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peterberg
Joined: 30 May 2013 Posts: 3

Posted: Thu May 30, 2013 5:51 pm Post subject: Very difficult puzzle 


Hi Guys,
I was just wondering, is this puzzle solvable without guessing?
http://www.livesudoku.com/en/sudoku.php?puzzle=1317893
I spent a whole lot of time there and got stuck.
Would love to at least know it's possible to solve using reason only...
Thanks. 

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Marty R.
Joined: 12 Feb 2006 Posts: 5555 Location: Rochester, NY, USA

Posted: Thu May 30, 2013 7:48 pm Post subject: 


How about posting the grid position at which you're stuck?
And yes, it's possible. 

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JC Van Hay
Joined: 13 Jun 2010 Posts: 428 Location: Charleroi, Belgium

Posted: Thu May 30, 2013 7:59 pm Post subject: 


Single digit "techniques" are only required to solve this puzzle ...
Besides Singles and Locked Candidates, the following is needed : r1c3=1.
There are multiple ways to logically justify this. For example :
Code:  ++++
 5 2 9(1)  9(1) 3 8  6 7 4 
 8 79 3  479(1) 479(1) 6  2 5 9(1) 
 179 4 6  1279 1279 5  89(1) 139 1389 
++++
 349 359 49  589(1) 59(1) 7  589(1) 2 6 
 6 1 8  259 259 3  59 4 7 
 79 579 2  589(1) 6 4  3 19 189 
++++
 139 39 7  6 8 2  4 13 5 
 2 8 5  347 47 1  79 6 39 
 134 6 41  357 57 9  7(1) 8 2 
++++  Either r1c3=1 or r1c4=1, r2c9=1 and r4c5=1, r9c7=1 :=> r9c3#1 :=> r1c3=1. 

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keith
Joined: 19 Sep 2005 Posts: 3284 Location: near Detroit, Michigan, USA

Posted: Thu May 30, 2013 8:11 pm Post subject: 


After basics:
Code:  ++++
 9 1 45  45 8 7  2 6 3 
 7 56 8  3456 3456 2  1 9 45 
 456 3 2  1456 1456 9  457 458 4578 
++++
 358 589 35  4579 459 6  4579 1 2 
 2 4 7  159 159 8  59 3 6 
 56 569 1  4579 2 3  8 45 457 
++++
 458 58 6  2 7 1  3 48 9 
 1 7 9  368 36 4  56 2 58 
 348 2 34  689 69 5  46 7 1 
++++

Nice puzzle! I had a Wwing and a bunch of XYwings.
Keith 

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JC Van Hay
Joined: 13 Jun 2010 Posts: 428 Location: Charleroi, Belgium

Posted: Thu May 30, 2013 9:08 pm Post subject: 


The same with Keith's grid but on the digit 4 (r1c3=4) ! 

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Marty R.
Joined: 12 Feb 2006 Posts: 5555 Location: Rochester, NY, USA

Posted: Thu May 30, 2013 9:35 pm Post subject: 


What is going on here? Keith's and JC's grids are different and when I click the link I get a puzzle that doesn't match either of theirs. And clicking the link repeated times gets me a different puzzle each time. 

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JC Van Hay
Joined: 13 Jun 2010 Posts: 428 Location: Charleroi, Belgium

Posted: Thu May 30, 2013 9:42 pm Post subject: 


Marty R. wrote:  What is going on here? Keith's and JC's grids are different and when I click the link I get a puzzle that doesn't match either of theirs. And clicking the link repeated times gets me a different puzzle each time. 
Idem The puzzles are identical up to a permutation of the digits 1 to 9 

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Marty R.
Joined: 12 Feb 2006 Posts: 5555 Location: Rochester, NY, USA

Posted: Thu May 30, 2013 10:02 pm Post subject: 


JC Van Hay wrote:  Marty R. wrote:  What is going on here? Keith's and JC's grids are different and when I click the link I get a puzzle that doesn't match either of theirs. And clicking the link repeated times gets me a different puzzle each time. 
Idem The puzzles are identical up to a permutation of the digits 1 to 9 
Talk to me like I'm eight years old; I don't understand. 

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JC Van Hay
Joined: 13 Jun 2010 Posts: 428 Location: Charleroi, Belgium

Posted: Thu May 30, 2013 10:24 pm Post subject: 


Marty R. wrote:  JC Van Hay wrote:  Marty R. wrote:  What is going on here? Keith's and JC's grids are different and when I click the link I get a puzzle that doesn't match either of theirs. And clicking the link repeated times gets me a different puzzle each time. 
Idem The puzzles are identical up to a permutation of the digits 1 to 9 
Talk to me like I'm eight years old; I don't understand. 
Marty, you get Keith's grid by replacing 123456789 by 418392675 respectively in the grid I posted. To get an idea of the number of equivalent grids, the number of permutations of the digit 1 to 9 is equal to 9.8.7.6.5.4.3.2.1=362880 (9 possibilities for a first digit times 8 possibilities for a second digit times 7 possibilities for a third digit ...) !
JC 

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Marty R.
Joined: 12 Feb 2006 Posts: 5555 Location: Rochester, NY, USA

Posted: Thu May 30, 2013 11:53 pm Post subject: 


I guess I'm hopeless. About 100 years ago I studied permutations and combinations, but I can't get through my thick skull what's going on here. It sounds like Peter is stuck on a particular puzzle and I don't have a clue as to what's going on.
No need to respond; I'm ready to move on. 

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keith
Joined: 19 Sep 2005 Posts: 3284 Location: near Detroit, Michigan, USA

Posted: Fri May 31, 2013 4:55 am Post subject: 


Marty,
Go to the link:
http://www.livesudoku.com/en/sudoku.php?puzzle=1317893
You will see a puzzle.
Now, press F5 to refresh the page. You will see what I think is the same puzzle, except some of the digits are transposed. 4 may become 2 and so on. Press F5 over and over, you get the idea.
Curious.
Keith 

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peterberg
Joined: 30 May 2013 Posts: 3

Posted: Fri May 31, 2013 7:42 am Post subject: 


I see I started a whole new discussion.
Yes the same puzzle has different arrangement every time it loads.
It is I believe because of the scoring system. They measure times and have a high score system so it helps avoid cheating
Anyway thanks for the help, I'm rather new to the whole terminology but I'm starting to learn now, is was solving the easier puzzles till now and they didn't require special skills.
The thing I enjoy the most is the multiplayer option on this website but I'm not as fast as the good players they have in there so I usually lose but still it makes the game a lot more interesting. 

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Marty R.
Joined: 12 Feb 2006 Posts: 5555 Location: Rochester, NY, USA

Posted: Fri May 31, 2013 4:57 pm Post subject: 


Quote:  Now, press F5 to refresh the page. You will see what I think is the same puzzle, except some of the digits are transposed. 4 may become 2 and so on. Press F5 over and over, you get the idea. 
OK, I can see that the number of givens stays the same and so is the symmetry. Given that, does that mean each version is of equal difficulty and has a similar solution path? 

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keith
Joined: 19 Sep 2005 Posts: 3284 Location: near Detroit, Michigan, USA

Posted: Fri May 31, 2013 8:41 pm Post subject: 


Marty R. wrote:  Quote:  Now, press F5 to refresh the page. You will see what I think is the same puzzle, except some of the digits are transposed. 4 may become 2 and so on. Press F5 over and over, you get the idea. 
OK, I can see that the number of givens stays the same and so is the symmetry. Given that, does that mean each version is of equal difficulty and has a similar solution path? 
It's the same puzzle, only the symbols (numbers) are interchanged.
Keith 

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