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Set E Puzzle 4

 
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Tue Dec 02, 2008 9:49 pm    Post subject: Set E Puzzle 4 Reply with quote

Since my alerts seem to be extraneous. I won't suggest a Swordfish or chain for this puzzle.

Code:
 +-----------------------+
 | . . . | . . . | 7 2 . |
 | . . . | . . 8 | 1 . . |
 | . . . | 2 3 . | . . . |
 |-------+-------+-------|
 | . . 2 | . . 7 | 9 . . |
 | . . 3 | . 9 6 | 4 . . |
 | . 7 . | 8 4 . | . . 6 |
 |-------+-------+-------|
 | 5 8 . | 7 6 . | . 9 3 |
 | 6 . . | . . . | 8 4 . |
 | . . . | . . 3 | 6 . 7 |
 +-----------------------+

Play this puzzle online at the Daily Sudoku site
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Wed Dec 03, 2008 3:41 am    Post subject: Reply with quote

another alert for this puzzle is "classic remote naked pair" as there are two of them from the get go.
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Marty R.



Joined: 12 Feb 2006
Posts: 5166
Location: Rochester, NY, USA

PostPosted: Wed Dec 03, 2008 4:49 am    Post subject: Reply with quote

I might have to try this again. I had 11 moves involving W-Wings, Remote Pairs, coloring, Hidden URs and X-Wings before grinding to a halt and getting out my Medusa crutch.
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Dec 03, 2008 5:47 am    Post subject: Re: Set E Puzzle 4 Reply with quote

daj95376 wrote:
Since my alerts seem to be extraneous. I won't suggest a Swordfish or chain for this puzzle.

Let me rephrase the above.

Since my alerts seem so often not to be needed, I'm not going to issue an alert for techniques that I used in this puzzle. Exclamation
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Wed Dec 03, 2008 8:30 am    Post subject: Reply with quote

Code:
.------------------------.------------------------.------------------------.
| 3    -(15)49    145689 | 14569  #15      1459   | 7       2       489    |
|*29     *2459    4569   | 4569    7       8      | 1       3       49     |
| 7       149     1489   | 2       3       149    | 5       6       489    |
:------------------------+------------------------+------------------------:
| 4       6       2      | 3      #15%     7      | 9       8      %15     |
| 8      #15      3      |#15%     9       6      | 4       7       2      |
| 19      7       159    | 8       4       2      | 3       15      6      |
:------------------------+------------------------+------------------------:
| 5       8       14     | 7       6       14     | 2       9       3      |
| 6       3       7      |-(15)9   2       159    | 8       4      %15     |
|*129   *124-9    149    |415      8       3      | 6       15      7      |
'------------------------'------------------------'------------------------'


visually, the two tangent classic remote pairs are present on {1,5} means {1,5} is gone from r8c4 and r1c2.
as well as the type 5 UR (I think) on{2,9} r29c12 with two strong links on 2, which means 9 is gone from r9c2.

Code:
.------------------.------------------.------------------.
| 3     49    1568 | 1456  15    1459 | 7     2     489  |
| 2     459   56   | 456   7     8    | 1     3     49   |
| 7     149   18   | 2     3     149  | 5     6     489  |
:------------------+------------------+------------------:
| 4     6     2    | 3     15    7    | 9     8     15   |
| 8     15    3    | 15    9     6    | 4     7     2    |
| 19    7     159  | 8     4     2    | 3     15    6    |
:------------------+------------------+------------------:
| 5     8     14   | 7     6     14   | 2     9     3    |
| 6     3     7    | 9     2     15   | 8     4     15   |
| 19    2     149  | 145   8     3    | 6     15    7    |
'------------------'------------------'------------------'

the UR {1,9} r69c13 makes two of the same eliminations as the x-wing on 1... r69c3 and r9c4 is not 1.
the type 5 UR on {5,6} r12c34 removes 5 from r1c4
and still have the swordfish on 5 which removes the 5 in r1c3
leaves this xy-chain- (4=9)r9c3 - (9=5)r6c3 - (5=6)r2c3 - (6=4)r2c4; r9c4 <>4... to finish it.
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Dec 03, 2008 10:09 am    Post subject: Reply with quote

storm_norm wrote:
visually, the two tangent classic remote pairs are present on {1,5} means {1,5} is gone from r8c4 and r1c2.

Fold in [c8] and you have a third remote pair that eliminates {1} from r9c2.
(Yeah, I know, it doesn't help much.)

Whew!!! Not your boring ole' XY-Wing single-stepper, huh?
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Marty R.



Joined: 12 Feb 2006
Posts: 5166
Location: Rochester, NY, USA

PostPosted: Wed Dec 03, 2008 4:58 pm    Post subject: Reply with quote

Quote:
as well as the type 5 UR (I think) on{2,9} r29c12 with two strong links on 2, which means 9 is gone from r9c2.

That's not a Type 5, at least based on Keith's UR treatise, but it is a type of Hidden UR as described by Sudopedia (and perhaps others).

http://www.sudopedia.org/wiki/Uniqueness_Test

Quote:
Since my alerts seem so often not to be needed, I'm not going to issue an alert for techniques that I used in this puzzle.


Without going to a lot of trouble, is there a way you could provide a degree of difficulty?
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Dec 03, 2008 7:40 pm    Post subject: Reply with quote

Marty R. wrote:
Without going to a lot of trouble, is there a way you could provide a degree of difficulty?

I posted several puzzles that I thought would take several steps to solve. Others found them to be single/double-steppers. Sad

Many of the puzzles in Set E aren't going to be solved so easily because they were generated with XY-Chains being allowed (but not necessarily required).

This one qualifies as extreme because of the Swordfish, XY-Chains, and complex URs present.

Fortunately, there are some puzzles in Set E that only qualify as darn ugly. Very Happy
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cgordon



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

PostPosted: Wed Dec 03, 2008 7:48 pm    Post subject: Reply with quote

Very straightforward at first!

Two ER's on <1>
an x wing on <1>
an ER on<5>
a bit of colouring on <5>
an xyz wing
then (and this was brilliant) a Sue de Coq from Box 1 C2

...... but then I get stuck.

I'm left with a whole bunch of <15>s but they don't form any Classic Remote Pair - at least not for me - the chains are all odd numbered
And I sure don't see ant Type UR for <29>. How can you have a UR with only one pair.

This was a cruel one!
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Wed Dec 03, 2008 8:18 pm    Post subject: Reply with quote

Quote:
That's not a Type 5, at least based on Keith's UR treatise, but it is a type of Hidden UR as described by Sudopedia (and perhaps others).


yep, you are right, its not a type 5, its a hidden one. at least the eliminations are correct Cool

oh by the way, this rated in at a 7.2 SE
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Dec 03, 2008 8:27 pm    Post subject: Reply with quote

cgordon wrote:
This was a cruel one!

Yes, in retrospect, I shouldn't have posted this puzzle. My apologies Exclamation

After basics, X-Wing, Swordfish, and Colors, I single-stepped several XY-Chains by using a Remote Pair chain, alternately colored Blue and Green, to force a UR contradiction.

Code:
 Remote Pair: (5=1)r5c2 - (1=5)r5c4 = (5-1)r4c5 - (1=5)r1c5

 ( [r5c2]=1 => [r1c5]=5 ) => (49) UR [r13c26] ==>> [r5c2]<>1

 reduces puzzle to Naked Singles
 +--------------------------------------------------------------+
 |  3     49    4689  |  146  G15    49+5  |  7     2     489   |
 |  29    2459  4569  |  46    7     8     |  1     3     49    |
 |  7     49+1  1489  |  2     3     49    |  5     6     489   |
 |--------------------+--------------------+--------------------|
 |  4     6     2     |  3    B15    7     |  9     8     15    |
 |  8    B15    3     | G15    9     6     |  4     7     2     |
 |  19    7     59    |  8     4     2     |  3     15    6     |
 |--------------------+--------------------+--------------------|
 |  5     8     14    |  7     6     14    |  2     9     3     |
 |  6     3     7     |  9     2     15    |  8     4     15    |
 |  129   249   49    |  45    8     3     |  6     15    7     |
 +--------------------------------------------------------------+

Another way to view the UR is [r3c2]=1 and/or [r1c6]=5. No matter what combination is true, all of the Blue cells are forced to {5} and all of the Green cells are forced to {1}. Not as elegant as my description!
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cgordon



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

PostPosted: Wed Dec 03, 2008 8:57 pm    Post subject: Reply with quote

Actually I forgot to mention I also had a Type 6 UR (49) which knocked off the <9> in R3C2.

What's a 7.2 rating. Is that like a Class 7 Hurricane or 7.2 on the Richter Scale - i.e something that is life-threatening?
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Thu Dec 04, 2008 11:28 pm    Post subject: Reply with quote

Quote:
And I sure don't see any Type UR for <29>. How can you have a UR with only one pair.


Consider this case:
Code:
29   29x

29y  29z
where the corners are also an X-wing on <2>. x, y, z are any candidates. <9> in the bottom right cell forces <2> in the upper right and lower left, which forces <9> in the upper left; a DP. So, the lower right cannot be <9>.

If you have
Code:
29   29x

29y  29
you can immediately simplify it to
Code:
2   9x

9y  2
These have been called both "Type 6" and "Hidden" UR's.

In the end, these seem not to be very useful, although Mike Barker used them to crack a few previously "unsolvable" puzzles. The way I see it is this: The UR argument is maybe going to solve the X-wing candidates on one diagonal or the other. Since you have already made the X-wing eliminations (which have nothing to do with the UR), the effect on the rest of the puzzle is small.

That is the case in the puzzle of this thread: Solving the remaining <2>'s does not help much.

Keith
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cgordon



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

PostPosted: Fri Dec 05, 2008 5:24 pm    Post subject: Reply with quote

Quote:

29 29x

29y 29z
where the corners are also an X-wing on <2>. x, y, z are any candidates. <9> in the bottom right cell forces <2> in the upper right and lower left, which forces <9> in the upper left; a DP. So, the lower right cannot be <9>.

Keith:
I'm lost here. I understand Type 6 UR's in that if there was a strong link on <2> in the top row and the bottom right cell was a 29 (not a 29z) - you can remove the <2> from the 29y. (like a diagonal variant of a Type 4). Was this incorrect?
I also don't understand in your example why you can assume the bottom left is a <9> and not a <z>.
Confused.
Cheers,
Craig
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