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Free Press April 22, 2011

 
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Fri Apr 22, 2011 2:25 pm    Post subject: Free Press April 22, 2011 Reply with quote
Not yet started. Seems to be on the hard side.
Code:
Puzzle: FP042211
+-------+-------+-------+
| 8 7 . | 1 . . | . . . |
| . . 2 | . . . | 1 . 4 |
| . . . | . 5 9 | 7 8 . |
+-------+-------+-------+
| 3 . . | 4 . 6 | . . . |
| . . 7 | . . . | 9 . . |
| . . . | 8 . 3 | . . 6 |
+-------+-------+-------+
| . 4 5 | 9 . . | . . . |
| 2 . 3 | . . . | 4 . . |
| . . . | . . 7 | . 5 9 |
+-------+-------+-------+

Play this puzzle online at the Daily Sudoku site

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Fri Apr 22, 2011 11:12 pm    Post subject: Reply with quote
Quote:
Seems to be on the hard side.

You'll get no argument from me. All I could find was a worthless W-Wing (or Skyscraper) that eliminated a couple of 2s. After that, Medusa traps and a wrap set up a puzzle-ending Multi-coloring; r7c5<>6.

Medusa's fun to watch develop while doing it, but I consider it largely trial-and-error, so I'm not very satisfied when I have to resort to it.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Apr 23, 2011 12:48 am    Post subject: Reply with quote
Marty,

I have not solved it, but noticed a couple of bizarre moves. After basics (Grid A):
Code:
+-------------------+-------------------+-------------------+
| 8     7     69d   | 1     236   4     |-2356  2369  235   |
| 59    35-6  2     | 7     36    8     | 1    -369e  4     |
| 146   13-6  146c  | 236@  5     9     | 7     8     23g   |
+-------------------+-------------------+-------------------+
| 3     1258  189   | 4     79    6     | 258   127   12578 |
| 46    68a   7     | 25    12    125   | 9     34    38    |
| 59    125   149   | 8     79    3     | 25    1247  6     |
+-------------------+-------------------+-------------------+
| 7     4     5     | 9   -1-2368 12    | 2368  1236 1-238  |
| 2     9     3     | 56    168   15    | 4     167   178   |
| 16    168   168b  | 23@   4     7     | 23f   5     9     |
+-------------------+-------------------+-------------------+

Some kind of M-wing: If a is 8, b is 8. If b is not 6, one of cd is 6. Eliminating 6 in R23C2. Shocked

If d is 6, e is 6. If d is 9, e is 9. Eliminating 3 in e. Shocked

f and g are a W-wing, taking out 2 as shown in C79.

There is a type 6 UR 12 taking out 12 in R7C5. Cool

Leaving us here (Grid B):
Code:
+-------------------+-------------------+-------------------+
| 8     7     69    | 1     236   4     | 356   2369  235   |
| 59    35    2     | 7     36    8     | 1     69    4     |
| 146   13    146   | 236   5     9     | 7     8     23    |
+-------------------+-------------------+-------------------+
| 3     1258  189   | 4     79    6     | 258   127   12578 |
| 46    68    7     | 25    12    125   | 9     34    38    |
| 59    125   149   | 8     79    3     | 25    1247  6     |
+-------------------+-------------------+-------------------+
| 7     4     5     | 9     368   12    | 2368  1236  138   |
| 2     9     3     | 56    168   15    | 4     167   178   |
| 16    168   168   | 23    4     7     | 23    5     9     |
+-------------------+-------------------+-------------------+


More to come, if I make progress.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Apr 23, 2011 3:42 am    Post subject: Reply with quote
Keith, those first two moves are very impressive. In the remaining grid I see an M-Wing and Kite offhand, but don't know how far they take you.
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peterj



Joined: 26 Mar 2010
Posts: 974
Location: London, UK
PostPosted: Sat Apr 23, 2011 7:33 am    Post subject: Reply with quote
A UR move takes it down...
Code:
ur(25)r46c27[(8)r4c7=(5)r6c1] - (5=9)r2c1 - (9=6)r1c3 - r1c7=r7c7 ; r7c7<>8

(Using an internal and external strong inference)
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Apr 23, 2011 1:10 pm    Post subject: Reply with quote
peterj wrote:
A UR move takes it down...
Code:
ur(25)r46c27[(8)r4c7=(5)r6c1] - (5=9)r2c1 - (9=6)r1c3 - r1c7=r7c7 ; r7c7<>8

(Using an internal and external strong inference)

I don't see this. Can someone spell it out?

Keith
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peterj



Joined: 26 Mar 2010
Posts: 974
Location: London, UK
PostPosted: Sat Apr 23, 2011 1:52 pm    Post subject: Reply with quote
keith wrote:
I don't see this. Can someone spell it out?

To stop the potential DP(25) in r46c28 at least one of...

(1) r4c7=8 (external strong inference)
(2) r6c1=5 (internal strong inference)

For (2) consider that (25) is almost a hidden pair in block 4 i.e. the only thing stopping it becoming a naked (25) and so part of the DP is the (5)r6c1. (You can get the same result by considering the external DP-stoppers (18)r4c2 and (1)r6c2 - it's just more painful!)

Now, if (5)r6c1 then (9)r2c1 and (6)r1c3 => r1c7<>6 and r7c7 must be 6.
So in both case (1) and (2), r7c7<>8
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Apr 23, 2011 2:03 pm    Post subject: Reply with quote
Thanks.

Keith
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Sat Apr 23, 2011 4:33 pm    Post subject: Reply with quote
An alternative suggestion for the first strong inference:

Code:
(8)r4c7 = UR_4[(25)r46c7 - (5)r46c2] = (5)r6c1

This way, the UR includes a necessary weak inference!

[Edit: decided to move the initial assumption outside the UR_4.]

Last edited by daj95376 on Sat Apr 23, 2011 8:33 pm; edited 2 times in total
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Sat Apr 23, 2011 4:54 pm    Post subject: Reply with quote
My solver missed the UR_4 option and found an awkward network, instead. I turned it into Sad :

Code:
 Kraken Cell [r7c9]

 (1)r7c9 - (1=2)r7c6   - r9c4 = r9c7 - (25=8)r64c7 - (8)r7c7
     ||
 (2)r7c9 - r3c9 = r3c4 - r9c4 = r9c7 - (25=8)r64c7 - (8)r7c7
     ||
 (3)r7c9 -                 (3=2)r9c7 - (25=8)r64c7 - (8)r7c7
     ||
 (8)r7c9                                           - (8)r7c7
 +-----------------------------------------------------------------------+
 |  8      7      69     |  1      236    4      |  2356   2369   235    |
 |  59     356    2      |  7      36     8      |  1      369    4      |
 |  146    136    146    |  236    5      9      |  7      8      23     |
 |-----------------------+-----------------------+-----------------------|
 |  3      1258   189    |  4      79     6      |  258    127    12578  |
 |  46     68     7      |  25     12     125    |  9      34     38     |
 |  59     125    149    |  8      79     3      |  25     1247   6      |
 |-----------------------+-----------------------+-----------------------|
 |  7      4      5      |  9      12368  12     |  2368   1236   1238   |
 |  2      9      3      |  56     168    15     |  4      167    178    |
 |  16     168    168    |  23     4      7      |  23     5      9      |
 +-----------------------------------------------------------------------+
 # 87 eliminations remain
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Apr 23, 2011 5:41 pm    Post subject: Reply with quote
The first three blocks from my grid B:
Code:
+-------------------+-------------------+-------------------+
| 8     7     69    | 1     23-6k 4     | 356   2369  235   |
| 59    35    2     | 7     36    8     | 1     69    4     |
| 146   13    146   | 236   5     9     | 7     8     23j   |
+-------------------+-------------------+-------------------+
We can eliminate 6 from k, since j and k must be the same value.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sun Apr 24, 2011 12:12 am    Post subject: Reply with quote
keith wrote:
The first three blocks from my grid B:
Code:
+-------------------+-------------------+-------------------+
| 8     7     69    | 1     23-6k 4     | 356   2369  235   |
| 59    35    2     | 7     36    8     | 1     69    4     |
| 146   13    146   | 236   5     9     | 7     8     23j   |
+-------------------+-------------------+-------------------+
We can eliminate 6 from k, since j and k must be the same value.

Keith

Dare I ask what says j and k must be the same value?
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sun Apr 24, 2011 12:33 am    Post subject: Reply with quote
Marty,

I'll put something in the Solving Techniques Forum.

http://www.dailysudoku.com/sudoku/forums/viewtopic.php?p=30184#30184

Keith
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ronk



Joined: 07 May 2006
Posts: 398
PostPosted: Sun Apr 24, 2011 1:28 am    Post subject: Reply with quote
Marty R. wrote:
keith wrote:
The first three blocks from my grid B:
Code:
+-------------------+-------------------+-------------------+
| 8     7     69    | 1     23-6k 4     | 356   2369  235   |
| 59    35    2     | 7     36    8     | 1     69    4     |
| 146   13    146   | 236   5     9     | 7     8     23j   |
+-------------------+-------------------+-------------------+
We can eliminate 6 from k, since j and k must be the same value.

Dare I ask what says j and k must be the same value?

It is due to one of several possible m-rings.

_______
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Sun Apr 24, 2011 1:50 am    Post subject: Reply with quote
Marty R. wrote:
keith wrote:
The first three blocks from my grid B:
Code:
+-------------------+-------------------+-------------------+
| 8     7     69    | 1     23-6k 4     | 356   2369  235   |
| 59    35    2     | 7     36    8     | 1     69    4     |
| 146   13    146   | 236   5     9     | 7     8     23j   |
+-------------------+-------------------+-------------------+
We can eliminate 6 from k, since j and k must be the same value.

Keith

Dare I ask what says j and k must be the same value?

S-Loop/Ring:

Code:
(2)r1c5 = r1c89 - (2=3)r3c9 - r1c789 = (3)r1c5 - loop  =>  r1c5<>6
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