From 90b56bc3d36a05b67cf10d0ddd237fe03e679a15 Mon Sep 17 00:00:00 2001
From: Oleksii Trekhleb <trehleb@gmail.com>
Date: Sat, 2 Jun 2018 22:11:01 +0300
Subject: [PATCH] Fix issue #37 with AVL tree.

---
 src/data-structures/tree/avl-tree/AvlTree.js  | 11 +++++
 src/data-structures/tree/avl-tree/README.md   |  1 +
 .../tree/avl-tree/__test__/AvlTRee.test.js    | 44 +++++++++++++++++++
 3 files changed, 56 insertions(+)

diff --git a/src/data-structures/tree/avl-tree/AvlTree.js b/src/data-structures/tree/avl-tree/AvlTree.js
index 204bc83b..b4b86ea4 100644
--- a/src/data-structures/tree/avl-tree/AvlTree.js
+++ b/src/data-structures/tree/avl-tree/AvlTree.js
@@ -80,6 +80,12 @@ export default class AvlTree extends BinarySearchTree {
     const leftRightNode = leftNode.right;
     leftNode.setRight(null);
 
+    // Preserve leftRightNode's left subtree.
+    if (leftRightNode.left) {
+      leftNode.setRight(leftRightNode.left);
+      leftRightNode.setLeft(null);
+    }
+
     // Attach leftRightNode to the rootNode.
     rootNode.setLeft(leftRightNode);
 
@@ -102,6 +108,11 @@ export default class AvlTree extends BinarySearchTree {
     const rightLeftNode = rightNode.left;
     rightNode.setLeft(null);
 
+    if (rightLeftNode.right) {
+      rightNode.setLeft(rightLeftNode.right);
+      rightLeftNode.setRight(null);
+    }
+
     // Attach rightLeftNode to the rootNode.
     rootNode.setRight(rightLeftNode);
 
diff --git a/src/data-structures/tree/avl-tree/README.md b/src/data-structures/tree/avl-tree/README.md
index 903da100..452a9eb4 100644
--- a/src/data-structures/tree/avl-tree/README.md
+++ b/src/data-structures/tree/avl-tree/README.md
@@ -45,3 +45,4 @@ AVL tree with balance factors (green)
 * [Tutorials Point](https://www.tutorialspoint.com/data_structures_algorithms/avl_tree_algorithm.htm)
 * [BTech](http://btechsmartclass.com/DS/U5_T2.html)
 * [AVL Tree Insertion on YouTube](https://www.youtube.com/watch?v=rbg7Qf8GkQ4&list=PLLXdhg_r2hKA7DPDsunoDZ-Z769jWn4R8&index=12&)
+* [AVL Tree Operations Visualisations](https://www.cs.usfca.edu/~galles/visualization/AVLtree.html)
diff --git a/src/data-structures/tree/avl-tree/__test__/AvlTRee.test.js b/src/data-structures/tree/avl-tree/__test__/AvlTRee.test.js
index f41c1831..5be7d119 100644
--- a/src/data-structures/tree/avl-tree/__test__/AvlTRee.test.js
+++ b/src/data-structures/tree/avl-tree/__test__/AvlTRee.test.js
@@ -185,4 +185,48 @@ describe('AvlTree', () => {
     expect(tree.root.height).toBe(2);
     expect(tree.toString()).toBe('6,8,9,18,21,22,43');
   });
+
+  it('should do left right rotation and keeping left right node safe', () => {
+    const tree = new AvlTree();
+
+    tree.insert(30);
+    tree.insert(15);
+    tree.insert(40);
+    tree.insert(10);
+    tree.insert(18);
+    tree.insert(35);
+    tree.insert(45);
+    tree.insert(5);
+    tree.insert(12);
+
+    expect(tree.toString()).toBe('5,10,12,15,18,30,35,40,45');
+    expect(tree.root.height).toBe(3);
+
+    tree.insert(11);
+
+    expect(tree.toString()).toBe('5,10,11,12,15,18,30,35,40,45');
+    expect(tree.root.height).toBe(3);
+  });
+
+  it('should do left right rotation and keeping left right node safe', () => {
+    const tree = new AvlTree();
+
+    tree.insert(30);
+    tree.insert(15);
+    tree.insert(40);
+    tree.insert(10);
+    tree.insert(18);
+    tree.insert(35);
+    tree.insert(45);
+    tree.insert(42);
+    tree.insert(47);
+
+    expect(tree.toString()).toBe('10,15,18,30,35,40,42,45,47');
+    expect(tree.root.height).toBe(3);
+
+    tree.insert(43);
+
+    expect(tree.toString()).toBe('10,15,18,30,35,40,42,43,45,47');
+    expect(tree.root.height).toBe(3);
+  });
 });