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!

Monday 19-Jan-2015

... by: Arkis, USA

Perhaps I've missed it. How do you delete puzzles from the "favorites" list, or the dailty puzzels list ? Want to limit storrage size.

Andrew Stuart writes:
If you are talking about the Sudoku Solver for Android, go to settings and change the choice for "how long to keep".
On favourites - long click will offer a delete

Best regards

Saturday 10-Jan-2015

... by: 0t0, europe

I've seen a bug on the Str8ts solver: When I click "Take Step", then appears a window: Oops - you've got an error on the board.

Andrew Stuart writes:
Please use the "Email this board" button to share the puzzle in question. Can't help much otherwise. The solver has been stable for some time so I've not received any other bug reports.

Friday 2-Jan-2015

... by: seventeener, europe

kakuro solver???

Andrew Stuart writes:
Kakuro is a nice puzzle, one I make. But there's not much strategy to Kakuro, it's pretty much combination elimination all the way. I've thought about it but I'd like to get more newspapers taking the puzzle before I put the time into it. Happy to be pointed at examples that are interesting though.

Thursday 1-Jan-2015

... by: oldgirl, Ontario,Canada

I really enjoy the "killer" solver, but I've noticed that it doesn't recalculate possibilities for cages when one of the values isfilled in. For example, a 3-block cage, value 20, with a 7 filled in in one block. The solver doesn't recalculate for a 2-block total of 13. I don't think that would be considered a bug, but it might prevent the solver from "running out if known strategies"

Andrew Stuart writes:
That's an interesting idea. On one level I have to preserve the puzzle as it's entered, so the small grid will always show the cage clues and combinations of the original puzzle. But I see it would be helpful to show the reduced cages. No sure what would happen if a solution was in the middle of a 3-cage - wouldn't be valid to split into three singles. Internally the solver is aware of the reduced number of combinations that a solution provides so I'm sure I'm getting the maximum value from the solved cells. There is much more work to be done on killers to get them to the 99.99% solvability I have with Sudoku. Currently about half of the hardest grade killers it still gets stuck on.

Thursday 1-Jan-2015

... by: Buzz, Usa

Hi Andrew

Happy New Year

Why not show a digit forcing chain---like in a 3D medusa---show ALL of the changes when you turn a digit ON and OFF ?

Using your DFC info---you only see one or a few changes---but---often--many are possible!

What say you?

Andrew Stuart writes:
I think what you're talking about is a Forcing Net. I've yet to explore/implement those, but in searching for a Forcing Chain I'm following all the paths that a net would. One of the problems is visual - it would be very hard to cope larger Nets unless there was some artificial limit. Forcing Chains and Nets are frowned upon by some theorists as they smack of 'trial and error' - they are one base off from being purely "state deterministic", so I'm hoping there will be alternatives before they are required. But if you can use them to solve a puzzle that’s a perfectly valid way to go
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Thank-you everyone for all your questions and contributions.