An example Twodoku: two 9×9 grids (blue, green) overlap in one shared 3×3 box (purple), shown here as a box-level schematic.
Twodoku (also Double Doku) joins two full 9×9 Sudoku grids that overlap in one shared 3×3 box. Each grid is solved under normal rules, and the shared box must satisfy both at once - so a digit placed in the overlap counts for two grids and links them together.
The rule: two grids, one shared box
The two grids sit corner to corner, sharing a single box. Every row, column and box of both grids holds 1-9; the overlap box (purple above) belongs to both. Solving one grid feeds the other through that shared corner.
Solving strategy
- Work the overlap hard. The shared box is constrained by both grids, so it usually resolves first.
- Pass digits across. A value fixed in one grid's overlap box is a given for the other grid.
- Otherwise, solve each grid normally. Away from the overlap, it is ordinary Sudoku.
- Alternate. Progress in one grid opens the other through the shared corner.
Common mistakes
- Treating the overlap as one grid's. The shared box must satisfy both grids simultaneously.
- Forgetting to transfer. A digit placed in the overlap instantly constrains the other grid.
- Ignoring the ordinary rules. Each grid still needs 1-9 per row, column and box.
Can I play it here?
Not yet - Twodoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile:
- Try the closely related Samurai, which you can play right now.
- Browse all the Sudoku variants we do offer.
- Or print free puzzles from the printable PDF page.
Where to play it
Twodoku belongs to the overlapping family and runs on Two 9×9. It is not one SudokuStreak generates yet - but the deduction it trains is the deduction every Sudoku runs on.
Difficulty and type are two separate dials here: the type sets the extra rule, the level sets how much of the grid you start with. Easy Sudoku leaves 36 of the 81 cells filled, so there is always an obvious next move somewhere; Hard Sudoku leaves 26, where scanning gets you started and then leaves you stranded. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.