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!

Tuesday 18-Oct-2011

... by: Armand, Israel

Load Sudoku:

Hi Andrew,
Thanks for your web site, your tricks and solver.
I was stuck with a sudoku and tried to find how it was possible to finish it.
The solver gives me after few steps:
XY CHAIN length=5, 3 taken off A9, chain ends: A7 and D9
XY CHAIN length=5, 3 taken off D7, chain ends: A7 and D9
But I don't understand this chain. Is it possible to get the logic behind the scene (the chain of hypotheses) and not only the chain ends?

Andrew Stuart writes:
Have a look at the XY Chains strategy page. It should explain it fairly clearly. Yours is a good example of the technique

Saturday 15-Oct-2011

... by: Jim Holstein, USA

I have a question on example 4 on your page

on the top of the page you explain the only values you can use are where "there are only two remaining 5s left in any row, column or box". Given that LAW then why in rule 4 did you color the 4s in row B or row C which both rows have three 4s - violating the LAW?

Andrew Stuart writes:
In the diagrams on the Simple Colouring page the YELLOW candidates are being eliminated - because of the rules they illustrate. The chains are all there - between the green and blue coloured candidates.

Hope that helps!

Wednesday 5-Oct-2011

... by: Natasha, USA, California

I just wanted to say thank you so much for this solver! It really helps when you run into a puzzle that requires rough techniques that aren't fully understandable or detectable. Once again, thanks a lot!

Wednesday 28-Sep-2011

... by: Lizz, US

Hi. Great work on the solver! I've been solving jigsaws on this site for a while and every now and then I mess up; generally, I hit the wrong key and there's an error on the board. When this happens and there are two of the same number in one "block", it highlights them (very nice!) but also fills in the numbers in the diametrically opposite (if in A2/A3, also appears in B1/C1) squares and highlights them! This seems to happen on every shape, but only when the two numbers are in the same block. It will fill in the numbers even if it has to change a number that is already there. The bad thing about this is that it is difficult to recover from the error; to recover, I first have to remove one of the numbers that was wrong, then both of the numbers that were changed, and then figure out if they were empty squares or already solved!
Please fix. I really like the solver!

Andrew Stuart writes:
Fixed it! Very sorry for the confusion, it was a bug in the sanity checking routine. Very glad you pointed it out. Have fun!

Monday 26-Sep-2011

... by: Eric Holter, NC, USA

Load Sudoku:

Hi Andrew. My wife an I were flying Southwest this weekend and were doing their Spirit Magazine Sudoku (hard). I got stuck, but she finished hers (though she had to guess at one point). Oddly, her solution, which was valid, was not the one on the answer key of the magazine! I ran it through your solver to see if I had missed something and it failed to solve it (running out of known strategies). Here's a link to a PDF of the puzzle ( Any thoughts?

Andrew Stuart writes:
Interesting email and puzzle, thanks for writing in.

When you enter a puzzle in the solver it's worth while hitting the "Solution Count" button - if there is more than one solution (or zero) the puzzle is broken and can't be solved logically (hence 'run out of know strategies'). In this case there are 14 solutions - very broken. I really like examples like these, I'll have a go contacting the magazine and trying to find out who made them and how they can be so bad. It still amazes me that people will concoct any old rubbish and still manage sell it to magazines and newspapers. Wow

Monday 26-Sep-2011

... by: quaton, Perth, Western Australia

Top site!!! avid Soduku fan for many years and this is THE site to LEARN how to solve this very frustrating (at times) puzzle game....thanks Andrew

Sunday 25-Sep-2011

... by: Robert Kane, Australia

Your Sudoku Solver has just helped me solve a puzzle I was stuck on. Very impressive.

Do you sell this as an application that I can download onto my laptop (running Window 7)? I go out to remote areas of Queensland a bit with my job, to locations where I can't get internet access. This is when I get the most time to do Sudoku's. Hence, I would be keen to have something on the laptop which I can use to help me out when I get stuck.


Andrew Stuart writes:
Sorry for the late reply. I have had a windows version on the back burner for a number of years now, but my skills in that area are not up to releasing a proper version. I am working with a chap on an iphone/ipad version and I'm hoping I can reuse that to make a PC version. Keep an eye on the site for updates of that sort.

Very glad you like the site

Friday 23-Sep-2011

... by: Pete, cincinnati,oh,usa

thanks for the daily jigsaws

a few observations

the first month they were all Gentile(printable)
well im getting older and slower but i think a few extremes were slipped in...

the first two months dont necessarily copy into the solver from the daily jigsaw page( the archive ones).

i didnt look at solution archives yet.

there are some jigsaw design: (shape=) in the daily jigsaw and printable that arent in the standard shapes for the solver

it may just default to an example at the moment

Perhaps you could make the solver accept alternate shape=

Andrew Stuart writes:
A week or so ago I realised I hadn't matched the grade title on the archive calendar bits with the grades in the Jigsaw player, so I fixed that and all the links to the printable versions and the solver. It should be okay now, I'm fairly sure. I'd need a specific day to be highlighted - do let me know if you spot a mis-titled grade. With the solver I did add all the new shapes - there were five or ten or so. I realised it was important to update the solver with the new grades. Today's board is number 16 so I'll keep an eye on it and wait for a high numbers. Goes up to 28 now

That's a good idea with the shape definition. I've shied away from it since it requires the user to build something a little complex - I will need the box numbers done 1 to 9. But I'll add that feature.

Tuesday 20-Sep-2011

... by: John H., Chula Vista (San Diego), Ca

Fantastic site! Any chance this is available for Android as an app?

Andrew Stuart writes:
Soon as we're done with the iPad version, moving onto Android. Lotta demand for that platform at the moment : )

Tuesday 20-Sep-2011

... by: Larry, Georgia - USA

There is something wrong with the Jigsaw Sudoku. I have been solving the puzzles every day. It says that I have 30-40 items wrong but I cannot find any number that is incorrect.

Andrew Stuart writes:
Just now fixed, appreciate the alert. It was using the normal Sudoku boxes for checking, completely wrong!
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Thank-you everyone for all your questions and contributions.