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April 14 VH

 
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Mon Apr 14, 2008 6:03 am    Post subject: April 14 VH Reply with quote
This one takes off at breathtaking speed. Almost no resistance and definitely very few pencil marks needed. After sweeping the floors and dusting the towers, just looking at those houses with 6 or 7 solved cells fills up the puzzle very quickly.

When I started looking around for wings, I stumbled over this "extended" xy-wing: {8,1} - (13-32) - {2,8}, which removed 8 from r6c9 and solved the puzzle. Probably tons of other ways to do it (at least one x-wing which I only saw now, "after the fact". With so many solved cells I start looking for xy-wings first)

Grid after basics:
Code:

+--------------------------+--------------------------+--------------------------+
| 9       13      23       | 6       4       123      | 7       8       5        |
| 18      4       238      | 23      7       5        | 12      6       9        |
| 5       7       6        | 9       8       12       | 12      3       4        |
+--------------------------+--------------------------+--------------------------+
| 6       13      358      | 4       15      23       | 9       7       28       |
| 7       2       4        | 8       6       9        | 5       1       3        |
| 18      9       358      | 23      15      7        | 6       4       28       |
+--------------------------+--------------------------+--------------------------+
| 2       8       9        | 7       3       6        | 4       5       1        |
| 4       6       1        | 5       9       8        | 3       2       7        |
| 3       5       7        | 1       2       4        | 8       9       6        |
+--------------------------+--------------------------+--------------------------+
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andras



Joined: 31 Oct 2007
Posts: 56
Location: Mid Wales
PostPosted: Mon Apr 14, 2008 8:17 am    Post subject: Reply with quote
There's a simple xy on 1,5,8 (pivot at R4C3) which I think is all that's needed to break it, though there's also an x-wing on 3 which I found first but probably isn't really needed.

Yes indeed, a very quick-solving puzzle. Nice to see the VH puzzles back Smile

John
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Mon Apr 14, 2008 10:33 am    Post subject: Reply with quote
X-wing on <3> reveals an XY-wing <15>.

Keith
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melis



Joined: 04 Feb 2008
Posts: 6
Location: Berkshire, England
PostPosted: Mon Apr 14, 2008 10:40 am    Post subject: Reply with quote
Ditto for me, x-wing on 3 that reveals an xy-wing to solve the puzzle. A nice way to start the week!
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Mon Apr 14, 2008 12:59 pm    Post subject: april 14 vh Reply with quote
There is also a Bug+1 in box 4.

Earl
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada
PostPosted: Mon Apr 14, 2008 1:16 pm    Post subject: Reply with quote
The x-wing on <3> left a triple <835> in C3.
I'm not into Bugs+1 but the <835> in R6C3 was the only three digit no. left. Since this formed an xyz, xy, xz triple in C3, I took the x or <8> out of R6C3. I know you do this for Bugs+1 when the xyz is in a box - but can you do it in a column or row? It worked but maybe that was luck.
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
PostPosted: Mon Apr 14, 2008 7:58 pm    Post subject: Reply with quote
Craig,

In a BUG+1 the extra digit will always occur three times in a row, a column, and a box. That was the case here.
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania
PostPosted: Mon Apr 14, 2008 8:23 pm    Post subject: Daily Sudoku: Mon 14-Apr-2008 VH Reply with quote
Can also be solved by Aligned Pair Exclusion (APE). Consider the possible pairs in r4c2{1,3} and r4c3{5,8} which are 15,18,35,38, these CANNOT duplicate the contents of the cells in r6c1{1,8} and r4c5{1,5} leaving 3 in r4c2 which solves the puzzle.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Mon Apr 14, 2008 8:28 pm    Post subject: Reply with quote
Clement,

this is amazing. I've never met anyone actually using this technique in a regular puzzle. Honorable mention in my book of all time sophisticated puzzlers! Very Happy
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada
PostPosted: Mon Apr 14, 2008 10:14 pm    Post subject: Reply with quote
Quote:
I've never met anyone actually using this technique in a regular puzzle.

Hold on there old chap!! Some weeks ago (Marty was it?) gave a solution and explanation for APEs. It so impressed me, I added it to my Folder of Favourite Solutions. To be honest though, I've since found them painfully rare and hard to find.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Tue Apr 15, 2008 12:04 am    Post subject: Reply with quote
cgordon wrote:
Quote:
I've never met anyone actually using this technique in a regular puzzle.

Hold on there old chap!! Some weeks ago (Marty was it?) gave a solution and explanation for APEs. It so impressed me, I added it to my Folder of Favourite Solutions. To be honest though, I've since found them painfully rare and hard to find.

I was excited when I first learned APEs, but then it was pointed out to me that almost all of them overlap with XY- or XYZ-Wings, so the technique doesn't benefit me much except in those few cases when I miss the Wing but notice the APE.

Of course, the aforementioned one is also an XY-Wing.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741
PostPosted: Tue Apr 15, 2008 12:32 am    Post subject: Reply with quote
cgordon wrote:
Quote:
I've never met anyone actually using this technique in a regular puzzle.

Hold on there old chap!! Some weeks ago (Marty was it?) gave a solution and explanation for APEs. It so impressed me, I added it to my Folder of Favourite Solutions. To be honest though, I've since found them painfully rare and hard to find.


if you find that APE is painful, then I direct your attention to the Almost Locked Set - ALS Rolling Eyes, then you will count subsets til the cows come home. Laughing

xy-wings, xyz-wings, wxyz -wings are all forms of APEs. in fact, they are just a subset of APEs.

although an xy-wing is a subset of an xy-chain, it does not mean that an xy-chain is a subset of APE. the coincidence is just another twist in sudoku life.

the discussion on w-wings, m-wings and chains combining techniques with other patterns has actually dissuaded me from looking for APE.
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