Self Balancing Tree

Problem Statement :

An AVL tree (Georgy Adelson-Velsky and Landis' tree, named after the inventors) is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property.

We define balance factor for each node as :

balanceFactor = height(left subtree) - height(right subtree)
The balance factor of any node of an AVL tree is in the integer range [-1,+1]. If after any modification in the tree, the balance factor becomes less than −1 or greater than +1, the subtree rooted at this node is unbalanced, and a rotation is needed.


You are given a pointer to the root of an AVL tree. You need to insert a value into this tree and perform the necessary rotations to ensure that it remains balanced.

Input Format

You are given a function,

node *insert(node * root,int new_val)

'node' is defined as :

struct node
int val;            //value
struct node* left;  //left child
struct node* right; //right child
int ht;             //height of the node
} node;
You only need to complete the function.

Note: All the values in the tree will be distinct. Height of a Null node is -1 and the height of the leaf node is 0.

Output Format

Insert the new value into the tree and return a pointer to the root of the tree. Ensure that the tree remains balanced.

Sample Input

  /  \
 2    4
The value to be inserted is 6.

Solution :

                            Solution in C :

In C++ :

/* Node is defined as :
typedef struct node
    int val;
    struct node* left;
    struct node* right;
    int ht;
} node; */

node * insert(node * T,int x)
    if (T == NULL)
        T = (node*)malloc(sizeof(node));
        T->val = x;
        T->left = NULL;
        T->right = NULL;
    else if (x > T->val)
        T->right = insert_hidden(T->right, x);
        if (BF_hidden(T) == -2)
            if (x > T->right->val)
                T = RR_hidden(T);
                T = RL_hidden(T);
    else if (x < T->val)
        T->left = insert_hidden(T->left, x);
        if (BF_hidden(T) == 2){
            if (x < T->left->val)
                T = LL_hidden(T);
                T = LR_hidden(T);
    T->ht = ht_hidden(T);

In Java :

   /* Class node is defined as :
    class Node 
       int val;   //Value
       int ht;      //Height
       Node left;   //Left child
       Node right;   //Right child


static Node insert(Node root,int val) {
    Node newNode = new Node(); 
    newNode.val = val; = 0;
    newNode.left = null;
    newNode.right = null;
    if (root==null) {
        root = newNode;
    } else {
        root=avlinsert(newNode, root);
    return root;

// return height of tree rooted at x
static public int height(Node x) {
    if (x == null) return -1;
    else return;

static public Node rotatewithleft(Node c) {
    Node p;  // left child of c

    p = c.left;
    c.left = p.right;
    p.right = c; = Math.max(height(c.left), height(c.right)) + 1; = Math.max(height(p.left), height(p.right)) + 1;

    return p;

static public Node rotatewithright(Node c) {
    Node p;  // right child of c

    p = c.right;
    c.right = p.left;
    p.left = c; = Math.max(height(c.left), height(c.right)) + 1; = Math.max(height(p.left), height(p.right)) + 1;

    return p;

static public Node doublerotatewithleft(Node c) {
    Node tmp;

    c.left = rotatewithright(c.left);
    tmp = rotatewithleft(c);

    return tmp;

static public Node doublerotatewithright(Node c) {
    Node tmp;

    c.right = rotatewithleft(c.right);
    tmp = rotatewithright(c);

    return tmp;

static public Node avlinsert(Node newNode, Node par) {
   Node newpar = par;  // root of subtree par

    if (newNode.val < par.val)  {
        if (par.left == null) {
            par.left = newNode;  //attach new node as leaf
    else {
         par.left = avlinsert(newNode, par.left);   // branch left
         if ((height(par.left) - height(par.right)) == 2) {
            if (newNode.val < par.left.val) {
            } else {
            } //else
         } //if
      } // else
   } // if
    else if (newNode.val > par.val) { // branch right
        if (par.right == null) {
            par.right = newNode;   // attach new node as leaf
        } else {
            par.right = avlinsert(newNode, par.right);  // branch right
            if ((height(par.right) - height(par.left)) == 2) {
                if (newNode.val > par.right.val) {
                } //if
                else {
                } //else
            } //if
        } //else
    }  // else if

    // Update the height, just in case

    if ((par.left == null) && (par.right != null)) = + 1;
    else if ((par.right == null) && (par.left != null)) = + 1;
    else = Math.max(height(par.left), height(par.right)) + 1;

    return newpar; // return new root of this subtree

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