Balancing in AVL tree only in main root - avl-tree

Question

I am creating AVL binary tree in which the only problem is that the root is not changes its position or gets balance except all other child's root or leaves etc
Any help would be greatly appreciated!
Logical Layer file
public class Node
{
public int data;
public Node left, right;
public Node(int data)
{
this.data = data;
left = null;
right = null;
}
}
public class BinaryTree
{
public Node root;
public BinaryTree()
{
root = null;
}
public int height(Node temp)
{
int h = 0;
if (temp != null)
{
int l_height = height(temp.left);
int r_height = height(temp.right);
int max_height = Math.Max(l_height, r_height);
h = max_height + 1;
}
return h;
}
public int diff(Node temp)
{
int l_height = height(temp.left);
int r_height = height(temp.right);
int b_factor = l_height - r_height;
return b_factor;
}
Node rr_rotation(Node parent)
{
Node temp;
temp = parent.right;
parent.right = temp.left;
temp.left = parent;
return temp;
}
Node ll_rotation(Node parent)
{
Node temp;
temp = parent.left;
parent.left = temp.right;
temp.right = parent;
return temp;
}
Node lr_rotation(Node parent)
{
Node temp;
temp = parent.left;
parent.left = rr_rotation(temp);
return ll_rotation(parent);
}
Node rl_rotation(Node parent)
{
Node temp;
temp = parent.right;
parent.right = ll_rotation(temp);
return rr_rotation(parent);
}
Node balance(Node temp)
{
int bal_factor = diff(temp);
if (bal_factor > 1)
{
if (diff(temp.left) > 0)
temp = ll_rotation(temp);
else
temp = lr_rotation(temp);
}
else if (bal_factor < -1)
{
if (diff(temp.right) > 0)
temp = rl_rotation(temp);
else
temp = rr_rotation(temp);
}
return temp;
}
public Node addNode(int data) // It only add the Root(that is 55 in the fig)
{
Node newNode = new Node(data);
if (root == null)
{
root = newNode;
}
return root;
}
public Node insertNode(Node root, int newNode) //But I want to make this should add root node.
{
if (root == null) (I think here is some problem)
{
root = new Node(newNode);
root.data = newNode;
root.left = null;
root.right = null;
return root;
}
if (newNode < root.data)
{
root.left = insertNode(root.left, newNode);
root = balance(root);
}
else if (newNode >= root.data)
{
root.right = insertNode(root.right, newNode);
root = balance(root);
}
return root;
}
}
Presentataion layer file
public partial class PresentationLayer : Form
{
BinaryTree obj = new BinaryTree();
int a, b;
public PresentationLayer()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e) //add node button
{
int num = 0;
bool result = int.TryParse(textBox1.Text, out num);
if (result)
{
a = Int32.Parse(textBox1.Text);
obj.addNode(a); //It creates root
textBox1.Hide();
button1.Hide();
}
}
private void button2_Click_1(object sender, EventArgs e) //insert button
{
int num = 0;
bool result = int.TryParse(textBox2.Text, out num);
if (result)
{
b = Int32.Parse(textBox2.Text);
Node abc = new Node(b);
obj.insertNode(obj.root, b); //It is not creating root
textBox2.Clear();
}
}
}
}
Any help would be greatly appreciated!

Answer 1

You should add cases into the ll_rotation and rr_rotation functions to handle when the root is rotated. You should be able to check if the parameter parent is the same node as root, and if so, set root to refer to the new rotated node.
For example, per Wikipedia's example of left rotation:
P
/ \
/ \
A Q
/ \
B C
Rotates Left to become:
Q
/ \
/ \
P C
/ \
A B
If ll_rotation(P) is called where P is the same node as root, then the function should assign Q to be the new root