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📜 WAYPOINT LESSON

Contest 4-A: Watchtower Coverage

⭐ beginner⏳ 40 min read📍 Lesson 199 of 281

Mock contest 4, problem A: per-node subtree depth via one postorder. Target: solved within 40 minutes.

Contest 4-A — Watchtower Coverage. dp[v] = 1 + max(dp[child]); single iterative postorder over up to 200000 nodes. Graded near-miss: global height printed for every node.

Contest 4-A. The wrong invariant — "every node sees the tree's height" — survives symmetric tests and dies on any asymmetric star.