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!

Friday 14-Aug-2020

... by: Julian, USA

Tried solver with variable results. Hitting return after take step, then following up first to see next step in solution and also the explanation in the box below I could see the next step most of the time, the explanation after going back and forth a few times with the links offered on the right, but only sometimes. I'd been using Safari, so I tried Chrome with even worse results, i.e., just couldn't get explanations to show. Also difficult to get the solver to advance to the next step.

Andrew Stuart writes:
If the step taken is very simple, ie just clearing candidates or setting cells to be solved the "results box" will not update nor delete the contents of the last time it was updated. There should be some activity somewhere, no step is void of any change. Likewise the step you are on will be indicated if your click lands. But let me know a puzzle if you think it is and I can step through as well.

Wednesday 12-Aug-2020

... by: ART, United States

Is there a way to highlight "Show Possibles" when this step is taken?

Andrew Stuart writes:
Not really, not without adding a further step that slows things down. It's usually not a step of great interest since it is clearing from the known clues/solutions. You can use the back button and then take step again to visually see what has changed.

Tuesday 11-Aug-2020

... by: Jack, California

I enjoy your Sudoku Solver. I usually use it on 'brain dead' days when I get stuck.

As we step through the solution, I would like to have newly filled in cells displayed in an intermediate color (green?). This would make it easier to see which cells were just updated. At the next step, they could then change back to blue as the solution progresses.


Andrew Stuart writes:
I did add a colored drop shadow to the big blue numbers not very long ago, for the same request. Not powerful enough indicator?

Friday 7-Aug-2020

... by: astromath, USA

It's been a few years since I asked this, will you be adding the ability to add your own jigsaw to the jigsaw solver? I wouldn't think it would be too hard since the Killer Solver is a variant of the Jigsaw Solver but with smaller box "pieces."

BTW, the Killer Solver is also known as Sum-Doku (by Dell Magazines)

Andrew Stuart writes:
You are right, been on the job queue for too long.
Right now though I'm stuck in France and it's super hot, can barely think. But a good job for when it cools down

Wednesday 22-Apr-2020

... by: Ferdeir, Germany

Can not see any 2020 comments, 2019 ok. What's is haspenning??

Andrew Stuart writes:
Lets see if they appear now!

Hmm. Jan to March seem missing. Hope there's not been a database error

Tuesday 21-Apr-2020

... by: Frankel, USA

Cracking-the-Cryptic has just published a new theory/strategy from some one in Germany called Phistomefel. Supposedly good for any type of Sudoku. It is in a YOUTUBE video called "brand new Sudoku trick you won't believe". Might be hard to implement in your solver. Never seen it mentioned elsewhere. Have you seen it before???

Andrew Stuart writes:
Very good tip, thanks for sharing. Wow, quite an interesting insight! I'll certainly have to put a page up about this.
It should be a strategy, but there are also other configurations so it could be messy.
Nevertheless, so surprised it's taken 15 years to discover!

Wednesday 15-Apr-2020

... by: Wil, Calif., USA

This site is great.

I am trying to practice the tough strategies. Is there a way to select puzzles that only need strategies up to a certain level such as Tough strategies. I thought I could use the column heading in the daily sudoku calendar but the first one I tried in the tough column was April 8 2020 and required a diabolical strategy.

Andrew Stuart writes:
I've just gone to the Daily Sudoku page and clicked on all the April Tough puzzles using the calendar grid "Load Sudoku into Solver" and then clicked on "Grader". All came up Tough. It is possible for stocked loaded a while back to drift away from the latest solver but not really recently.

If you mean why do some puzzles have diabolical strategies that is because the strategies used is only partly what counts towards the score. Some puzzles will be easy apart from a bottle neck which doesn't push the score over the grade. I do try an filter away puzzles that are like this too much. If you want to read more about the grading there is a paper here.

Saturday 11-Apr-2020

... by: David Eide, Oregon United States.

During this stay at home pandemic I thought it would be fun to play Sudoku for two. Not that there is such a thing but Andrew is a clever man and can find a way that two people can complete a puzzle competing against each other. Of course scores and records should be kept so anyone can challenge the top players. Well, people should be rated so a No 1 is not wasting time competing against a No. 8. Thanks. Oh, please let me know when it is available.

Andrew Stuart writes:
I did toy with this idea way back in 2005 and did get some kind of 2 way player working. The tech was unreliable and clunky but that's improved since back then. I'll move it up the to-do list.

The rules I envisaged was both players could fill in any cell at any time and get a point for each correct number. Negative number for incorrect - to discourage spamming. There is an issue of deadlocking, mainly that who gets it first is down to the timing to the server.

Then there is the whole issue of managing queues of people and matching them up. Asynchronous programming is a bit of a dark art. Probably require a good but expensive developer to get it right.

Would be nice at this time, I agree.
I will keep in you in mind for testing then.
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Thank-you everyone for all your questions and contributions.