Baffled by VERY HARD puzzle

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Baffled by VERY HARD puzzle

Postby Michael » Thu Apr 14, 2005 11:10 am

I am new to Sudoku puzzles and am baffled by a very hard puzzle generated by the Sudoku program. The literature states that all generated puzzles are solvabe using logic only. Trial & error not necessary.

This is what I've got so far. I turned on the Flag Wrong Answers, so am certain there are no mistakes.


* 5 4 * 9 8 * * *
2 * * 4 5 7 * 9 *
* * 9 * 6 1 4 * 5
* 8 * 1 4 3 * * 9
* * * 9 7 6 * * *
9 * * 5 8 2 * 1 *
6 2 3 7 1 5 9 * *
* 9 * 8 3 4 * * 6
* * * 6 2 9 1 5 3

I pencil marked all empty cells, but cannot find any thing that helps to eliminate all but 0one pencil mark.

Any help is appreciated.

Thank You.
Michael
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Re: Baffled by VERY HARD puzzle

Postby shakers » Thu Apr 14, 2005 1:56 pm

Michael wrote:I am new to Sudoku puzzles and am baffled by a very hard puzzle generated by the Sudoku program. The literature states that all generated puzzles are solvabe using logic only. Trial & error not necessary.


Not the reply I'm sure you were hoping for, but thought you may like to know that you're not alone in your bafflement..!
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Postby Guest » Thu Apr 14, 2005 2:02 pm

X-wing ahoy! Digit 3, rows 2 & 6
Guest
 

Postby shakers » Thu Apr 14, 2005 2:07 pm

IJ wrote:X-wing ahoy! Digit 3, rows 2 & 6


About to show my ignorance... but I thought X-Wings worked with pairs of digits?

Why is the X with R2 and R6, rather than R2 and R5 if only one digit is needed?
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Postby Michael » Thu Apr 14, 2005 2:22 pm

To IJ:
Thank You, Thank You, Thank You.
I had read about x-wings but did not know how it worked. I do now.
Hopefully I can finish the puzzle.
Thanks again.
Michael

To Shakers:
I believe x-wing refers to the same digit that can only be in the same row/column in 2 different rows/columns. IJ's clue eliminates the digit 3 in columns 2 and 7, making r3c2 a 7.
Michael
 
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Postby shakers » Thu Apr 14, 2005 2:36 pm

Michael wrote:I believe x-wing refers to the same digit that can only be in the same row/column in 2 different rows/columns. IJ's clue eliminates the digit 3 in columns 2 and 7, making r3c2 a 7.


OK... but I still cannot see why it had to be R2 and R6, rather than R2 and R5.
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Postby Michael » Thu Apr 14, 2005 2:53 pm

R2 and R6 can have a 3 in columns 2 and 7 only.

R5 can have a 3 in columns 1, 2, 7 and 8.

By using R2 and R6 you can determine that the 3 for column 2 is either in R2 or R6 and cannot be in any other row.

BTW I use the Sudoku program. I found it is much easier to use pencilmarks than paper and pencil.

Good Luck.
Michael
 
Posts: 9
Joined: 14 April 2005

Postby shakers » Thu Apr 14, 2005 3:04 pm

Michael wrote:R2 and R6 can have a 3 in columns 2 and 7 only.

R5 can have a 3 in columns 1, 2, 7 and 8.

By using R2 and R6 you can determine that the 3 for column 2 is either in R2 or R6 and cannot be in any other row.

BTW I use the Sudoku program. I found it is much easier to use pencilmarks than paper and pencil.


Thanks - suddenly that makes more sense... I think I got confused in the original discussions of X-Wings a couple of weeks back.
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Postby jayal » Tue Apr 19, 2005 5:03 am

try this
154398627
268457391
379261485
782143569
415976832
936582714
623715948
591834276
847629153
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Postby Guest » Tue Apr 19, 2005 7:00 am

Jayal,

Thanks. Once I understood the x-wing concept, things started falling into place.
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Baffled by VERY HARD puzzle

Postby tlicious12 » Thu Apr 21, 2005 2:27 am

I hope this helps.. i don't know if you solved it yet.

* 5 4 * 9 8 * * *
2 * * 4 5 7 * 9 *
* * 9 * 6 1 4 * 5
* 8 * 1 4 3 * * 9
* * * 9 7 6 * * *
9 * * 5 8 2 * 1 *
6 2 3 7 1 5 9 * *
* 9 * 8 3 4 * * 6
* * * 6 2 9 1 5 3

Answer:

1 5 4 3 8 9 6 2 7
2 6 8 4 5 7 3 9 1
3 7 9 2 6 1 4 8 5
7 8 2 1 4 3 5 8 9
4 1 5 9 7 6 8 3 2
9 3 6 5 8 2 7 1 4
6 2 3 7 1 5 9 4 8
5 9 1 8 3 4 2 7 6
8 4 7 6 2 9 1 5 3


Tasha
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Re: Baffled by VERY HARD puzzle

Postby Tony Williams » Fri Apr 22, 2005 6:05 am

Michael wrote:I am new to Sudoku puzzles and am baffled by a very hard puzzle generated by the Sudoku program. The literature states that all generated puzzles are solvabe using logic only. Trial & error not necessary.

This is what I've got so far. I turned on the Flag Wrong Answers, so am certain there are no mistakes.


* 5 4 * 9 8 * * *
2 * * 4 5 7 * 9 *
* * 9 * 6 1 4 * 5
* 8 * 1 4 3 * * 9
* * * 9 7 6 * * *
9 * * 5 8 2 * 1 *
6 2 3 7 1 5 9 * *
* 9 * 8 3 4 * * 6
* * * 6 2 9 1 5 3

I pencil marked all empty cells, but cannot find any thing that helps to eliminate all but 0one pencil mark.

Any help is appreciated.

Thank You.
Michael


This should explain the next steps - the X-Wing is the key needed to free off this puzzle for a solution ...... once past iteration 4 it is all downhill to the solution [not included]:D

Code: Select all
 - - - - - - - - - - - - - - -
Iteration Number  1
 - - - - - - - - - - - - - - -
Testing for Unique Placements
Test all Digits for unique to Row/Col/Sq
Testing only Row/col in Square
Digit 6 occurs only in Row 2 - Square 1
Digit  6 not allowed Cell( 2, 7)
Digit 7 occurs only in Row 8 - Square 9
Digit  7 not allowed Cell( 8, 1)
Digit  7 not allowed Cell( 8, 3)
 - - - - - - - - - - - - - - -
Iteration Number  2
 - - - - - - - - - - - - - - -
Testing for Unique Placements
Test all Digits for unique to Row/Col/Sq
Testing only Row/col in Square
Testing for Pairs/Triplets [Rows]
Testing for Pairs/Triplets [Columns]
Testing for x,y Pairs of Digits [Rows]
Testing for x,y Pairs of Digits [Columns]
Testing N-Cell Candidates [Rows]
Testing N-Cell Candidates [Cols]
Testing N-Cell Candidates [SQs]
Testing for X_Wings [Rows]
X_Wing Rule - Digit   3 at Rows  2 & 6 are a Pairs into Columns =  27
Digit  3 not allowed Cell( 1, 7)
Digit  3 not allowed Cell( 3, 2)
Digit  3 not allowed Cell( 5, 2)
Digit  3 not allowed Cell( 5, 7)
Testing for X_Wings [Columns]
 - - - - - - - - - - - - - - -
Iteration Number  3
 - - - - - - - - - - - - - - -
Testing for Unique Placements
 46 - Digit  7 only candidate for Cell( 3, 2)
 47 - Digit  4 only candidate for Cell( 9, 2)
 48 - Digit  1 only candidate for Cell( 5, 2)
Test all Digits for unique to Row/Col/Sq
 49 - Cell( 5, 1) = 4
 50 - Digit  4 Only position in Row( 6) is Cell( 6, 9)
 51 - Digit  7 Only position in Column( 9) is Cell( 1, 9)

etc - downhill from here
====================
  Puzzle Solved
 ====================

:)
Tony Williams
 
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