You practiced recognizing which tree technique fits each problem:
• Subordinates: Simple subtree DP. One DFS, count sizes.
• Tree Diameter: Two approaches. Double BFS or DP tracking max depths.
• Tree Matching: Subtree DP with states. Track whether node is matched.
• Tree Distances II: Rerooting. Compute for one root, then shift answers.
• Choosing Capital: Rerooting with directed edges. Track reversal cost changes.
• Max White Subtree: Combine subtree DP with rerooting for global answers.
The core skill: read the problem, identify what's being asked (subtree values, global values, all-roots answers), then pick the right technique.