Coding - Tree Levels After Node Deletions

The "Tree Levels After Node Deletions" problem is a coding interview question recently associated with companies like xAI and Snowflake. It is a variation of the classic "Delete Nodes and Return Forest" problem (LeetCode 1110) but often includes specific constraints or additional requirements regarding the levels or depths of the resulting forest. YouTube +3 0 1 6 2

Problem Statement Overview

You are given the root of a binary tree where each node has a unique integer ID. You are also given an array toDelete containing the IDs of nodes that must be removed from the tree. 1

Key Requirements:

• Deletion: When a node is deleted, its children (if any) become the roots of new trees, forming a forest.
• Forest Formation: You must return a list of the roots of all trees in the remaining forest.
• Level Constraint (Specific to xAI/Snowflake version): In some variations, the problem asks you to track or report the original levels of the nodes that remain or the maximum depth of the resulting forest components. YouTube +3

Example Scenario

If you have a tree where 1 is the root, 2 and 3 are its children, and you delete node 1:

1. Node 1 is removed.
2. Nodes 2 and 3 now have no parent.
3. The resulting forest contains two separate trees rooted at 2 and 3. YouTube +1

Common Solution Strategy

1. Use a Set: Convert the toDelete array into a hash set for 𝑂(1) lookup.
2. Post-Order Traversal (DFS): Use recursion to traverse the tree from bottom to top. This allows you to process a node's children before deciding if the node itself should be deleted.
3. • It is the original root and is not in the delete set.
   • Its parent was deleted and the node itself is not in the delete set.
4. It is the original root and is not in the delete set.
5. Its parent was deleted and the node itself is not in the delete set.
6. Edge Case Handling: Ensure that if a node is deleted, its parent's pointer to it is set to null to properly "detach" it from the original structure. YouTube +4

Would you like to see a Python or Java implementation for this specific tree deletion logic?

[0] - Delete Nodes And Return Forest - Leetcode 1110 - Python [1] - Tree Levels After Node Deletions | 1Point3Acres [2] - Delete Nodes And Return Forest at Meta - CodeJeet [3] - Treees – 3 [4] - Delete Nodes from a Binary Tree (Java) [5] - Reason of child node assignments after deletion from Binary ... [6] - Tree Levels After Node Deletions | 1Point3Acres [7] - Tree (abstract data type) - Wikipedia