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Enhance docs, add tests in AVLTree (TheAlgorithms#6058)
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‎DIRECTORY.md

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@@ -912,6 +912,7 @@
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* [StackArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayTest.java)
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* [StackOfLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackOfLinkedListTest.java)
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* trees
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* [AVLTreeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/AVLTreeTest.java)
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* [BinaryTreeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/BinaryTreeTest.java)
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* [BoundaryTraversalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/BoundaryTraversalTest.java)
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* [BSTFromSortedArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/BSTFromSortedArrayTest.java)

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

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@@ -1,11 +1,19 @@
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package com.thealgorithms.datastructures.trees;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* Represents an AVL Tree, a self-balancing binary search tree.
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* In an AVL tree, the heights of the two child subtrees of any node
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* differ by at most one. If they differ by more than one at any time,
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* rebalancing is performed to restore this property.
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*/
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public class AVLTree {
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private Node root;
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7-
private class Node {
8-
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private static class Node {
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private int key;
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private int balance;
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private int height;
@@ -17,8 +25,18 @@ private class Node {
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key = k;
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parent = p;
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}
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public Integer getBalance() {
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return balance;
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}
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}
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/**
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* Inserts a new key into the AVL tree.
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*
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* @param key the key to be inserted
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* @return {@code true} if the key was inserted, {@code false} if the key already exists
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*/
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public boolean insert(int key) {
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if (root == null) {
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root = new Node(key, null);
@@ -31,7 +49,6 @@ public boolean insert(int key) {
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}
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parent = n;
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boolean goLeft = n.key > key;
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n = goLeft ? n.left : n.right;
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@@ -49,8 +66,32 @@ public boolean insert(int key) {
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return true;
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}
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/**
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* Deletes a key from the AVL tree.
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*
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* @param delKey the key to be deleted
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*/
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public void delete(int delKey) {
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if (root == null) {
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return;
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}
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// Find the node to be deleted
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Node node = root;
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Node child = root;
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while (child != null) {
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node = child;
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child = delKey >= node.key ? node.right : node.left;
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if (delKey == node.key) {
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delete(node);
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return;
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}
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}
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}
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private void delete(Node node) {
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if (node.left == null && node.right == null) {
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// Leaf node
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if (node.parent == null) {
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root = null;
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} else {
@@ -64,6 +105,8 @@ private void delete(Node node) {
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}
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return;
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}
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// Node has one or two children
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Node child;
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if (node.left != null) {
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child = node.left;
@@ -80,26 +123,49 @@ private void delete(Node node) {
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delete(child);
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}
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83-
public void delete(int delKey) {
84-
if (root == null) {
85-
return;
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/**
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* Returns a list of balance factors for each node in the tree.
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*
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* @return a list of integers representing the balance factors of the nodes
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*/
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public List<Integer> returnBalance() {
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List<Integer> balances = new ArrayList<>();
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returnBalance(root, balances);
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return balances;
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}
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private void returnBalance(Node n, List<Integer> balances) {
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if (n != null) {
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returnBalance(n.left, balances);
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balances.add(n.getBalance());
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returnBalance(n.right, balances);
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}
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Node node = root;
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Node child = root;
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}
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90-
while (child != null) {
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node = child;
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child = delKey >= node.key ? node.right : node.left;
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if (delKey == node.key) {
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delete(node);
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return;
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}
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/**
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* Searches for a key in the AVL tree.
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*
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* @param key the key to be searched
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* @return true if the key is found, false otherwise
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*/
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public boolean search(int key) {
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Node result = searchHelper(this.root, key);
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return result != null;
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}
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private Node searchHelper(Node root, int key) {
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if (root == null || root.key == key) {
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return root;
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}
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if (root.key > key) {
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return searchHelper(root.left, key);
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}
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return searchHelper(root.right, key);
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}
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100167
private void rebalance(Node n) {
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setBalance(n);
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103169
if (n.balance == -2) {
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if (height(n.left.left) >= height(n.left.right)) {
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n = rotateRight(n);
@@ -143,7 +209,6 @@ private Node rotateLeft(Node a) {
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}
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setBalance(a, b);
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return b;
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}
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@@ -169,7 +234,6 @@ private Node rotateRight(Node a) {
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}
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setBalance(a, b);
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return b;
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}
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@@ -197,53 +261,9 @@ private void setBalance(Node... nodes) {
197261
}
198262
}
199263

200-
public void printBalance() {
201-
printBalance(root);
202-
}
203-
204-
private void printBalance(Node n) {
205-
if (n != null) {
206-
printBalance(n.left);
207-
System.out.printf("%s ", n.balance);
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printBalance(n.right);
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}
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}
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private void reheight(Node node) {
213265
if (node != null) {
214266
node.height = 1 + Math.max(height(node.left), height(node.right));
215267
}
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}
217-
218-
public boolean search(int key) {
219-
Node result = searchHelper(this.root, key);
220-
return result != null;
221-
}
222-
223-
private Node searchHelper(Node root, int key) {
224-
// root is null or key is present at root
225-
if (root == null || root.key == key) {
226-
return root;
227-
}
228-
229-
// key is greater than root's key
230-
if (root.key > key) {
231-
return searchHelper(root.left, key); // call the function on the node's left child
232-
}
233-
// key is less than root's key then
234-
// call the function on the node's right child as it is greater
235-
return searchHelper(root.right, key);
236-
}
237-
238-
public static void main(String[] args) {
239-
AVLTree tree = new AVLTree();
240-
241-
System.out.println("Inserting values 1 to 10");
242-
for (int i = 1; i < 10; i++) {
243-
tree.insert(i);
244-
}
245-
246-
System.out.print("Printing balance: ");
247-
tree.printBalance();
248-
}
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}

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

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package com.thealgorithms.datastructures.trees;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertFalse;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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7+
import java.util.List;
8+
import org.junit.jupiter.api.BeforeEach;
9+
import org.junit.jupiter.api.Test;
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11+
public class AVLTreeTest {
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private AVLTree avlTree;
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14+
@BeforeEach
15+
public void setUp() {
16+
avlTree = new AVLTree();
17+
}
18+
19+
@Test
20+
public void testInsert() {
21+
assertTrue(avlTree.insert(10));
22+
assertTrue(avlTree.insert(20));
23+
assertTrue(avlTree.insert(5));
24+
assertFalse(avlTree.insert(10)); // Duplicate
25+
}
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27+
@Test
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public void testSearch() {
29+
avlTree.insert(15);
30+
avlTree.insert(25);
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assertTrue(avlTree.search(15));
32+
assertFalse(avlTree.search(30)); // Not in the tree
33+
}
34+
35+
@Test
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public void testDeleteLeafNode() {
37+
avlTree.insert(10);
38+
avlTree.insert(20);
39+
avlTree.insert(30);
40+
avlTree.delete(30);
41+
assertFalse(avlTree.search(30));
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}
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@Test
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public void testDeleteNodeWithOneChild() {
46+
avlTree.insert(20);
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avlTree.insert(10);
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avlTree.insert(30);
49+
avlTree.delete(10);
50+
assertFalse(avlTree.search(10));
51+
}
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53+
@Test
54+
public void testDeleteNodeWithTwoChildren() {
55+
avlTree.insert(20);
56+
avlTree.insert(10);
57+
avlTree.insert(30);
58+
avlTree.insert(25);
59+
avlTree.delete(20);
60+
assertFalse(avlTree.search(20));
61+
assertTrue(avlTree.search(30));
62+
assertTrue(avlTree.search(25));
63+
}
64+
65+
@Test
66+
public void testReturnBalance() {
67+
avlTree.insert(10);
68+
avlTree.insert(20);
69+
avlTree.insert(5);
70+
List<Integer> balances = avlTree.returnBalance();
71+
assertEquals(3, balances.size()); // There should be 3 nodes
72+
assertEquals(0, balances.get(0)); // Balance for node 5
73+
assertEquals(0, balances.get(1)); // Balance for node 10
74+
assertEquals(0, balances.get(2)); // Balance for node 20
75+
}
76+
77+
@Test
78+
public void testInsertAndRebalance() {
79+
avlTree.insert(30);
80+
avlTree.insert(20);
81+
avlTree.insert(10); // This should cause a right rotation
82+
assertTrue(avlTree.search(20));
83+
assertTrue(avlTree.search(10));
84+
assertTrue(avlTree.search(30));
85+
}
86+
87+
@Test
88+
public void testComplexInsertionAndDeletion() {
89+
avlTree.insert(30);
90+
avlTree.insert(20);
91+
avlTree.insert(10);
92+
avlTree.insert(25);
93+
avlTree.insert(5);
94+
avlTree.insert(15);
95+
96+
avlTree.delete(20); // Test deletion
97+
assertFalse(avlTree.search(20));
98+
assertTrue(avlTree.search(30));
99+
assertTrue(avlTree.search(25));
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}
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}

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