Between Lines Sudoku
Digits on a line must fall strictly between the two endpoint values
Easy
Between Lines Sudoku Easy
Medium
Between Lines Sudoku Medium
Hard
Between Lines Sudoku Hard
Expert
Between Lines Sudoku Expert
What is Between Lines Sudoku?
Between Lines Sudoku draws lines with circular endpoints. Every digit along the line (excluding the endpoints themselves) must be strictly greater than the smaller endpoint and strictly less than the larger endpoint. If the endpoints are 2 and 8, every middle cell on the line must be one of 3, 4, 5, 6, or 7. The closer the endpoints are in value, the more constrained the middle cells.
At a Glance
| Constraint type | Line Constraints |
| Typical givens | 20–28 |
| Difficulty rating | ★★★☆☆ 3/5 |
| Avg. solve time — Easy | 8 min |
| Avg. solve time — Medium | 18 min |
| Avg. solve time — Hard | 36 min |
| Avg. solve time — Expert | 64 min |
How to Solve Between Lines Sudoku
| Technique | What it does | Level |
|---|---|---|
| Endpoint Gap Analysis | The gap between endpoint values must be large enough to accommodate all middle cells. If endpoints are 2 and 8, middle cells must come from {3,4,5,6,7}. | Beginner |
| Endpoint Ordering | The endpoint values have no fixed order — the constraint is that all middle cells are strictly between the minimum and maximum endpoint. | Beginner |
| Tight Endpoint Constraint | If endpoints would be consecutive (e.g., 3 and 4), no middle cell could satisfy the strict inequalities — use this to force endpoints apart. | Intermediate |
| Between-Line–Box Interaction | All middle cells sharing a box must satisfy the between constraint. Use the box to eliminate candidates outside the valid range. | Advanced |
Average Solve Times
Easy
8 min
Medium
18 min
Hard
36 min
Expert
64 min
Frequently Asked Questions
Are the endpoints included in the range?
No — middle cells must be strictly greater than the lower endpoint and strictly less than the upper endpoint.
Can the two endpoints be equal?
No — equal endpoints leave no valid middle cell values. Our puzzles guarantee distinct endpoint values.