When to Use

Look for these signals in the problem:

• Hierarchical data structure given: When the problem provides a tree, traversal patterns (preorder, inorder, postorder, level-order) apply directly.
• "Subtree" in problem statement: Problems involving subtrees naturally decompose into recursive subproblems.
• BST property mentioned: Binary Search Trees enable $O(\log n)$ search by eliminating half the tree each step.
• "Path" from root or between nodes: Tree paths are found by combining paths through ancestors and descendants.
• "Depth" or "height" calculations: Recursively compute depth as $1$ plus max child depth.