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VH+ 071421 Nice example

 
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immpy



Joined: 06 May 2017
Posts: 455

PostPosted: Wed Jul 14, 2021 6:36 pm    Post subject: VH+ 071421 Nice example Reply with quote

Hello all, enjoy the puzzle...

Code:

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

Play this puzzle online at the Daily Sudoku site

cheers...immp
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Mogulmeister



Joined: 03 May 2007
Posts: 888

PostPosted: Thu Jul 15, 2021 6:02 pm    Post subject: Reply with quote

Very nice Immp.



Quote:

UR <15> in r36 c13. You can remove both 5's on r6c13 This means r6c2 has to be 5 and puzzle is solved.
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immpy



Joined: 06 May 2017
Posts: 455

PostPosted: Thu Jul 15, 2021 11:58 pm    Post subject: Reply with quote

Yes Mogulmeister. Not being critical, please take no offense, but I believe you have actually used the Hidden Rectangle on those cells to remove the 5 from each. And that works very well indeed. The beauty for me was that that set of cells was a Type 3 UR. And I need a refresher on the higher types occasionally.
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immpy



Joined: 06 May 2017
Posts: 455

PostPosted: Fri Jul 16, 2021 12:18 am    Post subject: Reply with quote

After basics grid:

Code:

+---------------+------------+----------------+
| 46   7   469  | 28   3  28 | 69   1    5    |
| 8    3   69   | 1    5  4  | 2679 267  269  |
| 15   2   15   | 7    9  6  | 8    3    4    |
+---------------+------------+----------------+
| 7    4   26   | 3    68 1  | 5    9    268  |
| 9    68  3    | 5    4  28 | 1    268  7    |
| 1256 568 1256 | 268  7  9  | 236  4    2368 |
+---------------+------------+----------------+
| 456  9   4567 | 468  2  3  | 67   5678 1    |
| 3    56  8    | 69   1  7  | 4    256  269  |
| 246  1   2467 | 4689 68 5  | 3679 678  3689 |
+---------------+------------+----------------+

Play this puzzle online at the Daily Sudoku site

The type 3 UR uses the extra candidates in r6c13 (in this case 2 and 6) to act as a pseudo cell within the houses; in this case Row 6 and Box 4. There then becomes a Naked Quad of 2368 in Row 6, and a Naked Pair of 26 in Box 4. This allows the elimination of 68 in r6c2 and solves the puzzle in a like manner to your method. One could also eliminate the 6 in r5c2.

So...UR Type 3: 1/5 in r3c13,r6c13=>r6c2<>6,r6c2<>8.

Love those URs, cheers...immp
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immpy



Joined: 06 May 2017
Posts: 455

PostPosted: Fri Jul 16, 2021 12:22 am    Post subject: Reply with quote

It's nice to have the Hidden Rectangle Technique as a backup in case you forget or are unfamiliar with the various UR Types.
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immpy



Joined: 06 May 2017
Posts: 455

PostPosted: Fri Jul 16, 2021 12:44 am    Post subject: Reply with quote

My apologies to you Mogulmeister, yours was the Type 4 UR, in which the 5 is indeed eliminated from r6c13. See what I mean about some of these higher Type URs. Hard for me to keep them straight and in working order at all times. Again, apologies, hope you understand.

cheers...immp
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Mogulmeister



Joined: 03 May 2007
Posts: 888

PostPosted: Fri Jul 16, 2021 5:46 am    Post subject: Reply with quote

Many Thanks for the identification of the UR Immp. Absolutely agree about the many types. Im afraid I have never learned which UR type classification is which because I just tend to see them all as uniqueness tests. Rather than look to see a particular pattern, I first try and see the 4 <xy> candidates. <15> in this case.. I then tend to look at the thing empirically by plugging in a number to see if I can create the deadly pattern. On URs I tend to be plug-in and play. Empirical.

Eliminations to my mind are made on or off the UR. Sometimes it is a candidate outside the UR that is eliminated but-for me- majority of cases cause inside eliminations. This was a very powerful UR because both 5s in the floor of the UR caused the DP and they could both be eliminated.

No offence ever taken Immp. Always happy to learn something . Amazing how many URs there are now. Are we up to 6 or 7 different types now ?
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immpy



Joined: 06 May 2017
Posts: 455

PostPosted: Fri Jul 16, 2021 2:33 pm    Post subject: Reply with quote

There are six types that I am aware of. Type 1 and Type 2 are the easiest to implement. It is the presence of several extra candidates that becomes the staple of the higher types. In reference to some of our recent posted puzzles, we have of late covered Type 6, and now Types 3 and 4. All we need now is a Type 5 variety. Does anyone remember the parameters of that type? I need a reminder...
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Mogulmeister



Joined: 03 May 2007
Posts: 888

PostPosted: Fri Jul 16, 2021 3:20 pm    Post subject: Reply with quote

Immp

I found this which also has an example of a type 5

https://www.sudokuonline.io/tips/sudoku-unique-rectangle
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immpy



Joined: 06 May 2017
Posts: 455

PostPosted: Fri Jul 16, 2021 5:15 pm    Post subject: Reply with quote

Thank you Mogulmeister for the Type 5 illustration. Great refresher! Now that we have reviewed them, I can begin anew the process of slowly forgetting how to implement them. Smile The Hidden Rectangle will save the day in many of these cases.

cheers...immp
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Mogulmeister



Joined: 03 May 2007
Posts: 888

PostPosted: Fri Jul 16, 2021 5:19 pm    Post subject: Reply with quote

Yes - going back to first principles will do it
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