You have learned four tree techniques: basic traversal, diameter, subtree DP, and rerooting. Each solves different problem types. Traversal collects data. Diameter finds longest paths. Subtree DP makes decisions. Rerooting answers for all roots.
In this section, you will practice recognizing which technique fits which problem. I'll give you six problems from CSES and Codeforces. You will think first, answer decision questions, then see the solution and implement.
By the end, you will know when to use each technique without guessing. Pattern recognition is what separates beginners from fast problem solvers.
