# 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...**
## Saturday 23-Apr-2016

## ... by: Sean, Omaha

## Thursday 21-Apr-2016

## ... by: Eyad Khalil, Palestine

Can the Daily Puzzles listed on your site be automatically imported into the Solver - without having to enter the 81 digits one at a time?

Thanks,

## Thursday 21-Apr-2016

## ... by: Bert, Netherlands

last few days: unable to update kakuro puzzles:

Could't reach the Internet to pick up the puzzles.

No problems with the other puzzles.

Appreciate the alert!

## Tuesday 19-Apr-2016

## ... by: Chris Green, Australia

I just solved Unsolvable #196, using a simple program I wrote (to save laborious work) plus a trial and error approach. I guess such an approach is not considered very valid since Andrew seems to be looking for more logic-based approaches.

Anyway, it took me 22 tries but when I eliminate the erroneous tries, it can be solved in 6 tries. (Of course, that's a case of 20/20 vision in hindsight!) I chose to start with Box 9 because it has the least number of possible candidates at the beginning.

The sequence I chose was: J8 =3, J2 =1, E1 = 1, B1=5, J4 =6 and finally, J3 = 5 for completion.

A New Metric for Difficult Sudoku Puzzles

which follows on from

Arto Inkala Sudoku

## Thursday 14-Apr-2016

## ... by: UL, Hong Kong

Load Sudoku: CLICK TO LOAD-1[G2]+4{G2?E2}

I don't understand this strong link in the puzzle, could you please explain it?

## Saturday 26-Mar-2016

## ... by: Uhm, Netherlands

Your solver does not find easy boxline reductions or pointing pairs, instead it finds x-cycles which does slowly the same reduction.

As you documented in:

http://www.sudokuwiki.org/Windoku_Strategy

A windoku is just a double sudoku, 1 constraint extra for each cell.

The first x-cycle it find is at 2 in column 5, which is just an boxline reduction from that cell. So you can exclude more which an easier strategie, those x-cycles are apparently hard for your solver.

Cheers

Edit 27 March: I have added in proper Pointing Pairs and Line/Box Reduction for 'windows'. I am recalibrating the grades as a result and will provide new examples in the solver example list.

## Friday 25-Mar-2016

## ... by: David Munson, Los Angeles, California, USA

Load Sudoku: CLICK TO LOADI have been noticing problems with the Sudoku solver. I'm working from Los Angeles, California, U.S.A. I cleared all my browsing data in Google Chrome, this includes "cached images and files". I have noticed that the Solver is no longer finding X-Cycles and it seems to also not be finding AICs.

Here is an example position; it is from your Jan 2016 Diabolical Puzzle Pack puzzle #14. From this position, after the Sudoku Solver gets through the basic 6 rules, the Solver finds an X-Wing that cancels two 9's.

Next after going thru the basic 6 rules, it finds an XYZ-Wing. But if XYZ-Wing is de-selected, then the solver should find an X-Cycle for 8's which cancels one 8. But it does not. Instead it finds an XY-Chain. Here is the X-Cycle for 8's: +8[B4]-8[B7]+8[C9]-8[H9]+8[H4]-8[B4]. This is Nice Loops Rule 3.

Also, after canceling the 8 on B4, then if we de-select all the rules from XYZ-Wing to Finned Sword-Fish, now the Solver should find an AIC. But the Solver proceeds on to Digit Forcing Chains. There are probably many AICs in this position, here's one of them: +3[B4]-3[B6]+8[B6]-8[B7]+8[C9]-8[H9]+6[H9]-6[H4]+8[H4]-8[G4]+3[G4]-3[B4]. Another Nice Loop Rule 3.

A month or so ago things were working fine. This happens for other puzzles too. I tried the above position in Windows Explorer as well as Google Chrome, same result. I still have Windows Vista Ultimate; don't know if that makes a difference.

Thanks for your time,

from Dave Munson

## Thursday 25-Feb-2016

## ... by: JB, France

Load Sudoku: CLICK TO LOADI tried to solve a sudoku with your solver, but it failed when applying the "Alternating inference chains" technique. The solver excluded digit 3 from J6, which is actually the correct value. As a result, the solver gets stuck later and finds no solution. Could there be a bug concerning this technique? I don't understand it myself, so I can't tell what the problem is...

But I can assure that this sudoku has a solution, as I solved it manually and verified it!

JB

Thanks for sharing

Edit: 29th Feb 2016: Fixed. Put in a check in the correct place and now this false positive does not occur.

## Wednesday 17-Feb-2016

## ... by: Wolfgang Lentner, Bavaria

I checked a SUDOKU with your solver and saw something strange?!

SUDOKU: 000798354030514620000632108000006503020351400543987216370069845000800700080070900 has 83 solutions

using on this SUDOKU your strategie 26: "Altern. Inference Chains", we get ...

SUDOKU: 000798354030514620000632108000006503020351400543987216370069845000840700080070900, which has 58 solutions?!

How can the solutions get less, after a correct conclusion?

Doesn't this mean, that the "new" 4 in H5 isn't a correct conclusion?!

greatings from bavaria

Wolfgang

Did you miss a clue or mis-type a clue?

## Sunday 14-Feb-2016

## ... by: dimanche, france

Many solvers, congratulations.

Solutions clearly explained...

What about an application which should built a sudoku at the level of your choice ?

For instance, suppose you build a scale with 30 different levels.

The user could choice level1+level5+level25, click on a button and a moment later the computer shows the wanted grid...

If this idea has some interest for you, mail me...

## Friday 12-Feb-2016

## ... by: S K JAIN, INDIA

sites.google.com/site/skjgeek

You say "Adrianne's Thread". Do you mean "Ariadne's Thread"?

I remember that strategy when Michael Mepham first published his Sudokus in 2005. It was the "all logic fails me" strategy. Since then the community has expanded the logic space to we need to resort to it less, but I class it as a "trial and error" strategy and therefore outside pattern based logic.