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Strategies for Number Puzzles of all kinds
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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. Please feel free to drop me a note on the side of the page or try the Facebook comment box. 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 3-Jul-2015

... by: Linda, Australia

I have been using your program for many years and I love it as I have learnt so much. However, the last 2 puzzles I have been trying to solve have become stuck on " 'wait ". I don't understand whether there is a problem with the puzzles or with the program. Any suggestions ?

Andrew Stuart writes (4-Jul-2015):

I'm hoping this is just the updated pages I posted to take the solver to 2.02. If you still see 2.01 on the solver then fresh a few times (F5) or clear your cache. Always happens, its just not possible to invisibly update under peoples feet with this internet stuff

Let me know is that doesn't solver it

Friday 3-Jul-2015

... by: Dave Conway, USA

Can't seem to get Jigsaw solver and Killer Solver to update to 2.02. I've tried refreshing and clearing the cache. Neither seems to work. Sudoku Solver updated.

Andrew Stuart writes (4-Jul-2015):

Very sorry to confuse you, my bad. The update doesn’t effect Killer but since they share a common core engine I should have remembered to increment the version number everywhere. Done so now, working again for me. Once F5 refresh should do it – should say 2.02 now

Thursday 25-Jun-2015

... by: rec, USA

I have been trying to use your app on a Samsung S4 and have the following observations:

When I solve a particular cell by removing all but the correct value and then activate "next step" the app does not remove the candidate entries that are no longer valid. This results in my having to manually remove these candidates. This is inconsistent with your solver on the web.

Please correct this.


Andrew Stuart writes (4-Jul-2015):

I've looked at the app and it does remove candidates if you press take step a few times. But I think you are talking about a "player mode" as opposed to a "solver mode". I am thinking about how to add that but it's not very easy as the candidates are incompatible, one has to be manually editing candidates as opposed to allow the solver to remove them. I agree that in "player mode" the candidates can be removed automatically. I am about to release version 1.74 today which contains some improvements, including a LONG click on the numbers - which inserts the big number instead of a candidate. This means its one "take step" to clear. On your main point I'll develop further and see if I can add "player" mode.

Sunday 7-Jun-2015

... by: Keith, Brisbane Aust

Thanks Andrew for a great web site. Gave me great peace of mind to discover the puzzle I was puzzling over was only solved by guessing.

Andrew Stuart writes (11-Jun-2015):

Very happy it's been helpful, your most welcome

Monday 25-May-2015

... by: Carol, Victoria BC, Canada

Happy Birthday, Andrew!! And thank you for all you offer on this wonderful site. CM

Andrew Stuart writes (30-May-2015):

Thanks Carol !

Sunday 24-May-2015

... by: Robert Messer, BC, Canada

Load Sudoku:

I am trying to understand the 3D Medusa rules. Things were going fine until I attempted the attached puzzle. Apparently, there is something I don't understand as there seems to be a contradiction to the basic colouring logic. If I have typed the puzzle in correctly, there should be bi-value cells at J7 (69), another at E7 (36) and E3 (68). If I link these 3 cells the colours of 6's at J7 and E3 should be the same. A peek at the answer key says the 6 at J7 is a solution but the 6 at E3 is not. What am I not understanding about Medusa logic?

Andrew Stuart writes (30-May-2015):

You are trying to connect cells on a value X where there are more than two X in the row or column. Say J7 was 6, yes you can turn of 6 in E7 - cos you have to turn off ALL 6s in the columns. But -6 in E7 does not imply +6 in E3 - because there are other 6s in the row.

The only way you can skip over clusters of X using bi-value cells is if ther bi-value cells contain the same numbers, eg Remote Pairs. Check the second half of X Cycles

Thursday 21-May-2015

... by: John Gallagher, Seal Beach, CA

Andrew, When I have to use "Bowman's Bingo" to solve a puzzle, It feels like I am simply guessing as opposed to actually solving.
What are your thoughts on this?

John Gallagher

Andrew Stuart writes (30-May-2015):

I agree, it is more or less equivalent to guessing. Back in the day, there were quite a few entertaining ideas about how to guess "methodically" and this was one of them. I happened to implement it as it was an algorithm I could grasp (more or less) and could have led somewhere. I do have it under the "trial and error" label on the site.

Fortunately you can keep strategies turned off now (with cookies enabled)

Wednesday 20-May-2015

... by: Peter, Indonesia

Load Sudoku:

I love your solver. I've used it for several years primarily to improve my skill at identifying chains and loops. Thank you for the effort you make in providing such an excellent tool. I solved the above puzze using the bivalue universal grave (BUG) rule which I'm sure you've seen before. Out of curiosity, I entered in into your solver to see what happens. At the point where the BUG appears, the solver identifies two XY chains that solve the puzzle. So it is only one extra step. As I'm sure you know, the BUG rule always solves the puzzle in one step when it applies. However, I would say it appears in fewer than 1% of all puzzles. Despite its rarity, have you considered adding it to the solver? The logical place for it would be as the final tough strategy following XYZ wing.

Andrew Stuart writes (30-May-2015):

I currently don’t have BUG, but I'm interested in adding it. I did have a special instance of BUG way back at the start but I knew it was not a generalised enough and what with one thing and another, I lost the original discussion of it. In 2010 I removed it from the solver as it was quite useless. Still have the docs page though. If you can describe the principle to me I can have another go, been annoying me this for some time

Wednesday 20-May-2015

... by: stripey, England

I love this site!
Is there any chance that the book will be published again, even as a paid download? It's very tantalising knowing that it exists but that I can't get hold of it!

Andrew Stuart writes (13-Jun-2015):

Yes I do hope to release a eBook version. I could export the site documentation quite easily but I think a purchaser would expect more than that. I do have several discussive chapters ready which will form the start of the book, but overall I want to include new examples. The the problem becomes one of proof checking, which is a night mare considering how problematic the paper book was. At least I could update a e-version. So it’s a bigger job that it seems but I do want to do it.

Saturday 16-May-2015

... by: jerry, georgia, usa

I do not understand your explanation on pointing pairs/pointing triples. In the example on the website there are 3s in B7 and B9 and you show that the 3s in B1, B2, and B3 can be eliminated. Why do you point left? According to the explanation is it not also possible you have pointing triplets of 3s (B1, B3, B3) that would point right. I would appreciate any additional explanation.


Andrew Stuart writes (13-Jun-2015):

The 3s in C2 and C3 prevent the other 3s in B123 from pointing.
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