void def(struct Node* root,vector<int>&ans,int k);
vector<int> Kdistance(struct Node *root, int k)
{
  vector<int>ans;
  def(root,ans,k);
  return ans;
}
void def(struct Node* root,vector<int>&ans,int k)
{
    if(!root)
    return;
    if(k==0)
    ans.push_back(root->data);
    def(root->left,ans,k-1);
    def(root->right,ans,k-1);
}