# 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...**
## Wednesday 3-Nov-2021

## ... by: Allan Patrick, United States

## Wednesday 27-Oct-2021

## ... by: Carl, Florida

Load Sudoku: CLICK TO LOADThe correct solution is based on D3=6 chosen to eliminate the possibility of an alternate solution.

There is no "correct" solution since there isn't a single solution. BUG is among a group of strategies that specifically rely on there being a single solution. But all logical strategies will be deceived ultimately.

## Monday 25-Oct-2021

## ... by: Larry Zwahlen, Canton, GA, USA

Sorry for the late reply

Try the solver to see how the solutions are derived

(I notice the player and solver have different colours so I've synchronized them)

## Thursday 21-Oct-2021

## ... by: jamsaw, USA

The problem is, other sites have different names for units...some call a 3x3 unit "box", some call it "square", some call it "region". So, when reading the instructions or analysis, it become confusing if you have ever been exposed to other Sudoku sites. Is there any chance you could describe your terminology at the beginning of the explanations? I wish there were a common terminology where everyone had the same unit names in mind.

Also, where are you, where J follows H in the alphabet?

Also very early on people decided that "I" was too close to "1" for a row name and therefore J follows H for row names. This was generally agreed to be a good idea as coordinates need to be very clear. A large fraction continue to use the cumbersome rXcY format

I've also added a Glossary

## Tuesday 19-Oct-2021

## ... by: Obi, UK

Load Sudoku: CLICK TO LOADI believe I've found a bit of an inconsistency with the way the solver applies (at least) hidden singles in the solve path. In the sudoku provided, step 10 lists the following hidden singles:

4 found once at r1c2 in row, 4 candidates removed

6 found once at r1c1 in row, 1 candidate removed

8 found once at r9c5 in column/box, 1 candidate removed

The problem is with r1c1: the 6 is only found once in the row because it has been eliminated from r1c2 in the same round. This elimination is therefore not deducible from the state of the board at step 10.

Stepping through the steps manually on the solver separates these steps.

Maybe there is a reason the solve path wants to group these steps, but it seems bizarre to me.

Thanks again

This didn't seem important when I wrote it since all the other strategies were the interesting ones and this was a process for clearing off candidates from singles to get to the meat. But I should address it in the next update.

If you are comparing a puzzle with a score 68 to another with a score of 72 I wouldn't say one was more difficult than the other since there are a host of subjective decisions (exact points for any strategy eg) but 68 compared to 300 or 3000 is significant. Its for the bulk division of all puzzles into grades but the dividing line is arbitrary. It's like a bell chart of human heights. If you want to divide people into short and tall the division will separate people with millimetre height differences around the average

## Saturday 21-Aug-2021

## ... by: Frank Merritt, Illinois, USA

I have never understood the labeling of shapes in Jigsaw configurations. Judging from the labels for Andrew Stuart 7 and for Cabbage, I believe they are labeled by whim rather than by any systematic procedure. Is that correct? If not, is the rule explained anywhere in your pages?

P.S. Thanks very much for such an incredibly useful reference!

There is a complete list of the jigsaw shapes here

Now I believe I have tried to assign the numbers in a top-left to bottom-right order but not every shape has that determination I can see

I might go back and renumber, next update

## Monday 16-Aug-2021

## ... by: Theo, Switzerland

One small question: I have edited off some possibles in any Sudoku. With the "auto clear" button on, when I enter a solution, the action taken by the solver is not to logically clear out just the values that have to be cleared in that box, row and column because of this new number, but it resets ALL possibilities back. Meaning, my edits are discarded, the possibilities I edited out earlier are set back again. Could there be an option to make a real clearing, not a reset to all possibilities?

This sounds so easy, am I missing something?

Best regards, Theo

## Tuesday 10-Aug-2021

## ... by: brent hudson, United Kingdom

Firstly, what a brilliant programme! I have used it a lot over the last 2 years as I've tried to improve my own solving skills. It has helped me improve a lot.

However, on this board I have been able to solve a puzzle that the solver cannot, and I would expect it to be able to. I am wondering why it cannot.

Here's the board:

There is a Killer Sudoku board I would like you to look at

Click on this link:

https://www.sudokuwiki.org/killersudoku.htm?bd=121112211121133441112213122132112111332312322111311321221213311133221121114411121,300622000012002100000000001600040000000025003200191400000600000013000000000000130000151200210000000000000022130000210000000000180500000027001000000008000000000000

When it gets stuck, cells G6, H6, J5, and J6 sum to 13 (by summing columns 7, 8, and 9 and looking at the spill over). 13 in 4 cells in the same block has to contain 1. This means that J4 has to be 2 (the solver gets stuck with J4 being only 1 or 2).

If I set J4 to 2, the solver then solves the puzzle.

Why doesn't the solver see that J4 has to be 2?

I ask for two reasons:

1. The solver seems to solve much harder situations than this one.

2. If you do decide to update the solver again, maybe there's a piece of logic you could insert?

Again - thanks for doing the solver; it's a great tool!

Brent

## Sunday 8-Aug-2021

## ... by: Kelly, Belgium

I have a really difficult (Double) Jigsaw Sudoku I want help solving with. The grid of the jigsaw is not one of your grids. How can i make my own grid and use your solver?

Thank you so much in advance!

Kind regards,

Kelly

## Monday 5-Jul-2021

## ... by: Jurgen, Belgium

I'm trying to enter a puzzle in the small grid on the left but when I type 8 it gets replaced with a 9 ....

I was trying something to get ipad keyboards to map letters to numbers and I can't work out why it's effecting normal keyboard usage (I can't duplicate) so I've reversed the changes

Tell me if it's back to normal.