Sudoku Variants Rules: How to Play (Printable Example)

Sudoku variants keep the idea of classic Sudoku and change one rule. The change is small, and it changes how you search for digits. This page explains the rules of the four variants that LogikLand makes: classic Sudoku, Sudoku X, Jigsaw Sudoku and Killer Sudoku, and shows you where each one differs, with real grids from the generators.

The rules all variants share

In all four, you fill a 9 x 9 grid with the digits 1 to 9. Every row contains each digit once, and every column contains each digit once. The variants differ in the third set of groups: classic Sudoku uses nine 3 x 3 boxes, and the others add or replace a group. You never need to guess: a grid has one solution, and logic leads to it.

Sudoku X: two diagonals

Sudoku X keeps the rows, columns and 3 x 3 boxes, and adds one rule: each of the two long diagonals also contains the digits 1 to 9 once. In the printed book the diagonals are shaded in grey so you do not forget them. The centre cell is on both diagonals, so it has to fit its row, its column, its box and both diagonals.

We checked this solution with a script: both diagonals contain 1 to 9 once, and the centre cell is an 8 on both. The puzzle has 36 digits given, the smallest number allowed at the easy level.

Jigsaw Sudoku: irregular regions

Jigsaw Sudoku keeps the rows and the columns, but replaces the nine 3 x 3 boxes with nine regions of nine cells that have irregular shapes, outlined with thick lines. Each region contains 1 to 9 once. In LogikLand the regions are different in every grid, and neighbouring regions are shaded in different greys to help you tell them apart.

The grid above has nine regions of exactly nine cells, and 23 of its 81 cells are not in the region you would expect if the boxes were square. A region that is thin and long is a good place to start, because its digits are blocked by the same few rows or columns.

Killer Sudoku: cages and sums

Killer Sudoku keeps the rows, columns and 3 x 3 boxes, gives no starting digits, and adds cages: groups of cells outlined with dotted lines, each with a sum, in which no digit repeats. The extra rule is arithmetic, which is why it asks for a different kind of attention. It has its own page: the rules of Killer Sudoku.

The four variants side by side

In the three digit-based variants the level mostly comes from how many digits are given and which techniques are needed. In Killer Sudoku it comes from the size of the cages.

Reading the table

For classic Sudoku the numbers are the digits the generator aims to leave, from 42 at the very easy level down to 22 at insane. For Sudoku X and Jigsaw they are minimums: the generator removes digits as long as the solution stays unique and the grid still needs only the techniques of its level, so a grid can have more digits than the minimum, as the Jigsaw example above does (39 digits at a minimum of 38). Killer Sudoku has no digits, so its levels are described by the size of the cages instead.

Putting them in one book

The Sudoku and Variants assistant makes a single book with one chapter per variant. A chapter starts with a title page and the rules (a detailed guide by default, a short page, or nothing), then its grids from the easiest to the hardest level. In the book, Killer Sudoku allows at most 2 grids per page; the other variants allow up to 4.

Questions