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Steve R
Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England
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 Posted: Sun Jul 06, 2008 11:30 am Post subject: A VH from The Times |
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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
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| Posted: Sun Jul 06, 2008 4:52 pm Post subject: |
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| 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
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| Posted: Sun Jul 06, 2008 5:58 pm Post subject: |
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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
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| Posted: Sun Jul 06, 2008 8:39 pm Post subject: |
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| 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
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| Posted: Mon Jul 07, 2008 1:02 pm Post subject: |
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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
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| Posted: Mon Jul 07, 2008 3:57 pm Post subject: |
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| 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
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| Posted: Tue Jul 08, 2008 7:26 am Post subject: "The Times" Sudoku Super Fiendish No.1994 |
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I am fascinated by the methods for solution of this puzzle.  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...?  |
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Tue Jul 08, 2008 8:47 am Post subject: |
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| 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
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Steve R
Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England
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| Posted: Tue Jul 08, 2008 10:50 am Post subject: |
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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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