Binary Trees Checkpoint

1. What should a tree recursion function return for a nil node?

A base case value (e.g., 0 for depth) An error The parent node nil

2. Which traversal visits nodes in sorted order for a BST?

Inorder Preorder Postorder Level-order

3. The naive BST validation (check left.val < root.val < right.val) is wrong because:

4. In LCA, if both left and right recursive calls return non-null:

Current node is the LCA Return left result Return right result Return nil

5. Time complexity of visiting all n nodes in a tree?