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Aug 17 VH

 
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS

PostPosted: Sun Aug 17, 2008 3:19 pm    Post subject: Aug 17 VH Reply with quote

An xy-wing solves R3C9 and the puzzle.

Earl


Code:

+-----------+-------------+------------+
| 8 7   5   | 4   12   9  | 12  3   6  |
| 4 1   3   | 27  6    5  | 9   27  8  |
| 9 26  26  | 3   78   18 | 57  4   15 |
+-----------+-------------+------------+
| 3 4   7   | 8   5    2  | 6   1   9  |
| 6 5   1   | 79  79   3  | 4   8   2  |
| 2 9   8   | 1   4    6  | 3   5   7  |
+-----------+-------------+------------+
| 5 268 269 | 269 1289 4  | 127 279 3  |
| 7 268 4   | 269 3    18 | 25  29  15 |
| 1 23  239 | 5   29   7  | 8   6   4  |
+-----------+-------------+------------+

Play this puzzle online at the Daily Sudoku site
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sun Aug 17, 2008 3:34 pm    Post subject: Reply with quote

Basics did it for me, I just never got to a point where I needed to look for anything.
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sdq_pete



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

PostPosted: Sun Aug 17, 2008 3:55 pm    Post subject: Reply with quote

I reached the following position:
Code:

+-----------+-------------+------------+
| 8 7   5   | 4   12   9  | 12  3   6  |
| 4 1   3   | 27  6    5  | 9   27  8  |
| 9 26  26  | 3   178  18 | 157 4   15 |
+-----------+-------------+------------+
| 3 4   7   | 8   5    2  | 6   1   9  |
| 6 5   1   | 79  79   3  | 4   8   2  |
| 2 9   8   | 1   4    6  | 3   5   7  |
+-----------+-------------+------------+
| 5 68  269 | 269 1289 4  | 127 279 3  |
| 7 268 4   | 269 3    18 | 125 29  15 |
| 1 3   29  | 5   29   7  | 8   6   4  |
+-----------+-------------+------------+

Play this puzzle online at the Daily Sudoku site

and an XYZ based in Block 9 finished it off.

Peter
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Wendy W



Joined: 04 Feb 2008
Posts: 144

PostPosted: Sun Aug 17, 2008 6:09 pm    Post subject: Reply with quote

I did it exactly the way that Peter did: xyz on 125. Puzzle was very straightforward today.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sun Aug 17, 2008 6:56 pm    Post subject: Reply with quote

Marty found that only basics were needed - so it is not a VH. I often find it hard to take the basics to their limit. In this one, I happened to see a Type 4 UR which saved the trouble.
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sdq_pete



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

PostPosted: Sun Aug 17, 2008 7:50 pm    Post subject: Reply with quote

By the way, I noticed later that in the position I posted, there is an X-wing on 1's (rows 1 and 7). And
Quote:
Marty found that only basics were needed - so it is not a VH

Possibly. It's also possible that Marty made a (lucky) mistake. What do you reckon Marty?

Peter
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sun Aug 17, 2008 8:29 pm    Post subject: Reply with quote

Quote:
Possibly. It's also possible that Marty made a (lucky) mistake. What do you reckon Marty?

Marty: Is this possible? I took you at your word!!
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania

PostPosted: Sun Aug 17, 2008 8:59 pm    Post subject: Daily Sudoku: Sun 17-Aug-2008 VH Reply with quote

UR {2,6} in r37c23. 2 in r9c5 leads to a deadly pair {2,6} in Box 1 and Box 7 leaving 9 as the only candidate in r9c5 solving the puzzle.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sun Aug 17, 2008 10:04 pm    Post subject: Reply with quote

cgordon wrote:
Quote:
Possibly. It's also possible that Marty made a (lucky) mistake. What do you reckon Marty?

Marty: Is this possible? I took you at your word!!

I appreciate your confidence in my integrity. And yes, it's possible. Is it probable ? I don't know.

I retried it and couldn't finish it with basics. Lucky mistake? Could be. What are the odds that a mistake leads to a valid solution? I don't know that either. And I'm not implying that I don't make mistakes, because my sizable eraser budget says that I do.

Is it possible that on my first attempt I happened to do things in a particular sequence that allowed my basics-only solution? Another I don't know. This is not the first time I finished a puzzle with basics where I couldn't replicate the results on the retry.

No answers, just questions.

Question Question Question
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Mon Aug 18, 2008 2:27 am    Post subject: Reply with quote

There was an x-wing on 1 in columns 6 & 9
There was an x-wing on 5 in columns 7 & 9
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills

PostPosted: Mon Aug 18, 2008 3:53 am    Post subject: Reply with quote

We seem to have a variety of code sets after basics. The codes from Earl and Peter are different, Marty solved the puzzle, and mine is similar to Peter's but with the <29> in r7c5 deleted by the <269> subset in box 8. Also, I have an additional candidate <2> in r7c2 , which is apparently like Clement has, to form a Type 4 UR on <26> in r37c23.

Code:

 *--------------------------------------------------*
 | 8    7    5    | 4    12   9    | 12   3    6    |
 | 4    1    3    | 27   6    5    | 9    27   8    |
 | 9    26   26   | 3    178  18   | 157  4    15   |
 |----------------+----------------+----------------|
 | 3    4    7    | 8    5    2    | 6    1    9    |
 | 6    5    1    | 79   79   3    | 4    8    2    |
 | 2    9    8    | 1    4    6    | 3    5    7    |
 |----------------+----------------+----------------|
 | 5    268  269  | 269  18   4    | 127  279  3    |
 | 7    268  4    | 269  3    18   | 125  29   15   |
 | 1    3    29   | 5    29   7    | 8    6    4    |
 *--------------------------------------------------*


Clement wrote:
UR {2,6} in r37c23. 2 in r9c5 leads to a deadly pair {2,6} in Box 1 and Box 7 leaving 9 as the only candidate in r9c5 solving the puzzle.

Clement, I do not understand your deletion. Given my code, a <2> in r9c5 will make a <26> bivalue in r7c3, but you will still have the third candidate, a <8>, in r7c2. Would you please explain your logic.

For me, the UR <26> deleted <2> from r7c2 due to the strong link on <6> in col3.

Also a second Type 4 UR on <15> exists inr38c79 that deletes 1 from r38c7 but again that does not solve the puzzle.

After clean-up and finding a useless kite on <1>, I finally found the killer XYZ in box 9.

Ted
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Wendy W



Joined: 04 Feb 2008
Posts: 144

PostPosted: Mon Aug 18, 2008 6:38 pm    Post subject: Reply with quote

Marty, that has happened to me many times. It it all depends on the sequence of methods you use. I used to follow the same sequence like clockwork: after basics I'd look for x-wings, then I'd move on to xy's and xyz's. Recently I've been looking for xy's and xyz's first just because they're more fun. I used to fill in the basics using rows; sometimes now I'll do columns or boxes.
Vive la difference.
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sdq_pete



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

PostPosted: Mon Aug 18, 2008 7:53 pm    Post subject: Reply with quote

If a cell has two candidates and you jump (unknowingly) to a conclusion about the definitive value, then you have a 50% chance of being right.

Be that as it may, perhaps Wendy's remark is the chance I was looking for to make a little remark about the X techniques. I don't know how others experience it, but I find the ease of spotting X patterns to be - generally speaking - in inverse proportion to the complexity. Thus I generally find XYZ's the easiest to spot; then XY, then X-wings.
I guess this has to do with the degree of constraint: the XYZ is a highly constrained pattern - for an XYZ to be possible, there first has to be a triple and a subset bivalue within one block; only then need you look for a third bivalue outside that block.
X-wings I generally find difficult to spot, despite the logic of the pattern being simple. XY's ought to be easy to spot, but sometimes there are just so many bivalues hanging around, it's like looking for a needle in a haystack.
And of course, in a randomly generated puzzle, the more complex the pattern the less likely it is to occur, presumably.

Just wanted to get that off my chest.

Peter
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Mon Aug 18, 2008 9:03 pm    Post subject: Reply with quote

Quote:
but I find the ease of spotting X patterns to be - generally speaking - in inverse proportion to the complexity.

What's the opposite of "inversely proportional" - directly proportional? - can't remember - but I'm one of them. For me, X-wings are simple square patterns - so much easier than looking for those "needle in haystack" xy nos. But each to his own eh!
But while we are on techniques, I have noticed a recent trend towards more and more complex techniques - eg hybrid solutions - an ER + an xy wing (or something like that). Maybe they were always there and I hadn't paid attention. Either way, they transcend my level of "fun".
That's off my chest.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Mon Aug 18, 2008 9:32 pm    Post subject: Reply with quote

Quote:
What's the opposite of "inversely proportional" - directly proportional?

As far as I'm concerned, it is.

Like Wendy and Pete, I'll look for XY, XYZ, W, M-Wings, URs, ERs, and almost anything else before checking for X-Wings because I despise looking for them for reasons that I don't fully understand.
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DennyOR



Joined: 12 Sep 2007
Posts: 33
Location: Portland, Oregon

PostPosted: Thu Aug 21, 2008 10:54 pm    Post subject: Reply with quote

X-wings are first to try on my official list of advanced techniques, probably because that was the first advanced technique I learned, but also because they're pretty useful. In practice I usually look for other things first because X-wings are tedious, especially if you think you ought to be looking for finned X-wings and swordfish at the same time.

I think the most tedious part of a sudoku is getting to the stage where you can begin to use advanced techniques, so, after having to do all that work, I prefer a puzzle where I need to find two or more advanced techniques to solve it. I'd also like to see the very hards get gradually harder over time (which they may be).

I've often thought that the ideal sudoku puzzles would be ones that are pre-completed up to the point where advanced techniques are required.
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Wendy W



Joined: 04 Feb 2008
Posts: 144

PostPosted: Fri Aug 22, 2008 8:04 pm    Post subject: Reply with quote

Denny, that's an interesting thought, but for me doing the basics gets me "acquainted" with the day's puzzle in a way that just starting with advanced techniques wouldn't. It's part of the ritual. By doing the basics, you get a sense without consciously realizing it what numbers are predominating, which boxes are going to be a problem, that sort of thing.
x-wing was the 1st advanced technique I learned, too, but I've recently been learning the many adjunctive benefits of xy's and xyz's -- for instance, spotting naked triples.
Sudoku is not about the end result; it's about the process.
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Kdelle



Joined: 20 Mar 2008
Posts: 59
Location: Hudson, NH

PostPosted: Fri Aug 22, 2008 10:13 pm    Post subject: Reply with quote

Denny,

I agree...and therein lies the beauty of the "sweep" function. At least the most tedious work is done!

I like "auto pencilmarks" at BB...but even their Super Hards are not as difficult for me as some of the Very Hards on this site.

I do think I'm getting spoiled, though. Like Wendy said, if you do it all right from the beginning, you get a sense of the puzzle.

I'm curious as to how many of us use the "Sweep" and "Auto pencilmarks" to get to the meat of the game.

Kathy
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wapati



Joined: 10 Jun 2008
Posts: 472
Location: Brampton, Ontario, Canada.

PostPosted: Sat Aug 23, 2008 4:29 am    Post subject: Reply with quote

DennyOR wrote:

I think the most tedious part of a sudoku is getting to the stage where you can begin to use advanced techniques,


I look for x-wings and URs as I fill in, I often spot them and mark cells as "-" whatever candidates.
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DennyOR



Joined: 12 Sep 2007
Posts: 33
Location: Portland, Oregon

PostPosted: Sun Aug 24, 2008 4:44 am    Post subject: Reply with quote

I print out the sudokus and do them on paper. That's probably very old-fashioned of me.
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