Introduction to Sudoku Variants

Most everyone understands the rules of Sudoku. It is a 9x9 grid that is split into 9 boxes, or regions, of the numbers 1-9, with each row and column also including the numbers 1-9. But what can a Sudoku builder use to create a more unique and challenging puzzle? There are many variants of Sudoku using various techniques to change how a solver finds the solution. Some creators will add new rules, while others will completely change the way you go about solving the puzzle.

A Sudoku variant is a rule or an addition to the grid that introduces extra strategy into the puzzle. Some popular variants include the following:

Killer Sudoku

In this variant the grid is completely empty of clues. However, within the entire grid there are irregular shaped cages that are usually outlined with a dotted line. These cages are what make Killer Sudoku Unique. Each cage has a small number indicating the sum of the squares in the cage. Killer Sudoku is commonly referred to as a combination of classic Sudoku and Kakuro.

So How Do You Make It?

Just like any regular Sudoku, you first fill a blank grid with the numbers 1-9 in each row, column, and 3x3 region. This will make up your puzzle’s solution. Next, you will begin to assign numbers to create cages. A cage will typically have anywhere from 1 to 5 different, non-repeated, numbers inside. However, you can create bigger cages with more squares if it fits into your puzzle.

Once you build your cages, you can now sum up the numbers in each of the cages and write the sum on the top-left square of each cage. After every cage has a sum, you can now take away the solution of the puzzle. It is a good idea to have someone playtest all Sudoku you create to ensure that your unique solution can be concluded.

Chess Sudoku

Chess Sudoku are actually a group of different variants, taking inspiration from different pieces in the game of Chess. These variants include Knight Sudoku, and King Sudoku. As the name implies, these variants use the moves of chess pieces as an extra constraint in the ruleset. Meaning numbers cannot be a knight's move (in an "L" shape) or king’s move (one square in any direction) away from itself.

So How Do You Make It?

If you want to use Chess logic in your Sudoku, first you will pick what kind of Chess Sudoku you will be building Knight Sudoku or King Sudoku. For my example I’ll be using Knight Sudoku. As shown above, the highlighted blue square is my number and each yellow square represents the squares that a knight can move to in a game of chess. The yellow squares cannot be the same number as the blue. When building Knight Sudoku, any square that is a Knight's move away from another square must not share the same number. Once all the numbers are appropriately placed the Knight Sudoku is complete.

As for King Sudoku, any number in a square may not be duplicated vertically, horizontally or diagonally next to that square.

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