An example Toroidal Sudoku: the grid is a torus - the right edge wraps to the left and the top to the bottom, so a region can run off one side (arrows) and continue on the other.
Toroidal Sudoku treats the grid as a torus: the right edge wraps around to the left and the top to the bottom. Jigsaw regions can run off one side and continue on the other, so a single region may span the grid's edges as if they were joined.
The rule: the grid wraps around
Rows, columns and regions all still need 1-9, but regions may wrap across the borders. Below, one region (purple) exits the right edge and re-enters on the left - the two shaded strips are the same wrapping region.
A region wrapping the edges: the cells on the right and left belong to one region across the torus.
Solving strategy
- Follow regions across the edges. A region leaving one side continues on the opposite side.
- Scan wrapping units as one. Treat the two edge strips of a wrapping region as a single region for 1-9.
- Mind the wrap on lines too. Some variants wrap the row/column logic as well - check the puzzle.
- Feed the grid. Each digit placed behaves like a given for its row, column and (wrapping) region.
Common mistakes
- Treating the edges as walls. On a torus the borders join - regions and (sometimes) lines continue across.
- Splitting a wrapping region. The edge strips are one region and share the 1-9 requirement.
- Ignoring the ordinary rules. Rows, columns and regions still need 1-9.
Can I play it here?
Not yet - Toroidal Sudoku 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 Classic, 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
Toroidal Sudoku belongs to the irregular region family and runs on 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. Expert Sudoku leaves 25 of the 81 cells filled, where the beginner tools dry up almost entirely; Evil Sudoku leaves 23, with no easy moves at all. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.