# 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 andrew@str8ts.com.
**Post a Comment or Question here...**

## Friday 30-Jan-2009

## ... by: Ygor, Netherands

This is a great site! I am wondering what the score is of the most difficult sukoku that your solve can solve? And do you have this sudoku as an example?

Cheers,

Ygor

THIS ONE

which I score as 2528 but this won't show up on the web site grader as I exclude Nishio/Bowmans, but you are welcome to discover a better solve solution that doesn't involve them - I'd be very interested to see one.

## Wednesday 28-Jan-2009

## ... by: Dena, US

Load Sudoku: CLICK TO LOADI love your solver but the explanations sometimes omit information. Maybe if you are really good at Sudoku it is obvious but I'm still a novice.

Thanks for your help!

/Hidden_Unique_Rectangles

and there is now a link to it from the solver.

Hope that helps!

## Thursday 22-Jan-2009

## ... by: JimF, Australia

5..8 8..5

8..5 5..8

But if you can swap the 5/8 values after the puzzle is finished and still have a valid solution, how could we ever have deduced the values of 5, 8 and 5 for C4, C7, and B7 respectively in the first place? Any 5's or 8's in the bottom two thirds of the puzzle can restrict which columns can contain a 5 or 8 in the top third of the puzzle, but not which rows can contain them. i.e. they can't have any impact upon whether we have 5 in B7 and 8 in C7 as opposed to the other way around. The values of C4, C7 and B7 are dependent upon each other; we need to know one of them to be able to determine the other two. But if we know none of them, then C4/C7/B7 can have values of 5/8/5 or 8/5/8.

So my problem is that I don't see how this particular example could ever occur in real life.

If we undo those three cells, the possibilities for those cells are:

B4: 589 B7: 58

C5: 58 C7: 58

and we can then use the Unique Rectangles algorithm to determine that B4 is 9, which quickly allows lots of other cells to be solved.

.8.7...5..9.523.6..........3.6...8.7.58...

62.9.4...1.5..........4.958.7..6...7.4.

There are infact many ways to crack the numbers in those four cells, I just turned off strategies that did so at that point and tried again. I don't have a facility to cycle through all URs for example, the solver only returns the first it finds and then insists on moving on. But yes you can use UR to solve it. However, its very common for strategies to overlap.

I feel ARs stand out more than URs and since it’s a very interesting strategy it's worth documenting. Also note I've not actually added Avoidable Rectangles to the program yet. What I need to do it implement it fully and run through a very large stock to see if it’s a necessary strategy, that is, if it is used when all other URs have been tested for.

Will add to my job pile :)

## Friday 9-Jan-2009

## ... by: Seong-OK, Korea

Load Sudoku: CLICK TO LOADThanks for an excellent slover. I got a lot of help from your tool..

While I'm trying to solve the puzzle above, your solver stoped after displaying results of pointing pair step..

Would you check if there is any problem in your tool ???

Thanks and Happy new year...

## Sunday 4-Jan-2009

## ... by: Stephen Hotchkis, Scotland

Load Sudoku: CLICK TO LOADAlso not sure of the significance of the grren and yellow squares

http://www.sudokuwiki.org/Sword_Fish_Strategy

## Saturday 3-Jan-2009

## ... by: Wayne, Canada

Thank you Wayne!