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 23-Mar-2018

... by: Murray Goold, Perth, West Aust

Incredible: so much info!
Your Pattern Overlay example is prob missing a 3: G2 has to be 3 coz it’s the only 3 on Row G.
Saw several typo.s but only remember 2;
Somewhere around Medusa you’ve typed:
1. “forth”, should be “fourth”
2. “vis versa”, but appears ok as “vice versa” in intro section
Thought I had an “unsolvable” from Iversoft in Apple Store, but I’m sure Loops or Chains will “solve” it - to me (at this stage) that’s not really solving, its trial-and-error.
BUT, big thanks for making this info available. NB, I’ve only just got internet (and iPhone).

Andrew Stuart writes:
Welcome to the Internet. Thanks for the typos. Believe me some very eagle eyed people have been reading these documents for over a decade (the older ones) and sending me corrections, so it still amazes me there are typos to be found, so well spotted.

Thursday 22-Mar-2018

... by: Prime97, England

Andrew like your site and i have found it most helpful and instructive. I cannot claim that I understand everything you write about but I am tackling much harder puzzles than previously. Your emphasis seems to be centred on the computer logic and I find it takes a lot of hard study for me to understand how to use it. I would like it better if it led me gently from the things to look for in starting on a technique/strategy and the method of using it manually, but your examples are a help. Your site is my preferred learning site. I would love to be able to consign Bowman's Bingo to the archive shelf.
Thank you.

Andrew Stuart writes:
Yes, you are correct in identifying a bias. To me the puzzle is how we can crack Sudoku puzzles generally rather than specific instances. I've struggled to follow the discussions and strategies on the forums (back in the day, some of these forums are sadly lost now). Partly this is because some people, clearly very clever people, were nevertheless poor at describing their ideas and I was often reduced to studying a bare example to see if/how it could be generalised and picking through the esoteric terminology. The process of documenting it at a level I could understand was part of the way to understanding it for me and that helped make an algorithm to detect all cases. I try and illustrate the scope of a strategy with exemplars and get all the variations which must come from the algorithm. Sudoku is very deep in that there are still example puzzles with bottlenecks that will never be solved with simpler strategies, that's just it's nature. Some strategies are far from pen and paper solutions and are rather academic, I agree, but one of the aims of getting them out in public is to research ways to replace them with better, simpler strategies, if that is possible. Which is why it's such an exciting puzzle to ponder.

Thursday 22-Mar-2018

... by: PP, NC, USA

Best solver I've found! I learn from it, which is the best of all for me. Thank you!

Andrew Stuart writes:

Sunday 7-Jan-2018

... by: Pete T., USA- Michigan

Still the best Solver on-line. When I get stumped I come here. When I want to learn or understand a solving strategy I come here. The only suggestion I have is to have each solved number show initially in a different color (maybe yellow) and then change to blue at the next "show possibles". It is sometimes difficult to notice all the solved squares in reviewing the board before they join the other blues. Likewise when using the 'back' button, the latest solved squares could be highlighted to highlight what just happened.
Thanks for a great solver

Andrew Stuart writes:
That’s a sound idea and you catch me in an idle moment. So refresh the solver. I've given new solved cells a blush. I can't see to do yellow since the shadow color seems to blend with the font color which is blue. Odd but otherwise ok I think
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Thank-you everyone for all your questions and contributions.