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A VH from The Times

 
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Sun Jul 06, 2008 11:30 am    Post subject: A VH from The Times Reply with quote

The super-fiendish from last Thursday makes a passable, if straightforward, VH:

Code:
+-------+-------+-------+
| . 9 . | . . . | . 5 4 |
| . . 2 | . . . | 3 . . |
| 4 . . | . 7 3 | 9 . . |
+-------+-------+-------+
| . . . | . 8 7 | 1 . . |
| 7 . . | . 4 . | . . 2 |
| . . 1 | 3 2 . | . . . |
+-------+-------+-------+
| . . 8 | 4 5 . | . . 9 |
| . . 9 | . . . | 2 . . |
| 6 5 . | . . . | . 4 . |
+-------+-------+-------+
The Times No. 1994

A printable version can be found here.

Steve
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Marty R.



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

PostPosted: Sun Jul 06, 2008 4:52 pm    Post subject: Reply with quote

I used an XY-Wing with pincer coloring, an XYZ-Wing and an ER. It's possible that the ER would have been enough had I done it first.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Sun Jul 06, 2008 5:58 pm    Post subject: Reply with quote

This being the Times, the puzzle must yield to either x-wing or swordfish.
And, lo and behold, there is a swordfish ("6" in columns 3,6 and 7, rows 1,5, and 7), which solves the puzzle

There is a kite, too (in "7", row 1/col 2 removes 7 from r7c7)
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tlanglet



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

PostPosted: Sun Jul 06, 2008 8:39 pm    Post subject: Reply with quote

nataraj wrote:


There is a kite, too (in "7", row 1/col 2 removes 7 from r7c7)


Nataraj,
I did not see the kite, but noticed a finned x-wing in r19c37 that deleted the <7> in r9c9 thereby providing an x-wing in r19c37 which deleted the <7> from r7c7 that, as you noted, finished the puzzle.

Ted
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Mon Jul 07, 2008 1:02 pm    Post subject: Reply with quote

Three good solutions.

I’m not sure they quite qualify as VH, though. Just to show I wasn’t cheating, this is where the going gets harder.

Code:
+---------------------------------------------+
| 138 9   367 | 1268 16  126  | 678 5    4    |
| 18  167 2   | 5    9   4    | 3   1678 1678 |
| 4   16  5   | 168  7   3    | 9   2    168  |
-----------------------------------------------
| 5   2   4   | 69   8   7    | 1   369  36   |
| 7   368 36  | 169  4   169  | 5   689  2    |
| 9   68  1   | 3    2   5    | 4   678  678  |
-----------------------------------------------
| 2   137 8   | 4    5   16   | 67  1367 9    |
| 13  4   9   | 7    136 8    | 2   136  5    |
| 6   5   37  | 29   13  29   | 78  4    1378 |
+---------------------------------------------+


The X-Wing on 7 in rows 1 and 9 eliminates 7 from r7c7 and overcomes the difficulty.

Steve
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Marty R.



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

PostPosted: Mon Jul 07, 2008 3:57 pm    Post subject: Reply with quote

Quote:
The X-Wing on 7 in rows 1 and 9 eliminates 7 from r7c7 and overcomes the difficulty.

My ER did the same thing, with the ERI in r7c3 and the 7 being eliminated from r7c7.
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Deposit



Joined: 07 Jul 2008
Posts: 1
Location: United Kingdom

PostPosted: Tue Jul 08, 2008 7:26 am    Post subject: "The Times" Sudoku Super Fiendish No.1994 Reply with quote

I am fascinated by the methods for solution of this puzzle. Shocked I reached the point where visual inspection finished (like Steve R.) and then played scenarios. Since R9C4 and R9C6 are mutually exclusively 2 or 9, this feature is the only way in. If... r9c4 is 2 and if r5c6 is 1 then it doesn't work; you get double 6s or 7s in one column. But If... r9c4 is 2 and r5c4 is 1 then it all works. R5c4 and r5c6 form another half-mutually exclusive pair where one of them is 1, but the other can be something different. I don't like using "If..." as only one solution fits the puzzle and so it should be possible to spot one option...? Confused
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Tue Jul 08, 2008 8:47 am    Post subject: Reply with quote

Steve R wrote:
Three good solutions.

I’m not sure they quite qualify as VH, though.


Strictly speaking, none of the solutions falls under the x-wing or xy(z)-wing rule that seems to define "very hard" here.

a) The swordfish (6) is similar to x-wing but it uses three rows and 3 columns.

b) The kite (7) employs the same principle as the x-wing, but the strong links are perpendicular and not parallel.

c) The "x-wing" (7) is not a simple x-wing but a finned creature, because r9c9 contains a "7" as well. But if r9c9 were 7, then r7c7 could not be 7, and this argument indeed "overcomes the difficulty".

Myself, I tend to just take good solutions and not to worry too much about qualifications. Don't worry, be happy

Very Happy
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Tue Jul 08, 2008 10:50 am    Post subject: Reply with quote

You’re right: the x-wing in r19 is finned so I did cheat when I claimed the puzzle was VH.

I did it on the day it was published and was so sure it was a classical x-wing when I submitted the post that I failed to check the diagram. Perhaps this is the penalty for not distinguishing between finned and classical in my own mind.

The earlier solutions were not only good: they were just as close to VH as mine. Apologies to all for suggesting otherwise.

Steve
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