📜 WAYPOINT LESSON
Checkpoint — Digit Sums
⭐ beginner⏳ 40 min read📍 Lesson 160 of 281
A heavy query load of exact-K digit-sum counts; the tight-flag drop that undercounts every boundary is the graded wrong answer.
Checkpoint — Digit DP. Each line: L R K (read until EOF). Print, per line, the count of x in [L, R] with digit sum exactly K.
The tight flag is the entire difficulty: dropping it undercounts.