Solver App for Android
Strategies for Popular Number Puzzles
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Feedback and Questions

I've received a lot of interesting comments and questions from Sudoku fans over the last few years and this page is where I try to answer them. I'm also directing Str8ts feedback here. Please feel free to drop me a note on the side of the page. Or you can email me directly at .

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Many thanks to all the people who have helped improve the solvers and strategies with their feedback!

Sunday 31-Dec-2006

... by: steve brod, utah

I like doing the 4x4 grids with 0-9 and a-f options but I hate filling in all the cell options as it takes forever. Do you have an x-cel formula that will fill in the missing numbers for each cell. I like doing it by hand so I would just print it out.

Thanks for the help.

Andrew Stuart writes:

I do have a solver for 16x16 which I wrote last year - its not got all the strategies that the 9x9 have since I stopped working on it. It will give you the opening candidates if you press Take Step once. But I've just checked it again and it doesn't have a print feature. The main board doesn't really paste well into Excel either.

It shouldn't be a big task to create an excel spreadsheet with that ability.

I'll add it to the job queue, it should have been released a while ago ;-)

Saturday 30-Dec-2006

... by: Philipp, Germany

Load Sudoku:

If I try to solve this sudoku there is only found a hidden pair but then there is nothing else...
Is it impossible to solve it by logic steps?

Thursday 28-Dec-2006

... by: Sue Ogden, United States

The Jigsaw solver is very helpful as well as educational. Helps to see the various stategies in action. Could you set up another pattern for the regular Sudoko (3x3's within the 9x9)? The basic Sudoko helper doesn't go into many of the advance techniques or explanations that I found most useful in the jigsaw solver.

Andrew Stuart writes:
Not sure if you are aware of - this pretty much does what you describe. The jigsaw solver is based on the orginal normal sudoku one

Friday 22-Dec-2006

... by: Richard Proctor, US


I'm trying to get my mind around both of the "Y Wing" strategies. I've tried to understand all of your examples but I cannot seem to understand the relationships. I've seen some ot these in some of the puzzles that I've done recently. And after I felt that I knew what the possibility was I checked the answer sheet and I was right, but I don't understand why. I just see the possibility.

Can you help me better understand this strategy?


Friday 22-Dec-2006

... by: Richard Proctor, US

Do you have a date for the publication and availability of "The Logic of Sudoku" yet? I remember first hearing that it would be out around the end of November. What is the current status? Thanks.

Richard Proctor

Wednesday 20-Dec-2006

... by: Steve Powers, United States


Your Jigsaw solver is a nice tool. However, I would like to suggest that you consider changing the order of the basic tools from:

1: Singles in Row/Col
2: Singles in Box
3: Naked Pairs/Triples
4: Hidden Pairs/Triples
5: Naked Quads
6: Pointing Pairs
7: Box/Line Reduction


1: Singles in Row/Col
2: Singles in Box
3: Naked Pairs/Triples
4: Pointing Pairs
5: Box/Line Reduction
6: Naked Quads
7: Hidden Pairs/Triples

The order of revised order of 1-5 are pretty arbitrary, but I suspect that these 5 steps are used by most players to find eliminations before they ever start looking for Naked Quads or hidden pairs or triples. Without aid, I have successfully used ALL of the first 6 steps on a regular basis. Perhaps, I have RARELY found a hidden pair. I don't think that I've EVER found a hidden triple - without someone (or a program) pointing it out to me.

Saturday 16-Dec-2006

... by: Sim, Hong Kong

When I press the botton 'Take a step' for the puzzle Escargot, it just appeared the sentence 'Run out of known strategies.' after I pressed the botton for a few times.

Thursday 14-Dec-2006

... by: Karsten Nyblad, Denmark

Load Sudoku:

Assume that a sudoku contains an error. You use as condition for stopping that there are to cells containing the same value in the same row, column, or box. However, in some cases all candidates get deleted from a cell, but you never get two cells containing the same value in the same row, column, or box.

The attached sudoku has this properry.

The solver should report an error, if all candidates are deleted from a cell.

Wednesday 13-Dec-2006

... by: ken, New Jersey

It's just a small thing but I was looking at the explanation for the X Wing strategy and you refer to square "G7" but the board is only numbered for both rows and columns so there's no "G".

Sunday 10-Dec-2006

... by: DoloresB, Chicago

I love your site. But I have one problem. When I click the "go back one step " button, I go back 4 or 5 steps.

Andrew Stuart writes:
Is this occurring when you have arrived at an advanced strategy - ones with check boxes next to them? If so then these advance and go back from the X-Wing. That is the first one on the list which works is the step and its 'goes forward' to this point. If you 'go back one step' it will go back to Box/line reduction. Is this the behaviour you're describing?

Anyone else having a similar problem?

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Thank-you everyone for all your questions and contributions.