Techniques For Solving Sudoku

Sudoku is a puzzle involving logic – no arithmetic or guessing is required! The basic idea of completing puzzles is to find cells (the small squares) where you are sure that only one value is a valid placement. If you’ve not played Sudoku before, take a look at our guide to how to start. Below are the most common techniques you can use once you’ve covered the basics.

Easy Techniques

The majority of Sudokus of the type seen in newspapers can be solved with use of just two easy techniques. Computer programs that assist players can make these kinds of puzzles very quick to solve, because they help to make it obvious where the next placement can be.

Technique 1 : Single Position
Technique 2 : Single Candidate
Pencilmarks

Many of the techniques that follow don’t actually provide you with a direct placement, but help you by allowing you to cross out one or more pencilmarks.

Medium Techniques

Going a little further, there are some extra techniques which help you to find either valid placements, or to help you to remove some of the pencilmarks. These are obviously quite tricky to manage without using pencilmarks!

Technique 3 : Candidate Line
Technique 4 : Double Pair
Technique 5 : Multi-Line

Advanced Techniques

Technique 6 : Naked Pairs/Triples
Technique 7 : Hidden Pairs/Triples

Master Techniques

Going a even further, there are some extra techniques which help you to find either valid placements, or to help you to remove some of the pencilmarks. These are obviously quite tricky to manage without using pencilmarks!

Technique 8 : X-Wing
Technique 9 : Swordfish
Technique 10 : Forcing Chains

Harder Still

So, armed with all of these potential techniques, you’ll be able to solve all possible Sudoku?
Well, maybe, maybe not.
The vast majority of puzzles don’t require the trickier techniques, but there are some which just aren’t solvable by simple logic alone, and require various forms of guessing to solve.
Some argue that guessing is a form of logic, but it does often mean a lot of erasing!

Nishio is a form of guessing, where you look for a guess causing a contradiction, meaning that you can rule it out. Going on from this, it is possible to solve entire Sudoku puzzles from guesses alone, but it can take a long time!

Technique 11 : Nishio
Technique 12 : Guessing