AVLTree.C

#include <stdio.h>
#include <stdlib.h>

// An AVL tree node
struct Node
{
    int key;
    struct Node *left;
    struct Node *right;
    int height;
};

// A utility function to get the height of the tree
int height(struct Node *N)
{
    int lh, rh;
    if (N == NULL)
        return 0;
    else
    {
        lh = height(N->left);
        rh = height(N->right);
        if (lh > rh)
        {
            return (lh + 1);
        }
        else
        {
            return (rh + 1);
        }
    }
}

// A utility function to get maximum of two integers
int max(int a, int b)
{
    return (a > b) ? a : b;
}

/* Helper function that allocates a new node with the given key and
    NULL left and right pointers. */
struct Node *newNode(int key)
{
    struct Node *node = (struct Node *)
        malloc(sizeof(struct Node));
    node->key = key;
    node->left = NULL;
    node->right = NULL;
    node->height = 1; // new node is initially added at leaf
    return (node);
}

// A utility function to right rotate subtree rooted with y
// See the diagram given above.
struct Node *rightRotate(struct Node *y)
{
    struct Node *x = y->left;
    struct Node *T2 = x->right;

    // Perform rotation
    x->right = y;
    y->left = T2;

    // Update heights
    y->height = max(height(y->left),
                    height(y->right)) +
                1;
    x->height = max(height(x->left),
                    height(x->right)) +
                1;

    // Return new root
    return x;
}

// A utility function to left rotate subtree rooted with x
// See the diagram given above.
struct Node *leftRotate(struct Node *x)
{
    struct Node *y = x->right;
    struct Node *T2 = y->left;

    // Perform rotation
    y->left = x;
    x->right = T2;

    //  Update heights
    x->height = max(height(x->left),
                    height(x->right)) +
                1;
    y->height = max(height(y->left),
                    height(y->right)) +
                1;

    // Return new root
    return y;
}

// Get Balance factor of node N
int getBalance(struct Node *N)
{
    if (N == NULL)
        return 0;
    return height(N->left) - height(N->right);
}

// Recursive function to insert a key in the subtree rooted
// with node and returns the new root of the subtree.
struct Node *insert(struct Node *node, int key)
{
    /* 1.  Perform the normal BST insertion */
    if (node == NULL)
        return (newNode(key));

    if (key < node->key)
        node->left = insert(node->left, key);
    else if (key > node->key)
        node->right = insert(node->right, key);
    else // Equal keys are not allowed in BST
        return node;

    /* 2. Update height of this ancestor node */
    node->height = 1 + max(height(node->left),
                           height(node->right));

    /* 3. Get the balance factor of this ancestor
          node to check whether this node became
          unbalanced */
    int balance = getBalance(node);

    // If this node becomes unbalanced, then
    // there are 4 cases

    // Left Left Case
    if (balance > 1 && key < node->left->key)
        return rightRotate(node);

    // Right Right Case
    if (balance < -1 && key > node->right->key)
        return leftRotate(node);

    // Left Right Case
    if (balance > 1 && key > node->left->key)
    {
        node->left = leftRotate(node->left);
        return rightRotate(node);
    }

    // Right Left Case
    if (balance < -1 && key < node->right->key)
    {
        node->right = rightRotate(node->right);
        return leftRotate(node);
    }

    /* return the (unchanged) node pointer */
    return node;
}

// A utility function to print preorder traversal
// of the tree.
// The function also prints height of every node
void preOrder(struct Node *root)
{
    if (root != NULL)
    {
        printf("%d ", root->key);
        preOrder(root->left);
        preOrder(root->right);
    }
}

/* Driver program to test above function*/
int main()
{
    struct Node *root = NULL;
    int num, opt;
    do
    {
        printf("\nEnter option number: 1. Add element\t2. Stop adding\n");
        scanf("%d", &opt);
        if (opt == 1)
        {
            printf("\nEnter number:");
            scanf("%d", &num);
            root = insert(root, num);
        }
    } while (opt != 0);
    printf("Preorder traversal of the constructed AVL tree is: \n");
    preOrder(root);

    return 0;
}