📜 WAYPOINT LESSON
Contest 3-A: Signal Chain
⭐ beginner⏳ 40 min read📍 Lesson 197 of 281
Mock contest 3, problem A: LCA path sums with binary lifting. Target: solved within 40 minutes.
Contest 3-A — Signal Chain. Node-weighted path sums: preprocess root distances and a binary-lifting table; answer = rd[u] + rd[v] - 2*rd[lca] + w[lca]. Graded near-miss: per-query parent climbing.
Contest 3-A. The wrong version produces correct answers but walks O(depth) per query — the bamboo load test buries it.