PLEASE HELP ME solve a Very Hard puzzle

Advanced methods and approaches for solving Sudoku puzzles

PLEASE HELP ME solve a Very Hard puzzle

Postby Art Hedgehog » Sun Jun 12, 2005 6:58 pm

I have no idea how to use forums or how to attach my puzzle to this memo.

I have managed to do about 100 Very Hard puzzles produced by the Su Doku program but 2 have got me stumped.

I have tried to read a bit about solving techniques in this forum thing and have tried to apply the Swordfish technique to the puzzle I am stuck on but without success.

Well here is as far as I have got with the puzzle. If anyone can tell me how to attach a ".sud" file or another way or presenting this better then please let me know.

Code: Select all
 2 3 8 | 5 . . | 4 . 9
 4 . . | . . . | 3 7 8
 . 9 7 | 3 4 8 | . 2 5
-------+-------+------
 3 4 2 | 6 8 . | . 9 1
 . 8 . | . . . | . 3 .
 7 . . | . 3 1 | 8 4 .
-------+-------+------
 9 7 3 | . 5 . | . . 4
 5 2 6 | . . . | . . 3
 8 1 4 | . . 3 | 9 5 .

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Postby Animator » Sun Jun 12, 2005 7:23 pm

You claim to have solved 100 very hard puzzles so all I'm going to say is look at box 8.

(Also note that the Swordfish technique is not required to solve very hard puzzles... )
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Hello "Animator" - I am STILL stuck

Postby Art Hedgehog » Wed Jun 15, 2005 6:08 pm

I still don't know what I am doing. Why do I need to enter a subject when it should just be a new entry under my original Subject?

I only checked to see if anyone had posted a reply this evening as I really didn't expect any. It looks like you replied within half an hour!

Honestly, I have solved about 100 Very Hard puzzles from the Su Doku program but I am STILL stuck on this one.

The processes I use are as follows:

Enter all possibles (referred to as candidates I think). This is the first step and shows up any immediately obvious definites.

Directional Deleting. I think this might be referred to as eliminating candidates. For example, if a 4 in grid X has to be in row Y then it cannot be a candidate elsewhere in row Y.

Pairs. If a couple of numbers are only candidates in 2 cells within a grid, row or column (GRC) then those cells can ONLY contain those numbers.

Triples. Like pairs but 3 numbers and 3 cells.

Unique doubles. The official term is X-something and is the 2x2 version of the swordfish technique (I think). This is where a number can only be in 2 positions in 2 rows/columns, ... You know what I mean.

I have looked for all these techniques in this puzzle, including grid 8 (which I presume is the middle-bottom one).

Out of interest, a work colleague told me of an on-line solver today at http://www.sudokusolver.co.uk/step.html. This can't solve the puzzle without guessing.

Anyway, please just tell me what I can do in grid 8.

I apologise in advance if it is something that I do know (i.e. one of the techniques above) but I do get a sort of "Su Doku blindness" every so often. In the early days of the puzzles appearing in The Times, Wayne Gould offered a personal service where if you emailed him the puzzle in ".sud" format, he would give you the next move. I used Wayne a few times and every time the solution was something that I knew. I felt stupid but it did give me the confidence to solve all the puzzles since. That was until a couple of months ago when I got REALLY stuck for the first time and I gave up doing the puzzles. It was my Dad who got me going again but now I am stuck again and am really starting to lose faith.

Off this topic a bit, have you tried the Samurai Su Doku puzzles in the Times on Saturdays? I have only seen the ones from 4 and 11 June. The 4 June one wasn't too difficult but it took me about 70 minutes against the guide time of 55 minutes. The 11 June one however took me virtually 3 hours (target time of 85 minutes). If you have seen these, how long did they take you and are you going to enter the national championships?

Well that was quite a long entry. Hope I haven't bored you (if you have even seen it).

Regards

Gareth
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Postby Animator » Wed Jun 15, 2005 6:43 pm

(You can leave the Subject empty if you want... it's just a title that is added above your post...)

First take a really good look at box 8 (hint: 3 cells).

When you saw what I see, then look where the number 7 can go in box 9...

And it sure is solvable without guessing. So I suggest you use another solver :).
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Postby Art Hedgehog » Wed Jun 15, 2005 6:53 pm

Sorry, I still don't see anything.

7 is a candidate in 5 of the cells in grid 8. there is no directional deleting available.

I honestly can't see a triple.

Please, just tell me.
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Postby Animator » Wed Jun 15, 2005 8:22 pm

2, 6, 7?
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Postby Sudoku Master » Thu Jun 16, 2005 3:02 am

:DIt is not hard at all. If you have tried all techniques but it yield no solution, you needs a smart fifty fifty assumption. Let's look at the first box in the third row from the top to find all possibility. You have two choice: 1 or 6. Pray and pick one number and start from there. I pick number 1 and I can play on and on until I finish the game. When I pick the 6, I have error on the first row at the third box on the right (I need number 4 but it contradicts with number 4 on the second box). It tells me that number 6 is a wrong choice.

Good Luck

Suzuki Honda Toyota Mazda Kawasaki:)
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Postby angusj » Thu Jun 16, 2005 3:14 am

Sudoku Master wrote::DIt is not hard at all. If you have tried all techniques but it yield no solution, you needs a smart fifty fifty assumption.


To me, Sudoku is a logical puzzle, and as such guessing (trial and error) would remove the pleasure of solving them.

I'd rather stick with a puzzle which remains unsolvable based on current logic and work towards uncovering new logical rules.

If you just want a solution, and not the mental challenge, then there are dozens of websites and downloadable solvers which can solve the 'unsolvable'.
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Re: Hello "Animator" - I am STILL stuck

Postby angusj » Thu Jun 16, 2005 3:27 am

Art Hedgehog wrote:Anyway, please just tell me what I can do in grid 8.


There is what I call a Naked Triple there:
http://www.angusj.com/sudoku/hints.php#naked_triples
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Postby Sudoku Master » Thu Jun 16, 2005 3:53 am

:D

Hi! I see all your "naked techniques" are another way of logical guessing. You makes a simple work to become complex.


:D
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Postby angusj » Thu Jun 16, 2005 4:18 am

Sudoku Master wrote::D
Hi! I see all your "naked techniques" are another way of logical guessing. You makes a simple work to become complex.


I'm not quite sure what you mean by a logical guess. Applying logic is not guessing.

As to your comment about making something simple complex - are you referring to my Solving Hints webpage? If so, yes, I agree that much of it is very badly written - so I apologise for that. I only put it together yesterday so it's very much a draft, or work in progress and far from finished. Some of the labels I've used to express logical steps I'm not happy with either so they're likely to change. If you want to make suggestions as to how I could express a step more clearly that'd be great.
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Postby greengrass » Thu Jun 16, 2005 7:42 am

are you referring to my Solving Hints webpage? If so, yes, I agree that much of it is very badly written - so I apologise for that. I only put it together yesterday so it's very much a draft, or work in progress and far from finished. Some of the labels I've used to express logical steps I'm not happy with either so they're likely to change. If you want to make suggestions as to how I could express a step more clearly that'd be great.


I think there is a "bug" in your "Required by Another" example

"On the right, the lower 3x3 box only has possible 3's in its middle column. Since, one of those cells must be a 3, no other cells in that column can be a 3. Therefore 3's can be excluded from the middle column in the upper 3x3 box. "

But it would appear a 3 can appear in column 1, see the bottom left cell which possible contains 4 and 3!
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Postby angusj » Thu Jun 16, 2005 9:22 am

greengrass wrote:I think there is a "bug" in your "Required by Another" example


Thanks.
I've spent a bit more time improving my hints webpage (but still some way to go), and I've also fixed up that bug you mentioned.
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Postby BadCujo » Thu Jun 16, 2005 11:59 am

In your example of "Naked Triples", would it not be easier to eliminate the 2&5 based on the hidden pair 8&6?
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Postby angusj » Thu Jun 16, 2005 12:38 pm

BadCujo wrote:In your example of "Naked Triples", would it not be easier to eliminate the 2&5 based on the hidden pair 8&6?


Yes you're right. I simply pushed this logical step to the top of the hint stack in my Simple Sudoku solver to speed up the process of finding an example. Looks like you've caught me out.:)

Looks like I'll have to fix the Naked Quad example too.

To avoid dragging this thread totally off topic could I suggest that any further suggestions/corrections for my Hints page go here:
http://forum.enjoysudoku.com/viewtopic.php?t=509
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