void levelOrder(Node * root) {

    queue<Node*>q;
    q.push(root);
    while(!q.empty()){
        int size = q.size(); 
        for(int i=0;i<size;i++){

          Node* popnode=q.front();
          q.pop();
          cout<<popnode->data<<" ";
          if(popnode->left!=NULL){
              q.push(popnode->left);
          }
          if(popnode->right!=NULL){
             q.push(popnode->right);
          }
        }

    }


}