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sept 10 vh

 
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Mon Sep 10, 2007 9:58 am    Post subject: sept 10 vh Reply with quote

I found today's rather interesting in that I needed both alternating inference chains and xy-wing techniques to solve.
At some point, this is the situation in '3's, marked are strong links (rows, cols, boxes with exactly 2 occurrences) and the remaining cells with '3'.
Code:

+·····+·····+·····+
·*---*·     ·     ·
·    |·     ·     ·
·    |·     ·     ·
·    |·     ·     ·
·    |·     ·     ·
+····|+·····+·····+
·*-----*    ·     ·
·    |· \   ·     ·
·    |·  \  ·     ·
·    |·   \ ·     ·
·o * *·    *·     ·
+··|··+····|+·····+
·  |  ·    *-----*·
·  |  ·     ·    |·
·*-----*    ·    |·
· \|  ·     ·    |·
·  *  ·o    ·    *·
+·····+·····+·····+

The candidate '3' can be removed from r1c1 and r6c1(41=44-66=76-84=81),
r6c3 (continue ...81-92=62), and r9c4(92=62-66=76).
A few steps later, an xy-wing leaves naked '7' in r1c1 and the puzzle collapses.

very nice
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Mon Sep 10, 2007 11:53 am    Post subject: Reply with quote

Code:

+---------------+----------------+----------------+
| 3567 9   3578 | 468  14568 14  | 5678 568  2    |
| 1    78  2    | 9    568   68  | 3    4    5678 |
| 56   4   58   | 2    3     7   | 1568 1568 9    |
+---------------+----------------+----------------+
| 39   1   4    | 36   7     5   | 2    689  68   |
| 2    6   57   | 48   48    9   | 57   3    1    |
| 3579 378 3578 | 1    2     36  | 4    569  567  |
+---------------+----------------+----------------+
| 4    2   1    | 5    9     368 | 68   7    368  |
| 37   5   6    | 37   18    2   | 9    18   4    |
| 8    37  9    | 3467 1468  14  | 156  2    356  |
+---------------+----------------+----------------+

Play this puzzle online at the Daily Sudoku site

Interesting pattern, though I did it simply with 2 (rather easily spotted) XY wings (pivots R3C3 and then R6C6)

Peter
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Mon Sep 10, 2007 2:38 pm    Post subject: Reply with quote

thx, Peter Smile

I usually try the coloring approach first to reduce the number of candidates in the cells (also to double-check for hidden singles etc.), and only then look for xy- and w-wings.

Seeing how easy it was with xy-wing, maybe I'll re-evaluate my search pattern...
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Johan



Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium

PostPosted: Mon Sep 10, 2007 6:19 pm    Post subject: Reply with quote

There is also a one step move present that collapses the puzzle completely.

A 6-cell xy-chain starting with <8> in R2C6

[68][87][73][37][73][36], which erases both <6>'s in R1C4 and R6C6


Code:

+---------------+----------------+----------------+
| 3567 9   3578 |4-68  14568 14  | 5678 568  2    |
| 1   B78  2    | 9    568  A68  | 3    4    5678 |
| 56   4   58   | 2    3     7   | 1568 1568 9    |
+---------------+----------------+----------------+
| 39   1   4    |F36   7     5   | 2    689  68   |
| 2    6   57   | 48   48    9   | 57   3    1    |
| 3579 378 3578 | 1    2    3-6  | 4    569  567  |
+---------------+----------------+----------------+
| 4    2   1    | 5    9     368 | 68   7    368  |
|D37   5   6    |E37   18    2   | 9    18   4    |
| 8   C37  9    | 3467 146   14  | 156  2    356  |
+---------------+----------------+----------------+
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Mon Sep 10, 2007 11:04 pm    Post subject: Reply with quote

nataraj,

In your 3-grid, there is an X-Wing in R48 that eliminates R16C1 and R9C4 directly and R6C3 indirectly. The "color wings" work, but the fish is more direct.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Tue Sep 11, 2007 11:48 am    Post subject: Reply with quote

indeed. x-wing. how straightforward. Embarassed
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