void levelOrder(Node * root) {
        queue<Node*> q;
        if(root == NULL)return;
        q.push(root); // add root to queue
        while(!q.empty()){
            for(int i=0; i<q.size(); i++){
                Node* tempN = q.front();
                cout << tempN->data << " "; // if you want to store you can do push_back here
                q.pop();
                if(tempN->left != NULL)q.push(tempN->left);
                if(tempN->right != NULL)q.push(tempN->right);
            }
        }
    }