All Sudoku Variants
Two 9×9 · Overlapping

Twodoku

Also known as Double Doku, Sensei Sudoku

Two 9×9 Sudoku grids that overlap in one shared 3×3 box, each solved under normal rules at once.

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: