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Puzzle 11/04/26: B Moderate BBDB

 
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Apr 27, 2011 2:17 pm    Post subject: Puzzle 11/04/26: B Moderate BBDB Reply with quote

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

Play this puzzle online at the Daily Sudoku site
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peterj



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

PostPosted: Thu Apr 28, 2011 7:31 am    Post subject: Reply with quote

I found this one pretty tough for a "moderate"! A slightly daunting grid; I needed a chain, admittedly short, and a bunch of not-so-easy-to-spot turbot moves...
Quote:
xy-chain ; (6=1)r8c7 - (1=9)r7c7 - (9=2)r7c8 - (2=6)r2c6 ; r13c7<>6
er(2) b1, c4 ; r6c1<>2
kite(6) r6, c8 ; r2c1<>6
kite(6) c1, r4 ; r3c6<>6
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Thu Apr 28, 2011 9:20 am    Post subject: Reply with quote

Yes, I've been thinking that a single 4-cell XY-Chain may not qualify as Moderate. I originally started placing them in the Moderate category because "XY-Wing with an extension" was being used so often to solve puzzles that I'd classified as Difficult. Now, I'm not sure how to classify puzzles that need one 4-cell XY-Chain.

Those that need 2x 4-cell XY-Chains are classified as Difficult. In fact, the Difficult+ puzzle with the same date has a 5-cell XY-Chain and a 4-Cell XY-Chain in my solver's solution. Which might explain the difficult you and Ted had finding a single-stepper solution for it.
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peterj



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

PostPosted: Thu Apr 28, 2011 5:27 pm    Post subject: Reply with quote

daj95376 wrote:
Now, I'm not sure how to classify puzzles that need one 4-cell XY-Chain.

I agree that 4-cell xy-chains are much less difficult than longer xy-chains or general AIC chains. I think the other aspect though is the order and timing of moves. If the first meaningful move in the puzzle is a chain and it comes after short basics on a relatively crowded grid - it feels harder to me. In this case the grid was quite crowded, I think there was an extraneous x-wing, but the right-hand shute drew you to the bivalues - not like some of the "extremes" where you do a couple of basics and then are faced with "losing the will to live" moment with a sea of pencilmarks... and no amount of hitting F11 in SimpleSudoku will help you Laughing

To some extent difficulty is always going to be a subjective criteria.
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Marty R.



Joined: 12 Feb 2006
Posts: 5063
Location: Rochester, NY, USA

PostPosted: Thu Apr 28, 2011 7:32 pm    Post subject: Reply with quote

I also found this more difficult than a moderate. I used a chain, 37 UR and Medusa.

The chain started with the 36 in r1c7. I started with the 6 and it ended up proving a 3 in the same cell. That's the second time this week that one value in a cell proved the other value in the same cell.

Is this just one of the typical outcomes of a chain or does this have its own name?
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