this.root;
+    }
 }

src/test/java/com/thealgorithms/datastructures/trees/AVLSimpleTest.java

@@ -0,0 +1,66 @@
+package com.thealgorithms.datastructures.trees;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class AVLSimpleTest {
+
+    private AVLSimple tree;
+
+    @BeforeEach
+    public void setup() {
+        tree = new AVLSimple();
+    }
+
+    @Test
+    public void testInsertAndDisplay() {
+        tree.insert(20);
+        tree.insert(30);
+        tree.insert(10);
+        tree.insert(5);
+        tree.insert(15);
+
+        // The output is not directly testable since display prints to console,
+        // so we'll check the height of the tree to verify that balancing occurred
+        assertEquals(3, tree.getHeight());
+    }
+
+    @Test
+    public void testInsertAndBalance() {
+        tree.insert(10);
+        tree.insert(20);
+        tree.insert(30); // This will cause a left rotation
+        assertEquals(20, tree.getRoot().data);
+        assertEquals(10, tree.getRoot().left.data);
+        assertEquals(30, tree.getRoot().right.data);
+    }
+
+    @Test
+    public void testInsertMultipleValues() {
+        int[] values = {30, 20, 40, 10, 25, 35, 50};
+        for (int value : values) {
+            tree.insert(value);
+        }
+        assertEquals(30, tree.getRoot().data);
+        assertEquals(20, tree.getRoot().left.data);
+        assertEquals(40, tree.getRoot().right.data);
+        assertEquals(10, tree.getRoot().left.left.data);
+        assertEquals(25, tree.getRoot().left.right.data);
+        assertEquals(35, tree.getRoot().right.left.data);
+        assertEquals(50, tree.getRoot().right.right.data);
+    }
+
+    @Test
+    public void testHeightAfterInsertions() {
+        tree.insert(50);
+        tree.insert(30);
+        tree.insert(20);
+        tree.insert(40);
+        tree.insert(70);
+        tree.insert(60);
+        tree.insert(80);
+        assertEquals(3, tree.getHeight());
+    }
+}