The New Sudoku Players' Forum

[JFistere]

This is "Challenging" puzzle #171 in The Big Book of SoDuKo #1 by Mark Huckvale, Newmarket Press. I have gotten this far:

. 2 4|9 . 3|5 . .
. 7 .|4 1 5|2 . .
3 1 5|7 . 2|. . 9
-----+-----+-----
7 8 .|6 4 .|3 . 5
. 5 .|3 7 .|. . 8
. 4 3|5 2 8|. 6 .
-----+-----+-----
4 9 7|8 3 6|1 5 2
2 6 8|1 5 7|. . .
5 3 1|2 9 4|. . .

I resorted to a program called SoDuKo solver and it tells me that the next number is a 4 that goes in Row 8, Column 9 (under the 2). For the life of me, I cannot figure out why. If that is not the correct number, what would you suggest?

Thanks,
John Fistere

[emm]

Check column 9. Is there any other cell the 4 could go into? If not then it must go there. It's harder to see because it's not the only number that could there, but if it's the only place for that number then it must be the one. It's called a hidden single.

[JFistere]

Thank you, and so fast! and what should have been so easy! <hitting side of head with hand>

Cheers,
John

[Cristian2006]

Can you post the original puzzle?

[Cec]

".. I have gotten this far:.."

Hi John,
To complement em's above help it is better to post the original puzzle and also the stage (pencilmarks or candidates) you reached - this enables us to detect whether you have made a mistake whilst commencing to solve the initial grid. Other recommended procedures for posting puzzles are outlined in this Thread.

Also, submitting your puzzle encased between the "code" tags as described in the above Thread. will then look neater like this:

Code: Select all

. 2 4|9 . 3|5 . .
. 7 .|4 1 5|2 . .
3 1 5|7 . 2|. . 9
-----+-----+-----
7 8 .|6 4 .|3 . 5
. 5 .|3 7 .|. . 8
. 4 3|5 2 8|. 6 .
-----+-----+-----
4 9 7|8 3 6|1 5 2
2 6 8|1 5 7|. . .
5 3 1|2 9 4|. . .


Clicking on the "quote" button of the post you are now reading best explains where these code tags are inserted.

Cec

[Cristian2006]

".. I have gotten this far:.."

Hi John,
To complement em's above help it is better to post the original puzzle and also the stage (pencilmarks or candidates) you reached - this enables us to detect whether you have made a mistake whilst commencing to solve the initial grid. Other recommended procedures for posting puzzles are outlined in this Thread.

Also, submitting your puzzle encased between the "code" tags as described in the above Thread. will then look neater like this:

Code: Select all

. 2 4|9 . 3|5 . .
. 7 .|4 1 5|2 . .
3 1 5|7 . 2|. . 9
-----+-----+-----
7 8 .|6 4 .|3 . 5
. 5 .|3 7 .|. . 8
. 4 3|5 2 8|. 6 .
-----+-----+-----
4 9 7|8 3 6|1 5 2
2 6 8|1 5 7|. . .
5 3 1|2 9 4|. . .


Clicking on the "quote" button of the post you are now reading best explains where these code tags are inserted.

Cec

Well, I think that puzzle is unique so it doesn't actually matter what has happened before. If it's unique when looking at that situation it doesn't matter. The problem just exists...

That was very easy thou.

[Cec]

"..Well, I think that puzzle is unique so it doesn't actually matter what has happened before. If it's unique when looking at that situation it doesn't matter. The problem just exists..."

Well, I thought my comments were clear but obviously not.
Cec

"..I have gotten this far:.."

I mentioned this only to explain how I concluded John didn't submit the initial puzzle.
Cec

My suggestions to John were mainly for future procedure when requesting help, including presentation of puzzles in general, rather than solving this particular puzzle. Frankly, I'm lost on your comment "the problem just exists" - what problem?

Cec

[MCC]

Well, I think that puzzle is unique so it doesn't actually matter what has happened before. If it's unique when looking at that situation it doesn't matter. The problem just exists...

That was very easy thou.

The puzzle may well have had a unique solution before John started, but if he has made a mistake in reaching the position he posted then there will not be a unique solution from there.

MCC

[JFistere]

In this particular case, I knew the solution was correct so far because I had checked it at the back of the book. I didn't see the point in posting the original puzzle in that situation.

If anybody is still interested in the original puzzle, I will be glad to post it.

Cheers,
John

[Cristian2006]

Well, I think that puzzle is unique so it doesn't actually matter what has happened before. If it's unique when looking at that situation it doesn't matter. The problem just exists...

That was very easy thou.

The puzzle may well have had a unique solution before John started, but if he has made a mistake in reaching the position he posted then there will not be a unique solution from there.

MCC

Well, I just thought you can have an uniqueness test. I do that with all the puzzles because there have been crappy ones around and it made me mad.

[Cec]

The puzzle may well have had a unique solution before John started, but if he has made a mistake in reaching the position he posted then there will not be a unique solution from there.

Yes MCC I understood this and which supports my above suggestion why both the original puzzle and subsequent stage reached should be posted when initially seeking help.

In this particular case, I knew the solution was correct so far because I had checked it at the back of the book. I didn't see the point in posting the original puzzle in that situation.
If anybody is still interested in the original puzzle, I will be glad to post it.

Probably no point in submitting the original puzzle now. However I'm sure the suggested procedures (as already mentioned in this thread) for original puzzles to be posted are based on past experiences, including my own "bloopers" where I - and I suspect others - were also "sure" we had posted a correct puzzle or a partly completed puzzle which later revealed was not the case.

"...Well, I think that puzzle is unique so it doesn't actually matter what has happened before. If it's unique when looking at that situation it doesn't matter. The problem just exists..."

If I'm wrong I will apologize but as this comment seems unrelated to my above post where I suggested the forum's recommended procedures for posting puzzles then I don't understand why my previous quotation was fully repeated but then replied to by introducing an unrelated topic which I didn't mention?. Please understand I am not objecting to your post - but only that it should not be related to my post as was the case here which then confused me as to whether you were disagreeing with me or what.

Cec

[MCC]

Well, I think that puzzle is unique so it doesn't actually matter what has happened before. If it's unique when looking at that situation it doesn't matter. The problem just exists...

That was very easy thou.

The puzzle may well have had a unique solution before John started, but if he has made a mistake in reaching the position he posted then there will not be a unique solution from there.

MCC

Well, I just thought you can have an uniqueness test. I do that with all the puzzles because there have been crappy ones around and it made me mad.

That is one reason why the original grid should have been posted. The original could be imputted into a solver and you'll be informed if the puzzle had an unique solution or if it had many solutions.
Just thinking a puzzle is unique is not enough, it must be shown to be unique or in the case of a pappocom puzzle we know that uniqueness is part of the original construct.

Why? when you wrote, "...it doesn't actually matter what has happened before", did you, 2h25m beforehand, ask:

Can you post the original puzzle?

MCC

[Cristian2006]

Well, I think that puzzle is unique so it doesn't actually matter what has happened before. If it's unique when looking at that situation it doesn't matter. The problem just exists...

That was very easy thou.

The puzzle may well have had a unique solution before John started, but if he has made a mistake in reaching the position he posted then there will not be a unique solution from there.

MCC

Well, I just thought you can have an uniqueness test. I do that with all the puzzles because there have been crappy ones around and it made me mad.

That is one reason why the original grid should have been posted. The original could be imputted into a solver and you'll be informed if the puzzle had an unique solution or if it had many solutions.
Just thinking a puzzle is unique is not enough, it must be shown to be unique or in the case of a pappocom puzzle we know that uniqueness is part of the original construct.

Why? when you wrote, "...it doesn't actually matter what has happened before", did you, 2h25m beforehand, ask:

Can you post the original puzzle?

MCC

Yeah, I know... I did that but I noticed you don't need the original puzzle. But of course I prefer posting original sudokus, it just makes things more clear.

I meant later if that current situation has an unique solution what does it matter what has happened before..? Because if you have had a puzzle with many solutions and if you could have made "a mistake" and the puzzle is still solvable after that...it would still have those many solutions, it can't turn to only one solution, can it? And I also meant that it doesn't matter if you have changed that sudoku to another sudoku with your mistakes, because if it has only one solution it's still a valid sudoku and the problem the poster was asking exists. Of course if you don't make an uniqueness test, you just can't know if the puzzle really has only one solution.

[Cristian2006]

---

[Cec]

".. but I noticed you don't need the original puzzle. But of course I prefer posting original sudokus, it just makes things more clear..."

Not only does it make things more clear, posting the original puzzle is one of the procedures which members are encouraged to do as already mentioned many times in previous posts of this and other threads. Even if I thought "you don't need the original puzzle" my intention in submitting the following quotation, which formed part of my above reply to JFistere, was to highlight this desired procedure to always post original puzzles including any submitted in future posts.

To complement em's above help it is better to post the original puzzle and also the stage (pencilmarks or candidates) you reached

See my above comment.
Cec