Avl tree node insertion in kotlin

Kotlin program for Avl tree node insertion. Here problem description and other solutions.

// Kotlin program
// AVL Tree insertion

// Avl Tree Node
class TreeNode
{
	var data: Int;
	var height: Int;
	var left: TreeNode ? ;
	var right: TreeNode ? ;
	constructor(data: Int)
	{
		// Set node value of avl tree
		this.data = data;
		this.height = 1;
		this.left = null;
		this.right = null;
	}
}
class AvlTree
{
	// Tree root node
	var root: TreeNode ? ;
	constructor()
	{
		this.root = null;
	}
	// Get the height of given node
	fun getHeight(node: TreeNode ? ): Int
	{
		if (node == null)
		{
			return 0;
		}
		return node.height;
	}
	// Get the max value of given two numbers
	fun maxHeight(a: Int, b: Int): Int
	{
		if (a > b)
		{
			return a;
		}
		else
		{
			return b;
		}
	}
	// Perform the Right rotate operation
	fun rightRotate(node: TreeNode ? ): TreeNode ?
	{
		// Get left child node
		val leftNode: TreeNode? = node?.left;
		// Get left node right subtree
		val rightSubtree: TreeNode? = leftNode?.right;
		// Update the left and right subtree
		leftNode?.right = node;
		node?.left = rightSubtree;
		// Change the height of modified node
		node!!.height = this.maxHeight(
      this.getHeight(node.left), this.getHeight(node.right)) + 1;
		leftNode!!.height = this.maxHeight(
          this.getHeight(leftNode.left), 
          this.getHeight(leftNode.right)) + 1;
		return leftNode;
	}
	// Perform the Left Rotate operation
	fun leftRotate(node: TreeNode ? ): TreeNode ?
	{
		// Get right child node
		val rightNode: TreeNode? = node?.right;
		// Get right node left subtree
		val leftSubtree: TreeNode? = rightNode?.left;
		// Update the left and right subtree
		rightNode?.left = node;
		node?.right = leftSubtree;
		// Change the height of modified node
		node!!.height = this.maxHeight(
      this.getHeight(node.left), 
        this.getHeight(node.right)) + 1;
		rightNode!!.height = this.maxHeight(
          this.getHeight(rightNode.left), 
          this.getHeight(rightNode.right)) + 1;
		return rightNode;
	}
	// Get the balance factor
	fun getBalanceFactor(node: TreeNode ? ): Int
	{
		if (node == null)
		{
			return 0;
		}
		return this.getHeight(node.left) - 
          this.getHeight(node.right);
	}
	// Recursively, add a node in AVL tree
	// Duplicate keys (data) are not allowed
	fun addNode(node: TreeNode ? , data : Int): TreeNode ?
	{
		if (node == null)
		{
			// Return a new node
			return TreeNode(data);
		}
		if (data < node.data)
		{
			node.left = this.addNode(node.left, data);
		}
		else if (data > node.data)
		{
			node.right = this.addNode(node.right, data);
		}
		else
		{
			// When given key data already exists
			return node;
		}
		// Change the height of current node
		node.height = 1 + this.maxHeight(
          this.getHeight(node.left), this.getHeight(node.right));
		// Get balance factor of a node
		val factor: Int = this.getBalanceFactor(node);
		// LL Case
		if (factor > 1 && data < node.left!!.data)
		{
			return this.rightRotate(node);
		}
		// RR Case
		if (factor < -1 && data > node.right!!.data)
		{
			return this.leftRotate(node);
		}
		// LL Case
		if (factor > 1 && data > node.left!!.data)
		{
			node.left = this.leftRotate(node.left);
			return this.rightRotate(node);
		}
		// RR Case
		if (factor < -1 && data < node.right!!.data)
		{
			node.right = this.rightRotate(node.right);
			return this.leftRotate(node);
		}
		return node;
	}
	// Print the tree in preorder form
	fun preorder(node: TreeNode ? ): Unit
	{
		if (node != null)
		{
			print("  " + node.data);
			this.preorder(node.left);
			this.preorder(node.right);
		}
	}
	// Print the tree in inorder form
	fun inorder(node: TreeNode ? ): Unit
	{
		if (node != null)
		{
			this.inorder(node.left);
			print("  " + node.data);
			this.inorder(node.right);
		}
	}
	// Print the tree in postorder form
	fun postorder(node: TreeNode ? ): Unit
	{
		if (node != null)
		{
			this.postorder(node.left);
			this.postorder(node.right);
			print("  " + node.data);
		}
	}
}
fun main(args: Array < String > ): Unit
{
	val tree: AvlTree = AvlTree();
	// Add tree node
	tree.root = tree.addNode(tree.root, 4);
	tree.root = tree.addNode(tree.root, 7);
	tree.root = tree.addNode(tree.root, 5);
	tree.root = tree.addNode(tree.root, 19);
	tree.root = tree.addNode(tree.root, 17);
	tree.root = tree.addNode(tree.root, 13);
	tree.root = tree.addNode(tree.root, 11);
	tree.root = tree.addNode(tree.root, 3);
	tree.root = tree.addNode(tree.root, 2);
	tree.root = tree.addNode(tree.root, -3);
	/*
	  Resultant  AVL Tree
	  -----------------
	         7
	        /  \ 
	       /    \
	      4      17
	     / \     / \
	    2   5  13  19
	   / \     /
	 -3   3   11
	*/
	print("Resultant AVL Tree");
	print("\nPreorder  :");
	tree.preorder(tree.root);
	print("\nInorder   :");
	tree.inorder(tree.root);
	print("\nPostorder :");
	tree.postorder(tree.root);
}

Output

Resultant AVL Tree
Preorder  :  7  4  2  -3  3  5  17  13  11  19
Inorder   :  -3  2  3  4  5  7  11  13  17  19
Postorder :  -3  3  2  5  4  11  13  19  17  7


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