How To Play
Ok, so you have come this far! We will now show you techniques to get you going. The expression ‘practise makes perfect’ could have been formulated exclusively for Sudoku
Before we start, please note the following guidelines. Try not to guess. Guessing is only required in a small percentage of cases, most particular when solving very difficult puzzles. As a rule, save yourself the heartache of guessing just to unpick your path shortly afterwards! ?
Use a pencil, pen and eraser (aka rubber) to solve the puzzle. Pencil in the values if you are not sure. An incorrect entry can be erased if you realise your mistake later on. If you are sure about a particular value, you may enter the value in pen. This way you will also keep track as to which cells require your attention.
Lets go, you know what must be achieved. The following puzzle will be used throughout this lesson. We will focus on certain parts of it to emphasize certain techniques.
Lets look at the top band (first three rows) ... we must start somewhere! - Image 1
Image 1 (before)
Image 1 (after)
We ignored number 1 as it couldn’t be solved by using crosshatching. There is no sequence, you may start with any number and change to any other number whenever you wish, as long as it helps you to make progress.
We can use crosshatching in columns as well. - Image 2
Image 2 (before)
Image 2 (after)
Try and solve number 5 in column 3 before we move on to the next technique.
Slicing and Dicing
It’s similar to crosshatching, except we are going to look at the rows and columns that run through a particular box. - Image 3
Another example of slicing and dicing is to find the 4 in box 6. - Image 4
At this stage, and anytime in between, you may revert back to just using crosshatching again. You should also revisit cells that couldn’t be solved previously because the new numbers that you have entered makes it quite obvious which values they should get now.
Back to simple crosshatching ... we are looking for a 3 in box 4. - Image 5
And some more slicing and dicing just for good measure! Where would you enter a 3 in box 9? - Image 6
So far so good!!! The bad news, however, is that you might get stuck using only these two techniques. But then we just jump to a new technique called penciling in. We have entered all the candidates (possible values) for each cell in box 5. - Image 7
When there is only one candidate in a cell, that number becomes the value for that cell. In our example there are two cells in box 5 with single candidates ie 2 (r6c4) and 9 (r6c5). - Image 8
You will notice [and this is important] that we have eliminated the 9 from its other two possible cells because a box can only have one 9. Our next rule states that when a candidate appears just once in a unit (a box in this case) that number goes into the cell. In our example, the number 7 does not appear anywhere else, so we can enter it in r5c5.
Unfortunately this leaves us with two cells, both with two candidates, and we cannot make any further progress ... for now at least.
Looking at row 4 now, we can work out what number must be entered in r4c7 based on the rule that every row must contain the number 1 to 9. You actually don’t need any fancy techniques to enter 9 there, do you? - Image 9
Box 4 produced an excellent example of slicing and dicing for the number 8. - Image 10
Try now to enter the numbers we have higlighted using the techniques covered so far. The small numbers in the cells represent the suggested sequence in which you should complete them. - Image 11
After you have finished we will use penciling in box 1 to 3 again. - Image 12
Two cells produced just one candidate each ie 8 (r2c1) and 5 (r3c7). - Image 13
Looking at box 3 you will notice that the number 1 only appears in one cell as a possible candidate. Therefore, 1 can be entered as the value for r1c7. As a result the number 6 (same box) now only appears as a candidate for one cell ie r1c8. Each box must have its own 6, therefore 6 can be entered as the value in that cell.
In box 2 there is a lonely 3 (r3c5). - Image 13
Well folk, we are sure you will now be able to finish the rest of this puzzle quickly. You may click on the serial number if you wish to view the solution. There are a lot more other tips and tricks available, which we will share with you in future.
That brings us to the end of our How to Play tutorial. If this was your first encounter with a Sudoku puzzle, we recon you should be able to get going now. We have a link on the FAQ page to more advanced techniques which is well worth the visit if you wish to do more difficult Sudoku puzzles.