void levelOrder(Node * root) { if (root == nullptr) return;

queue<Node*> q;
q.push(root);

while (!q.empty()) {
    Node* current = q.front();
    q.pop();

    cout << current->data << " ";

    if (current->left != nullptr) {
        q.push(current->left);
    }

    if (current->right != nullptr) {
        q.push(current->right);
    }
}

}