Solver App for Android
Strategies for Popular Number Puzzles
Page:2024 2023 2022 2021 2020 2019 2018 2017
2015 2014 :1 2 3 4 5 6 7 :2013 2012 2011 2010 2009 2008 2007 2006

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 .

Post a Comment or Question here...
Your Name or 'Handle'

Part of the World you're from

Email Address (optional) so I can reply directly if necessary (it will not be displayed here)

Any Sudoku you want to publish here for easy loading into the solver - 81 characters, use '.' or '0' for unknowns.

public - comment/question will be added to feedback column
private - email comment/question directly to Andrew Stuart, don't display here

Comment, question or feedback:

Enter these letters
Please enter the
letters you see:

Many thanks to all the people who have helped improve the solvers and strategies with their feedback!

Tuesday 5-Aug-2014

... by: pat field, wisconsin

Dear Andrew,

Love your site. But recently I have been having problems when I access it on Chrome (no problems on Internet Explorer, same computer).

Problems: cannot activate Auto Clear

Delay in entering data from left screen to main screen: it takes one more keystroke for the (last) entry to show up. I am also experiencing a one keystroke delay as I type this complaint (which is disconcerting).

I'm a big fan, nevertheless.


Andrew Stuart writes:
That's very strange behaviour. It does sound like a chrome-client side thing. No having any problems on my chrome, nor have I added anything recently that should effect it. Difficult to say. Tried clearing your cache?

Tuesday 5-Aug-2014

... by: TimCinOR, Oregon

Great site!

Especially thanks for the stepper, and the explanations of the strategies. I've got a puzzle that has some strategies for me to learn.


Wednesday 30-Jul-2014

... by: Robert Campbell, USA

I cannot maneuver through your opening screen that has too much information on it for me to know where to start. Please offer some help. I want to learn how to do easy sudoku

Andrew Stuart writes:
Hi Robert
Start here:

I agree, I need to make it easier to find that page from the start

Best of luck solving!

Thursday 17-Jul-2014

... by: Kai Bachmann, Austria

Load Sudoku:

This Sudoku uses three times the XY-Chains strategy (solving steps 11, 12 and 13) with the same cells C3, C4, C5, F4 and F5, changing only the starting/ending point of the chain, and eliminates candidates 4 in cell C7, 1 in cells A5 and B5, and 2 in cell F6.
A nice example to show how a same chain, varying its starting/ending point, can exlude many different candidates.

Andrew Stuart writes:
An excellent example, well found

Monday 7-Jul-2014

... by: Mike, USA

Was looking at X-cycles>Part 2>Nice Loops Rule 2> last paragraph. "We have two strong links joined at J1; therefore, J1 is 1. One way to make sense of this logically is to trace round the alternative. If J1 was not a 1 G3 and J8 would have to be 1s. That would remove the candidate 1 from E3 and oblige E8 to be a 1. But hang on - that forces two 1s in column 8. A contradiction so the 1 must exist in J1."

I think is should be it forces two 2s in row E. I"m not seeing the two 1's in column 8. Please explain it to me if I'm wrong. BTW love what you did here, it so cool.

Andrew Stuart writes:
If J1 != 1 then it makes J8 = 1 (only two 1s in row J)
If J1 != 1 then G3 = 1 -> E3 != 1 -> E8 = 1 (only two 1s in row E)
So we get a 1 in both E8 and J8. Doesn’t matter there is a third 1 in the column (A8), it’s a contradiction that we get two positives in the column. That clinches it

Thursday 3-Jul-2014

... by: Kyle, Antarctic

I would like to report some serious problems about the SudokuX solver.Some of the advanced strategies dismiss strong links within diagonals.The sudoku X puzzle I display here proved to be a extreme one.Jsudoku created the puzzle,who could only use easy strategies like Xcycles,XYX chains and ALS.

Load puzzle

After several pointing and box line reduction,the next two steps Jsudoku taken were grouped Xcycles.The first one is:
+9C9 -9G9H9 +9G7H8 -9B2 +9B5 -9C5 +9C9...
This is a grouped Xcycle rule 1 ,9 in A5,E9 should be removed.It seems the solver failed to recognize groups in diagonal (or just dismiss diagonals)However,the solver jumped directly to NFC to remove 2 inC6.In fact,there is a AIC:
+2C6 -8C6 +8C9 -8A9 +8J1 -4J1 +4G3 -4C3 +2C3 -2C6
2 inC6should be removed in this way,with nice loop rule 3.The only reason I could come up with is that the strong link -8A9 +8J1 was dismissed.
Then,after some extreme strategies,the solver ran out.However,some easy steps can still be taken.For example:
+5H8 -5B8 +5C7 -5C1 +5A1 -5H8
5 in H8 should be removed.This is a very easy Xcycle or simple coloring.Again,the solver failed to recognize.In addition,I could hardly see any strong links in diagonals was used in the solver.I really like your solver and have used for years.The sudoku solver is quite good,but SudokuX solver definitely needs improment.

Andrew Stuart writes:
Guilty as charged! But in my defence I get very few feedbacks on the X version of the solver and you're the first to discover the grouped cells problem on diagonals.

[edit] Finished the update. This example is now found and the puzzle completes, although its a beast.

Good detailed example, most appreciated!

Saturday 21-Jun-2014

... by: Dick, USA

Used to be the candidates were printed on the bottom of each cell. Now they are scattered throughout the cell which makes it hard went entering the correct number. Is there a way to have the candidates printed on the bottom of each cell.

Andrew Stuart writes:
[Print 1] *should* display the candidates in the top of each cell, in a row. [Print 2] puts them centrally in a 3x3 grid. Not sure how you ever saw them in the bottom. Talking about this solver :- ?

However, if you have your browser to be zoomed in/out, especially the text, this will distort the layout. Reset zoom levels?

Tuesday 10-Jun-2014

... by: Geoff, australia

Firstly, thankyou for your wonderful site. Your instructions have allowed me to solve most of the published puzzles, but I want to practice the tough strategies, 7 to 11. How can I find Sudoku puzzles that have these strategies in them, or is there somewhere I can generate them? Thank you again.

Andrew Stuart writes:
Glad you like the site. Check the daily puzzles
and pick the diabolical ones. The archive calendar has at least eight. Also, the puzzle packs
you want the diabolical and extremes

Wednesday 14-May-2014

... by: nono, france

Hi Andrew,
well, the future e-book !
thanks for the new compilation .
for this year ?

Andrew Stuart writes:
Hopefully yes!

Thursday 8-May-2014

... by: Bruce K, Portland, OR

Here's another interesting one. This is one that is defeating me, so I tried feeding t into your solver.

Two problems: First, it seems to cause a failure to solve the four-color problem while entering it. Then the solver runs out of strategies,
Not sure it's a bad puzzle or a solver limitation.

Andrew Stuart writes:
Well it had to happen, a pattern that my crude color mapping algorithm cant cope with. I've added a 6th color and it loads correctly now.

Try this link

My Killer solver is lagging behind the normal Sudoku solver. There is a significant subset (~10%) of killers which is draws a blank on. Still a lot of new ideas that have to be dug up
Page:2024 2023 2022 2021 2020 2019 2018 2017
2015 2014 :1 2 3 4 5 6 7 :2013 2012 2011 2010 2009 2008 2007 2006
Thank-you everyone for all your questions and contributions.