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Swordfish

 
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Tue Feb 05, 2008 11:12 am    Post subject: Swordfish Reply with quote

Code:
 +-------+-------+-------+
 | 1 . . | 2 . . | 3 . . |
 | . 2 . | . 1 . | . 4 . |
 | . . 3 | . . 5 | . . 1 |
 +-------+-------+-------+
 | 6 . . | 1 . . | 4 . . |
 | . 7 . | . 5 . | . 1 . |
 | . . 1 | . . 7 | . . 5 |
 +-------+-------+-------+
 | 8 . . | 9 . . | 6 . . |
 | . 3 . | . 7 . | . 9 . |
 | . . 6 | . . 8 | . . 3 |
 +-------+-------+-------+ Mauricio
>>> play online
Three swordfish in the starting grid.
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Tue Feb 05, 2008 2:56 pm    Post subject: Reply with quote

oh how I hate swordfish and jellyfish ... especially if they are the only means of solving a puzzle!

and in a crowded grid like this - bloody hell!

found two sf in "5" and one in "7", but only because ravel told us they were there.

Guess I'm more a chain guy...

P.S. technically speaking, the "1"s form another swordfish - but that one does not solve anything
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Marty R.



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

PostPosted: Tue Feb 05, 2008 5:31 pm    Post subject: Reply with quote

I've virtually given up looking for swordfish and jellyfish. So much work for so little return. Is there any non-tedious method of spotting them?
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Tue Feb 05, 2008 6:28 pm    Post subject: Reply with quote

that is different that the first move is a swordfish, don't think I have seen that.

because the swordfish is there, this puzzle is rated 4.4 by sudoku explainer.

if you take swordfish out of the solving technique list, the puzzle is rated 7.8

so skipping the swordfish, according to sudoku assistant, you would need two AICs then an extensive chain analysis ( which is basically saying that one of the medusa chains is correct then following it out til you get a contradiction) all before you get one cell solved.

according to SE, you would need 4 forcing chains, then 6 nishio forcing chains before you get a single cell solved, if you skip the swordfish.

good luck,

Norm
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Wed Feb 06, 2008 9:22 am    Post subject: Reply with quote

This diagonal pattern is something special. The average difficulty of random puzzles with this pattern is much higher than usual.

And - it likes swordfish. I cannot really explain why, but when you look at it, you can see, that much possibilities for swordfish are there for each row and column. In other patterns there are much less.
I had looked at the 11 puzzles on one page of the Patterns Game. 6 started with a swordfish as easiest technique, one more had one after a pair.
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Wed Feb 06, 2008 1:31 pm    Post subject: Reply with quote

Marty R. wrote:
I've virtually given up looking for swordfish and jellyfish. So much work for so little return.


Same here. And for the same reason.

Quote:

Is there any non-tedious method of spotting them?


Well, in theory, the same method I use for spotting xwing, kite, coloring chains: draw a grid for each number 1,2,3... with the positions of that number and connect the strong links. In that same grid I look for ERs and (sometimes) swordfish, never for jellyfish. The method is relatively fast, and - since I've drawn the sketches already - not too tedious. But I usually turn to other methods (xy(z)-wing, xy-chains, URs plus the more crooked deadly patterns ravel has started me on - thx ravel Very Happy ) before going over the sketches once more and looking for the stupid swordfish.

One exception: the Times super fiendish. They have said that their puzzles can be solved by x-wing and swordfish so of course I look for them.
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