It's all logic!
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 intro first. Below are the most common techniques you can use once you’ve covered the basics.
The techniques here link directly to the Sudoku Of The Day Website which has much more information available, and can be viewed on a phone or tablet, or from a desktop computer.
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
We recommend that once you've progressed on to trying the medium techniques, that you switch on the Auto Pencilmarks feature in Astraware Sudoku (it's available in the options!) to help take out some of the more manual part of the process, letting you focus on the logic part rather than just the paperwork!
Advanced 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 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!
The puzzles in Astraware Sudoku (and on the Sudoku Of The Day Website) do not require the use of Nishio or Guessing.