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Puzzle 11/08/09: ~ Advanced BBDB w/fish

 
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Tue Aug 09, 2011 9:31 pm    Post subject: Puzzle 11/08/09: ~ Advanced BBDB w/fish Reply with quote

My solver even used the kitchen sink trying to solve this puzzle at the Advanced rating.

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

Play this puzzle online at the Daily Sudoku site
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peterj



Joined: 26 Mar 2010
Posts: 974
Location: London, UK

PostPosted: Wed Aug 10, 2011 8:34 am    Post subject: Reply with quote

Ouch! Well, this goes in a file marked "extreme" for me (It was also an SE7.8 which seems high for an Advanced Exclamation )
I did throw the kitchen sink at it - but still got nowhere. Finally the "fish" hint steered me towards x-chains and this was my best path in the end (after more than an hour)...
Code:
x-chain(5) (5)r3c1=r1c3 - r1c6=r9c6 - r9c2=r46c2 ; r46c1<>5
ur(24)[(7)r4c8=(5)r4c3] - (5=2)r6c2 - (2=7)rc6 ; r4c5<>7, r6c9<>7
x-chain(2) (2)r6c9=r6c2 - r9c2=r9c6 - r2c6=r79c2 ; r3c9<>2

Look forward to seeing an Advanced solution. Smile
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Aug 10, 2011 4:31 pm    Post subject: Reply with quote

The title was suppose to imply that this could be solved as an Advanced rated puzzle ... if ... it wasn't for a fish/X-chain step.

Here are the steps my solver found. I did not check to see which are necessary.

Code:
 after basics
 +-----------------------------------------------------------------------+
 |  2      3      578    |  579    789    578    |  6      1      4      |
 |  1      9      78     |  6      4      2378   |  2378   5      2378   |
 |  578    4      6      |  2357   2378   1      |  23789  279    2378   |
 |-----------------------+-----------------------+-----------------------|
 |  59     125    1245   |  8      237    6      |  12379  2479   2357   |
 |  6      7      1248   |  23     5      9      |  1238   24     238    |
 |  589    258    3      |  4      1      27     |  2789   6      2578   |
 |-----------------------+-----------------------+-----------------------|
 |  4      128    12789  |  12379  23789  2378   |  5      27     6      |
 |  578    6      12578  |  1257   278    4      |  27     3      9      |
 |  3      25     2579   |  2579   6      257    |  4      8      1      |
 +-----------------------------------------------------------------------+
 # 113 eliminations remain

   c1b9  turbot fish/ER                  <> 7    r3c8

   c8b5  turbot fish/ER                  <> 7    r7c6

(5)r3c1 = r1c3 - r1c6 = r9c6 - r9c2 = (5)r46c2  =>  r46c1<>5
-or fish-
  finned Franken Swordfish c26b1\r19b4              r46c1<>5

 <57+2>  XY-Wing  r8c1/r8c7+r9c2         <> 2    r8c3
-or turbot fish for same elimination-

 r6  b3  Empty Rectangle                 <> 7    r2c6

 <47+2>  XYZ-Wing r4c8/r4c5+r5c8         <> 2    r4c79

 r45c38  <24> UR Type 4.2233             <> 2    r4c38

   c38   X-Wing                          <> 2    r7c46

 r38     X-Wing                          <> 5    r1c4

<25> RP: r3c4 - r8c4 - r9c6 - r9c2 - r6c2 - r6c9  =>  r3c9<>2

Interestingly enough, all of the listed steps are restricted to values {2,5,7}.

Yes, this puzzle could have been declared an Extreme rated puzzle !!!
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Marty R.



Joined: 12 Feb 2006
Posts: 5064
Location: Rochester, NY, USA

PostPosted: Wed Aug 10, 2011 5:17 pm    Post subject: Reply with quote

Peter, I don't know what an X-Chain is, although it appears to involve just one number. Maybe an advanced form of Simple Coloring?

At any rate, as you know, I'm notation-challenged and can't fully follow your first chain, but I can follow it from the grid. Basically, I think, if r3c1<>5, then r46c2=5, thus allowing the eliminations.

That's a very nice move, but how did you find that little isle in this ocean of poly-value cells?
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peterj



Joined: 26 Mar 2010
Posts: 974
Location: London, UK

PostPosted: Wed Aug 10, 2011 6:12 pm    Post subject: Reply with quote

daj95376 wrote:
Yes, this puzzle could have been declared an Extreme rated puzzle !!!

Danny, I even put it into Hoduko after to see if I had been stupid - you should see the mess that makes of the solution path by not playing the chain on 5s!!
Marty R. wrote:
That's a very nice move, but how did you find that little isle in this ocean of poly-value cells?

Marty, I use Simple Sudoku as my helper. I used to do simple and multi-colouring - this x-chain on 5 would need three levels of colouring though. Now I tend to look directly for x-chains/turbots. I filter on the candidate and then pick a strong link, look to see if the end can see another strong link, repeat, check for eliminations etc. Easy if using SS, not so on paper...
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Aug 10, 2011 11:17 pm    Post subject: Reply with quote

I've removed "w/fish" from the title of puzzles remaining to be posted. These puzzles have been re-labeled "XY" or "Extreme" -- as appropriate.

Regards, Danny
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