AVL Tree

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

// Structure for an AVL tree node
struct Node {
    int key;
    struct Node *left;
    struct Node *right;
    int height;
};

// Utility function to get the height of the tree
int height(struct Node *N) {
    if (N == NULL)
        return 0;
    return N->height;
}

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

// Helper function to create a new node
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);
}

// Right Rotate
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;
}

// Left Rotate
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
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;
}

// Preorder traversal to print the tree
void preOrder(struct Node *root) {
    if (root != NULL) {
        printf("%d,", root->key);
        preOrder(root->left);
        preOrder(root->right);
    }
}

int main() {
    struct Node *root = NULL;
    int num;
    char delimiter;

    // Read integers separated by comma until newline or EOF
    // Input format example: 3,1,4,6,9,2,5,7,
    while (scanf("%d", &num) == 1) {
        root = insert(root, num);
        
        // Check for the delimiter (comma)
        scanf("%c", &delimiter);
        if (delimiter == '\n') {
            break;
        }
    }

    // Print preorder traversal
    preOrder(root);
    
    return 0;
}