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NoName Puzzle 7

 
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Tue Jan 27, 2009 4:03 pm    Post subject: NoName Puzzle 7 Reply with quote
This puzzle is from my Salsa file, but it doesn't meet the difficulty level desired.

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

Play this puzzle online at the Daily Sudoku site

===== ===== ===== ===== ===== ===== ===== ===== ===== Ratings

Can be solved using steps from ...

Basics: Naked/Hidden Single, Naked Pair/Triple, Locked Candidate 1/2

Basics+: Naked Quad, Hidden Pair/Triple/Quad

VH: BUG+1, UR Type 1, X-Wing, XY-Wing, XYZ-Wing

VH+: 2-String Kite, Empty Rectangle, Remote Pair, Skyscraper, Colors, UR Type 2

Advanced: finned/Sashimi X-Wing, Multiple Colors, Swordfish, M-Wing, W-Wing, XY-Chain

Extreme: Jellyfish, (but mostly) Chain
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wapati



Joined: 10 Jun 2008
Posts: 472
Location: Brampton, Ontario, Canada.
PostPosted: Tue Jan 27, 2009 6:47 pm    Post subject: Reply with quote
This might be a one stepper, I just don't know what to consider it.
Is it a nice loop?

Code:
.--------------.--------------------.---------------.
| 7  9    4    | 3        6     2   | 15 a*15    8  |
| 1  3    8    | 579      7-5   579 | 4    6     2  |
| 5  2    6    | 8        1     4   | 7    9     3  |
:--------------+--------------------+---------------:
| 8  145  1257 | 6        3     157 | 25   247-5 9  |
| 3  145  1257 | 2457     9     157 | 6    8     45 |
| 9  6    257  | 2457     247-5 8   | 3    247-5 1  |
:--------------+--------------------+---------------:
| 4  7    159  | 59-2-5 e*25    3   | 8  b*12    6  |
| 6  15   159  | 2479-5   8     79-5| 12   3     45 |
| 2  8    3    | 1      d*45    6   | 9  c*45    7  |
'--------------'--------------------'---------------'


The 5 cells shown as a-e eliminate the marked candidates and leave the puzzle easy. Is this 3 xy-chains or one pattern whose name I don't know?
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Tue Jan 27, 2009 11:15 pm    Post subject: Reply with quote
wapati wrote:
This might be a one stepper, I just don't know what to consider it. Is it a nice loop?

The 5 cells shown as a-e eliminate the marked candidates and leave the puzzle easy. Is this 3 xy-chains or one pattern whose name I don't know?

It's called an XY-Loop. It occurs when the endpoints of an XY-Chain reside in the same house/unit.

Code:
 like this XY-Loop
 +-----------------------------------------------------------------------+
 |  7      9      4      |  3      6      2      |  15     15     8      |
 |  1      3      8      |  579    57     579    |  4      6      2      |
 |  5      2      6      |  8      1      4      |  7      9      3      |
 |-----------------------+-----------------------+-----------------------|
 |  8      145    1257   |  6      3      157    | a25     2457   9      |
 |  3      145    1257   |  2457   9      157    |  6      8     e45     |
 |  9      6      257    |  2457   2457   8      |  3      2457   1      |
 |-----------------------+-----------------------+-----------------------|
 |  4      7      159    |  259    25     3      |  8      12     6      |
 |  6     c15     159    |  24579  8      579    | b12     3     d45     |
 |  2      8      3      |  1      45     6      |  9      45     7      |
 +-----------------------------------------------------------------------+
 # 59 eliminations remain
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
PostPosted: Wed Jan 28, 2009 1:57 pm    Post subject: Reply with quote
I solved this fun and interesting puzzle in my normal many-steps approach using five different wings as follows.
Quote:
xy-wing125
x-wing5
xy-wing179
a repeat of the xy-wing125 with pincer transport
w-wing15 with pincer transport

daj95376 wrote:
.
It's called an XY-Loop. It occurs when the endpoints of an XY-Chain reside in the same house/unit.

Danny, is this pattern called a "forcing loop" by Susser?

Ted
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Wed Jan 28, 2009 4:32 pm    Post subject: Reply with quote
tlanglet wrote:
Danny, is this pattern called a "forcing loop" by Susser?

I'm no expert on names for techniques, but I can certainly see where someone would use that name. When I visualize what's happening, I see it as a Double Implication/Forcing Chain (that could loop back onto itself). This is the only way that I can be certain that I've caught all of the eliminations.

As a side-note, wapati's observation led me to realize that it'd be trivial for me to update my solver to flag XY-Loops when processing XY-Chains.
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