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Nov. 26 vh

 
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nataraj



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

PostPosted: Mon Nov 26, 2007 7:01 am    Post subject: Nov. 26 vh Reply with quote

One xy-wing (56-46-45 box 2 and 3) and a UR (45 in boxes 8,9) did it.


first the xy-wing makes r1c7=2, then (r6c7=5, r56c8={2,8} ) r7c8<>2, which leaves the UR:

one of r78c6 must be 6 or 8, together with "68" in r4c6 makes r9c6=5 and the puzzle is solved (I can never remember the UR types, I just know this is one of them)
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andras



Joined: 31 Oct 2007
Posts: 56
Location: Mid Wales

PostPosted: Mon Nov 26, 2007 9:10 am    Post subject: Reply with quote

Actually I don't think you don't need the UR - I found that the xy-wing on its own was enough to break it.

Another very satisfying one, though.

John
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Johan



Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium

PostPosted: Mon Nov 26, 2007 9:36 am    Post subject: Reply with quote

The xy- wing mentioned by nataraj was the final step for me.

Note that the ER in Box 7 for digit <8>, also eliminates <8> in R9C6.
Code:

+--------------------------+--------------------------+-------------------------+
| 246       8         46   | 9          56       7    | 25         3       1    |
| 1         56        7    | 46          3       2    | 8          9       45   |
| 23        235       9    | 48         58       1    | 6          7       245  |
+--------------------------+--------------------------+-------------------------+
|*3468      3         346  | 5          2       *68   | 9          1       7    |
| 7         26        5    | 68         1        9    | 4          28      3    |
| 9         1         28   | 7          4        3    | 25         258     6    |
+--------------------------+--------------------------+-------------------------+
| 568    er 9      er 1    | 3          68       4568 | 7          245     25   |
| 356    er 7      er 36   | 2          9        456  | 1          45      8    |
| 258       4         28   | 1          7        5-[8]| 3          6       9    |
+--------------------------+--------------------------+-------------------------+
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nataraj



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

PostPosted: Mon Nov 26, 2007 9:56 am    Post subject: Reply with quote

andras wrote:
Actually I don't think you don't need the UR - I found that the xy-wing on its own was enough to break it.


That's right. The xy-wing is enough
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Mon Nov 26, 2007 2:13 pm    Post subject: Reply with quote

For the record, following the XY, further down the line I came across:
an X-wing on 6 in Rows 2 and 5 and
a W-wing on 25 in Blocks 1 and 3.

But I gather they were not really necessary.

Peter
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cgordon



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

PostPosted: Mon Nov 26, 2007 2:50 pm    Post subject: Reply with quote

I used an X-wing R25C24 for <6> . Then an ER: R4/Box7 that removes <8> from R7C1.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Mon Nov 26, 2007 10:26 pm    Post subject: Reply with quote

Code:
------------------------------------------------------------------------------|
| 24      8       46      | 9       56%     7       | 2-5     3       1       |
| 1       56      7       | 46%     3       2       | 8       9       45%     |
| 3       25@     9       | 48      58      1       | 6       7@      245@    |
------------------------------------------------------------------------------|
| 48#     3       46      | 5       2       68#     | 9       1       7       |
| 7       26@     5       | 68      1       9       | 4       28@     3@      |
| 9       1       28      | 7       4       3       | 25      58-2    6       |
------------------------------------------------------------------------------|
| 568#    9@      1       | 3       68#     4568#   | 7       245@    25@     |
| 56      7       3       | 2       9       456     | 1       45      8       |
| 258     4       28      | 1       7       5-8     | 3       6       9       |
------------------------------------------------------------------------------|


this is the grid after the x-wing on the 6

the @ is a sword fish on 2 removing 2 from r6c8

the # is a finned x-wing on 8 removing 8 from r9c6

and the % is a xy-wing removing 5 from r1c7

chains !!!! bah humbug
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nataraj



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

PostPosted: Tue Nov 27, 2007 6:54 am    Post subject: Reply with quote

storm_norm wrote:


... x-wing on the 6

... sword fish on 2

... finned x-wing on 8

... xy-wing

chains !!!! bah humbug


Wow. Talk about massive firepower...

"He ran into my knife. He ran into my knife TEN TIMES" (Cell Block Tango)

Somehow I get the feeling you must really hate those poor sudoku Wink Wink
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Tue Nov 27, 2007 6:51 pm    Post subject: Reply with quote

nataraj,

I believe if you go back to the x-wing on the 6's, there is actually a jelly fish on the 6's as well. it does nothing more than the x-wing did. but its interesting to find one.
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cgordon



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

PostPosted: Tue Nov 27, 2007 7:08 pm    Post subject: Reply with quote

Storm Norm: You sure like them Swordfish, Jellyfish and Finned stuff. For me they are like looking for a needle in a haystack. If no other methods existed, I'd chuck it all in. Confused
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nataraj



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

PostPosted: Tue Nov 27, 2007 7:17 pm    Post subject: Reply with quote

this puzzle's got it all ...

amazing.

norm, I can understand your preference for fish'n'fowl, though myself I'm not opposed to more kinky chain based solutions ...

And I realize that the list of possible attacks was more a manifestation of the scientific mind than the actual desire to use them all at the same time.

Couldn't resist to quote that line from "Chicago", though Very Happy

edit: for those of you don't have the dvd ready, here's the scene: http://www.weshow.com/fr/p/9707/catherine_zeta_jones_chante_cell_block_tango
(at time -3:30)


Last edited by nataraj on Tue Nov 27, 2007 7:46 pm; edited 1 time in total
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nataraj



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

PostPosted: Tue Nov 27, 2007 7:35 pm    Post subject: Reply with quote

on a more serious note (and seeing cgordon's post) - the methods I use really depend on what the grid looks like:

when there are still a lot of candidates in many cells, I start looking for xwing, fish etc., basically the search is on a number by number basis. That's when I find even rather long ("multi-coloring") chains.

If (like in this particular case) there are many cells with only two candidates, I try the UR, xy(z)- w- wing and xy-chain approach first

Once I've solved a puzzle I rarely go back to look for alternative ways
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Tue Nov 27, 2007 10:19 pm    Post subject: Reply with quote

anyone who has had an easy sudodu book ( white belt sudoku by michael Rios for example) knows how it feels to kick out puzzle after puzzle. well for me, it was about looking for the 1's, for the 2's, the 3's and so on. x-wing strategy fits into that candidate search and until I researched online, I had no idea what the method was called.

however, coloring can come just as natural.
everyone can remember the first time they saw a sudoku they couldn't solve by scanning alone. oops, what do I do now?

ok, hmm, lets start filling in these candidates and see where I went wrong. OH NO !!! I did nothing wrong. what do I do now?

Cue the locked pair, A.K.A. the Naked Pair.

remember that puzzle?? the one where it looked like two solutions were possible in your budding sudoku career? you were shocked. Naturally, you said "impossible" if I put that number here and that number here, it doesn't work ( imagine that ). your first coloring experiment.

One locked set in a sudoku made you go berserk and now you are on the net looking up sudoku... why didn't I take the BLUE PILL ???!!!
for those of you who like the Matrix.

and down the rabbit hole you went.

welcome to the real world of sudoku. you can't go back to the way you were as an innocent bystander in the sudoku matrix. nope. you are free, free at last from ignorance and condemned all the same for knowing the truth...

once you were in a fantasy world with all the sudoku answers
now you can't skip over any of the biggest questions.
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DennyOR



Joined: 12 Sep 2007
Posts: 33
Location: Portland, Oregon

PostPosted: Tue Nov 27, 2007 11:38 pm    Post subject: Reply with quote

From Johan's position, the 56-64-48-85 XY chain did it for me.
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