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 24-Dec-2018

... by: Billy, Los Angeles

Andrew, Can you make your Archive of just the 'extreme' puzzles available. Extreme puzzles on other sites are way too easy. Fortunately, I have reached a point where 90+ % of the time diabolical puzzles are also too easy.
Your puzzles are very well rated, probably the best rating I have seen, and I have been doing sudokus for perhaps 15 years.

Andrew Stuart writes:
Thanks for the kind words, appreciated. I do have a lot of stock, for sure, been going so long. (I was going to send you some extremes but you didn't leave an email address!)
There are extreme puzzles available here:

It's a delicate balance deciding how much content to provide for free and how much to charge for, especially when free is available elsewhere. I'm thinking I should really build some kind of subscription system.

Have a great new year

Saturday 22-Dec-2018

... by: Ed, N Y

Have spent many hours enjoying your jigsaw sudoku but recently had to up my browser to Mojove. Every time Mojove goes to sleep when I wake it up any live info I have on the page is erased and the page starts fresh. None of the other pages lose their live info at wake up. Someplace there is a conflict between Mojove and your web page. Any help would be appreciated, thanks, Ed

Andrew Stuart writes:
That's a difficult one. The solver page re-writes a cookie every time something changes. This contains the board numbers including current candidates and only a very few settings. It's a very ordinary sort of cookie. Mojove is presuming to ignore this on wake up. You'd have to delve into the settings for the browser. Maybe install a second browser like Firefox?

Thursday 20-Dec-2018

... by: elias, Valencia, Spain

why don't you include the ALIGNED PAIR EXCLUSION inter the easiest strategies?. It's very intuitive
Why don't you have the strategy TWO STRING KITE?

Andrew Stuart writes:
I would like to give the user the ability to sort the strategies. It is not an easy user interface feature to create, especially as the UI is already quite complex. But it is something I want to do.
I have not heard of Two String Kite. Do you have some help pages or reference?

Friday 14-Dec-2018

... by: 1equals2, Sweden

4000 sudokus! Way to go!
Thank you for the great sudoku portal!

Andrew Stuart writes:
Thanks! Can't wait for 9000!!

Thursday 9-Aug-2018

... by: St8fan, Michigan, USA

Thank God for this websire, and wifi on overseas flights! Your hints on extreme+ are awesome

Andrew Stuart writes:
Glad to be of service!
Hope you're landing somewhere fun

Monday 30-Jul-2018

... by: Norris Barnes, US

I am at a mid-point solving an extreme puzzle and I want to skip ahead to 3D Medusa to help me solve it. I complete the puzzle but find I have an error. In reviewing your solution I see that 3D Medusa was not used to solve the puzzle.

Do I have to step thru each strategy in sequence to successfully complete the puzzle?

Andrew Stuart writes:
There are numerous possible ways to solve any single puzzle and your choices are just as valid. As I wrote before, basic ones must come first but other than that, your choice. You have to step through each step but the solver will skip ahead to the first to si

Monday 30-Jul-2018

... by: Norris Barnes, us

I there a 'required' sequence of strategies to solve each Sudoku? For example, I am working on an Extreme puzzle and I get to a mid-way point where I need to work thru the strategies one at a time in the sequence you have presented BUT am I allowed to skip ahead to a strategy (e.g., 3D MEDUSA) instead of working thru each logical test?

Love your site - use frequently, much to my wife's chagrin !

Andrew Stuart writes:
No you dont need to try the lost in order except for basic strategies, whihc should be exhausted before moving to anything higher. Within basic strats these can be looked for en mass or in a different order but I think as listed then are in a natural order of complexity. There is a lot of overlap between more advanced strategies and it is difficult to order them in terms of complexity - so my ordering is my best subjective ordering. You can skip some by turning them off. I've wondered about allowing the user to re-order them but it's a complex UI problem, not a sudoku strategy problem.

Thursday 5-Jul-2018

... by: david, south america

The board has stopped working. numbers entered on the small board no longer appear on the large board. when ''take step'' is pressed the following message appears: put some numbers in the small box first

Andrew Stuart writes:
Very sorry! Made a change yesterday and didn't check all probably browsers.
[CRTL]+[F5] to refresh the page now

Thursday 24-May-2018

... by: Alfredo Trotta, Italy

Hey Andrew, sorry if a keep stalkering you, but since I discovered your site (very recently), together with your app (android in my case), the meaning of solving sudoku puzzles changed completely for me. I am really delighted in learning techniques one by one and being able to solve puzzles I never dreamt I could before.
What I find someway very difficult is understanding how can I better use the solver in helping me find the way by myself (without using the "take step" capability), in case techniques like x-cycles, xy-chain or 3d medusa should be used. Using the "candidates can be chained" option (with 3D functionality when needed), and the show bilocation links tool, the situation gets very confused and it is very difficult to spot the solution.
Is there something I am missing?
What I think could help very much would be developing a tool for highlighting specific candidates in green or red and following the chain manually from a cell to another, with the tool creating automatically the relevant link, discriminating if strong or weak.
That would be great!!!
Do you think it would be possible in the next future?
Waiting for your feedback
Thanks for your great job

Andrew Stuart writes:
I get where you are coming from. Searching for a *any*pattern in the blizzard of numbers is difficult just with pen, paper and eyeball. I started this project hoping there would be simpler strategies (but still not trial and error) and was surprised, that in the difficult puzzles those I've documented really are the best solutions. I'm certain that few newspaper puzzles rarely have the need for them and we compilers have to look very hard for hard puzzles (the distribution is weighted to easy by a long way). The site tries to record all valid approaches even ones that are very academic (that is ones that are best handled by a computer) but I do get some people claiming they solve with these methods by hand. I don't know, is the short answer. I can see that some better tools on the solver and in the app could help. But I'd need a very detailed description of how a person would use them as I don't solve individual puzzles in the same way. My work is generalizing from a strategy to find algorithms that work across many puzzles.
The other problem is space. The app doesn't really have the space to fiddle with candidates. I could try a zoom or make it tablet only. I'll take a look at candidate highlighting and links in the next version then.

Sunday 20-May-2018

... by: , Italy

Hei Andrew, why don't you add the little tool to show chains to the android app also?

Andrew Stuart writes:
I will attempt to do that next version
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Thank-you everyone for all your questions and contributions.