Outside Sudoku
Digits outside the grid must appear in the first three cells of that row or column
Easy
Outside Sudoku Easy
Medium
Outside Sudoku Medium
Hard
Outside Sudoku Hard
Expert
Outside Sudoku Expert
What is Outside Sudoku?
Outside Sudoku places digits in the margins of the grid. Each outside digit must appear in one of the first three cells (the nearest box) of the row or column it points to. No standard given digits are provided inside the grid — all clues come from the margins. This creates an unusual form of Sudoku where the initial constraints come from outside the grid entirely.
At a Glance
| Constraint type | Outside Clues |
| Typical givens | 28–36 given + 4×9 outside clues |
| 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 | 65 min |
How to Solve Outside Sudoku
| Technique | What it does | Level |
|---|---|---|
| Clue-Zone Mapping | Each outside digit must appear in the nearest 3 cells of its row or column. Map all outside clues to their zones immediately. | Beginner |
| Cross-Side Reasoning | If left clue digit X must be in cols 1–3, and right clue digit X is in the same row, that row already places X — the other side confirms its column. | Intermediate |
| Box-Side Interaction | An outside clue for a row interacts with the box containing cols 1–3. If the row's box is heavily constrained, the outside digit's position may be forced. | Intermediate |
| Digit Elimination from Clues | When a clue digit is placed in the zone, eliminate it from the rest of the zone row/col using standard Sudoku logic. | Intermediate |
| Dual-Side Chains | Combine left and right clues for the same row: both digits restrict the same three columns from opposite ends, leaving the middle box fully determined. | Advanced |
Average Solve Times
Easy
8 min
Medium
18 min
Hard
36 min
Expert
65 min
Frequently Asked Questions
Where must outside digits appear?
Each outside digit must appear in one of the first three cells of the row or column it faces — the three cells in the nearest 3×3 box.
Are all outside clues independent?
No — multiple clues for the same row or column interact, often forcing specific placements.