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July 4 VH

 
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Earl



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

PostPosted: Sat Jul 04, 2009 3:16 am    Post subject: July 4 VH Reply with quote

No firecracker for the Fourth. Same old, same old.

Solution: 235 xy-wing does it

Early Earl


Last edited by Earl on Sat Jul 04, 2009 4:06 am; edited 1 time in total
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tlanglet



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

PostPosted: Sat Jul 04, 2009 3:40 am    Post subject: Reply with quote

Yes, it took a few minutes to complete basics and only a few seconds to finish the puzzle. However a second view provided me a more interesting one step solution:
Quote:
In r78c149 we find 259 except in r7c9 the cell has the addional digit 3. In order to prevent a DP, r7c9 must be equal to 3.

Ted
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Sat Jul 04, 2009 6:11 am    Post subject: Reply with quote

I am pretty sure the below grid has all the basic digits squeezed from it. It took me quite awhile (for some silly wrong-headed reason) to find the magical wings: 23-25-35, or 23-35-25. The middle numbers above = pivot. I bet you virtuosos finished the puzzle in a matter of a few minutes, with taking a bathroom break & getting up and getting a cup included in the total time.


Code:

+-----------+----------+------------+
| 25  8 9   | 1   4 23 | 35 6  7    |
| 4   7 235 | 8   6 23 | 9  12 1235 |
| 1   6 23  | 7   5 9  | 4  8  23   |
+-----------+----------+------------+
| 8   2 1   | 4   9 5  | 7  3  6    |
| 3   9 4   | 6   2 7  | 1  5  8    |
| 6   5 7   | 3   8 1  | 2  9  4    |
+-----------+----------+------------+
| 259 1 6   | 259 7 8  | 35 4  2359 |
| 259 3 8   | 259 1 4  | 6  7  259  |
| 7   4 25  | 259 3 6  | 8  12 1259 |
+-----------+----------+------------+

Play this puzzle online at the Daily Sudoku site
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David



Joined: 02 Jun 2006
Posts: 58
Location: Bedford, UK

PostPosted: Sat Jul 04, 2009 8:47 am    Post subject: Reply with quote

There seems to be a very large number of solutions to these puzzles using xy or xyz wings . Presumably due to the way in which they are constructed ?
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Captain Pete



Joined: 09 Jun 2007
Posts: 55
Location: Oley, PA

PostPosted: Sat Jul 04, 2009 12:17 pm    Post subject: Reply with quote

Using Crunched's grid above, in blocks 7,8, and 9 there is a pattern of six 259s with one including a 3. Can we assume that similar to a rectangle, the one including the 3 must always be a 3?
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wapati



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

PostPosted: Sat Jul 04, 2009 1:49 pm    Post subject: Reply with quote

That is a valid deduction. Good spotting.
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cgordon



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

PostPosted: Sat Jul 04, 2009 2:56 pm    Post subject: Reply with quote

Singles followed by a one-step solution - in my case an ER on <2>.
They don't get no easier!

PS. I didn't follow Captain Pete's 259 logic.


Last edited by cgordon on Sat Jul 04, 2009 3:00 pm; edited 1 time in total
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Sat Jul 04, 2009 2:57 pm    Post subject: Reply with quote

Did you see an xy or xyz wing, apart from the two xy wings that I point out above? I did not see anything else, and as I mentioned it took me quite awhile before I came up with what I did---which means that I felt as though I inspected everything before I finally found the solution. It was seemingly an especially long time because, after removing all of the basics, much of the puzzle seemed to be complete.

I don't know how these puzzles are constructed. A curious thing to me is that I never seem to be able to solve a "hard" (as opposed to "very hard") puzzle using wings. Of course wings (considered an advanced technique) are not supposed to be necessary in hard puzzles. Yet, one would expect to be able to find and use them where helpful. But I repeat: I never, never find wings in a hard puzzle.

David wrote:
There seems to be a very large number of solutions to these puzzles using xy or xyz wings . Presumably due to the way in which they are constructed ?
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tlanglet



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

PostPosted: Sat Jul 04, 2009 5:06 pm    Post subject: Reply with quote

My earlier post identified the possible DP involving the three digits 2, 5 & 9 plus a single cell, r7c9, that has the extra digit 3. This condition is similar to the Type 1 UR situation thus, as I previously noted, r7c9 must be a 3 or the puzzle would not have a single solution.

Ted
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Sun Jul 05, 2009 6:48 pm    Post subject: Reply with quote

Captain Pete wrote:
Using Crunched's grid above, in blocks 7,8, and 9 there is a pattern of six 259s with one including a 3. Can we assume that similar to a rectangle, the one including the 3 must always be a 3?


yes, this is called a MUG, multi-value universal grave.

found here.
http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=2560&sid=b1ae4b35f1151cd89b75fcec2b42fe49

the three digits have to occur in two rows, in three columns and in three boxes as you have pointed out.
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