Jigsaw Sudoku Rules: How to Play (With a Printable Example)

The Jigsaw Sudoku rules are short: fill a 9 x 9 grid with the digits 1 to 9 so that no digit repeats in any row, any column or any region. A region is a group of nine connected cells with an irregular shape, drawn with a thick line. Everything else on this page explains what that means in practice, shows a grid you can check yourself, and describes how the LogikLand generator builds the puzzles.

The three rules

1. Each of the 9 rows contains the digits 1 to 9 once.
2. Each of the 9 columns contains the digits 1 to 9 once.
3. Each of the 9 regions contains the digits 1 to 9 once.

That is the whole list. Compared with a classic Sudoku, only the third rule changes: the nine square 3 x 3 boxes are replaced by nine regions of other shapes. You never need arithmetic, and you never have to guess, because every grid has one solution.

What a region is

A region has exactly nine cells, and its cells touch each other along their sides, so it is a single piece. It may be a long snake, a staircase or a thick L. In the printed book neighbouring regions also get slightly different shades of grey, which helps you see where one ends and the next begins.

We measured the maps made by the generator: in 300 maps (2,700 regions), 86 % of the regions cover 3, 4 or 5 rows. A few regions reach all nine rows. A square 3 x 3 region does still appear now and then, 33 times in the 2,700 regions, so do not be surprised by it.

An example you can check

Check the rules on the solution with a pencil:

• Row 1 reads 3, 5, 9, 7, 6, 8, 1, 2, 4: the nine digits, once each.
• Column 1 reads 3, 7, 9, 4, 5, 8, 1, 2, 6: again the nine digits.
• The region that contains row 5, column 1 has the cells row 3 column 1, row 4 columns 1 to 3, row 5 columns 1 to 3, and row 6 columns 2 and 3. Their digits are 9, 4, 2, 7, 5, 3, 8, 6, 1: nine different digits, no repeat.

How LogikLand builds a grid

The generator works in four steps, which is why you can rely on the rules above:

1. It starts from the nine ordinary boxes and swaps one cell between two neighbouring regions, about 80 times. It refuses any swap that would cut a region in two, so every region stays in one piece.
2. It fills the grid with a complete valid solution for that map.
3. It removes digits two at a time, in symmetric pairs, as long as the solution stays unique.
4. It checks how hard the result is to solve and keeps the grid only if it matches the level you asked for.

Three common mistakes

• Looking for 3 x 3 boxes. In a Jigsaw grid the square boxes are not a rule. A 3 x 3 square that you see is just a part of the page; only the thick lines count.
• Forgetting that a region can be thin. A region may be only two cells wide and run down the page, so it can hold a digit that a nearby row already shows. Check each row against each region it crosses.
• Placing a digit by checking only the row and the column. The region is the third check, and it is the one that catches most errors when you check your own solution.

Jigsaw versus classic Sudoku

The variation in the third row is the reason Jigsaw feels different. A cell with only 16 neighbours has fewer clues around it, and a cell with 23 is easier to place.

The four levels

In a book

The Jigsaw Sudoku assistant works after you create a free account. You pick the page size (8.5 x 11 or 6 x 9 inches), one level or several, the number of puzzles, 1, 2 or 4 puzzles per page, and 1, 2, 4 or 6 solutions per page. You can choose how each title reads (name, level and number, or the number alone) and whether the rules page is a detailed guide, a short page or left out. Books on the FREE plan are for personal use; commercial rights come with the PRO and EXPERT plans.

Questions