Forest Roots After Removing Selected Tree Nodes

### Problem Remove every node whose value is listed in to_delete from the binary tree. The surviving nodes and their surviving edges form a forest. Return the roots of its trees in any order, using the original native node objects. ```cpp class Solution { public: vector<TreeNode*> delNodes(TreeNode* root, vector<int>& to_delete); }; ``` ### Examples **Example 1:** ```text Input: root = [4,2,6,1,3], to_delete = [2] Output: forest = [[4,null,6],[1],[3]] Explanation: Removing2 separates its children1 and3 from the surviving root4. ``` **Example 2:** ```text Input: root = [7], to_delete = [7] Output: [] Explanation: No node survives. ``` ### Constraints - The tree has at most 1000 nodes; the source states no positive lower bound. - Original node values are distinct integers in `[1,1000]`. - The deletion list has at most 1000 distinct values, each in `[1,1000]`. ### Contract considerations Retain `TreeNode*` input and `vector<TreeNode*>` output. Cut links on the existing surviving nodes; array notation only illustrates tree values. ```hint Read the boundary condition What should the forest contain when every original node is removed, or when no listed value occurs? ``` ### What a Strong Answer Covers Retain `TreeNode*` input and `vector<TreeNode*>` output. Cut links on the existing surviving nodes; array notation only illustrates tree values. ### Follow-up Questions Optional practice extension, separate from the original task: How would you report the number of nodes in each surviving component?