📜 WAYPOINT LESSON
Checkpoint — Read, Then Decide
⭐⭐⭐ advanced⏳ 20 min read📍 Lesson 252 of 281
The first real task: static range sums at full scale. The correct complexity is decided by the constraints, not by the story.
Điểm kiểm tra — Đọc, rồi quyết định. Given n ≤ 200000 integers and q ≤ 200000 queries (l, r): compute each range sum, then report XOR of the sums and their total modulo 1e9+7. The array never changes. A per-query loop will not survive the largest test — the constraint table from this module names the tool.