Play Jigsaw Sudoku Online
Sudoku with irregular regions — fill the 9×9 grid so every row, column, and jigsaw-shaped region contains the digits 1–9. 4 difficulty levels, notes, undo & error checking — all free.
Created by Brian Hamilton
Select a cell and enter a number
How to play Jigsaw Sudoku
Fill the grid so that every row, every column and every irregular region holds the digits 1 to 9 exactly once.
- The nine regions replace the usual 3×3 boxes. Each still holds nine squares, but the shapes are irregular and differ every game.
- Rows and columns behave exactly as in ordinary Sudoku.
- Grey digits are given and cannot be changed.
- Every puzzle has exactly one solution and never needs a guess.
Controls: tap a square and type or tap a digit. Notes lets you pencil in candidates, Check highlights mistakes and Hint reveals one square.
A region is almost never box-shaped
Jigsaw Sudoku swaps the nine 3×3 boxes for nine irregular regions of nine squares. That sounds like a cosmetic change. It is not, and the reason is worth measuring rather than asserting.
A 3×3 box always covers exactly three rows and three columns. A jigsaw region is any connected shape of nine squares, so it can stretch much further — and it usually does.
| Rows covered | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|
| Regions | 12 | 21 | 20 | 19 | 11 | 4 | 3 |
Of those 90 regions, exactly one happened to fit inside a 3×3 footprint — about 1%. Regions stretching across five, six or even eight rows are ordinary.
That is the whole difference. In ordinary Sudoku a box overlaps each of three rows by exactly three squares, and that regularity is what most solving habits are built on. Here the overlap between a region and a row can be anything from one square to nine, and it differs for every region on the board.
The technique this creates: leftovers
Because regions and rows no longer line up neatly, a technique appears that has no equivalent in ordinary Sudoku.
Take any set of rows — say the top three. Those 27 squares must hold each digit exactly three times. Now take the regions that overlap those rows. Together those regions also hold each digit exactly once per region. The squares that belong to those regions but lie outside the three rows must therefore contain exactly the digits the rows have “borrowed”.
In practice: if the regions touching your three rows spill over by four squares, those four squares hold a known multiset of digits, even though you have no idea which is which. That is frequently enough to eliminate a candidate somewhere else entirely.
The same argument works with columns, and with any number of lines. It is worth trying whenever the ordinary eliminations dry up.
A worked board
Notice where the givens cluster. Because the regions are uneven, some carry five or six starting digits and others carry one — which is itself a clue about where to work.
Where solvers get stuck
Scanning as if the regions were boxes. The habit of checking “which three rows does this box touch” simply does not transfer. Follow the region's outline with your eye each time; assuming its shape is the commonest mistake.
Missing that a region can dominate a row. A region overlapping one row by five or six squares nearly determines that row between them. Those are the pairings worth hunting for, and they never occur in ordinary Sudoku.
Forgetting rows and columns still work normally. Only the third constraint changed. Plain row and column eliminations still solve a good part of every board, and it is easy to over-focus on the unfamiliar shapes.
Two things you can check about these puzzles
Every puzzle has exactly one solution, and it cannot be otherwise. A board starts as a completely filled grid, and digits are removed one at a time — each removal kept only if a solver confirms a single solution still remains, and put straight back otherwise. Because no step that would create a second answer is ever accepted, ambiguity cannot appear.
Difficulty is the number of givens, and the regions do not change. The generator leaves about 40 of the 81 squares on Easy, 33 on Medium, 28 on Hard and 25 on Expert. The region shapes are drawn the same way at every setting, so a hard board is not a more contorted jigsaw — just the same kind of jigsaw with less to go on.
Jigsaw Sudoku, Irregular Sudoku and Nonomino
The puzzle appears as Jigsaw Sudoku, Irregular Sudoku, Nonomino Sudoku (a nonomino being a nine-square shape), Geometry Number Place and Squiggly Sudoku.
It is Sudoku with one rule swapped rather than added, which makes it a gentler jump than Killer Sudoku — there is no new arithmetic to learn, only a new shape to see.
More sudoku variants
If you like the grid with its rules bent, try these: