TreeNode * find_forest (vector<TreeNode*> &res, TreeNode *root,unordered_map <int , bool > &del, bool parent_del  )
    {
        if (root == nullptr)
            return nullptr;
        int cur = root -> val;
        bool deleted = del[cur];

        if (!deleted && parent_del)
        {
            res.push_back(root);
        }

        root -> left =  find_forest(res, root -> left, del,deleted);
        root -> right = find_forest(res, root -> right, del,deleted);

        return deleted ? nullptr : root;

    }
    vector<TreeNode*> delNodes(TreeNode* root, vector<int>& to_delete) {

        unordered_map <int , bool > del;
        vector<TreeNode*> res ;
        for (int i = 0 ; i < to_delete.size(); i++)
        {
            int val = to_delete[i];
            del[val] = true;
        }
        find_forest(res, root, del,true);
        return res;
    }