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WebSudoku 'Evil' Puzzle

 
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PeteGrant



Joined: 17 Feb 2006
Posts: 10
Location: Saranac Lake, New York

PostPosted: Sun May 07, 2006 12:27 pm    Post subject: WebSudoku 'Evil' Puzzle Reply with quote

Ran into a dead-end with an "Evil" puzzle from WebSudoku.com. Here's what I have so far:

Code:

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


The Draw facility show that I should place a 9 in r4c6 but I fail to see the pattern that dictates this. Here's what I have as possibilities:

Code:

+------------------------------------------------------------------+
|  1238     38     5  |      6      7   128  |    23     9     4   |
|     9    678     4  |      3      5   128  |    26   267 12678   |
|  1236     36     7  |      9      4    12  |     5     8  1236   |
+------------------------------------------------------------------+
|    68      5     2  |      7      3    69  |     4     1    689  |
| 13678  36789 13689  |      4     12    69  | 23689     5  23689  |
|   136      4  1369  |      8     12     5  |     7   236   2369  |
+------------------------------------------------------------------+
|   367      2   369  |      5      8     4  |     1   367   3679  |
|     4   6789   689  |      1     69     3  |  2689   267      5  |
|     5      1  3689  |      2     69     7  |  3689     4   3689  |
+------------------------------------------------------------------+


What am I missing?

TIA,
Pete
________
Janesville Assembly


Last edited by PeteGrant on Thu Feb 03, 2011 10:05 am; edited 1 time in total
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Sun May 07, 2006 1:00 pm    Post subject: Reply with quote

There is a box/line or box/box interaction (number 1), which leads to a hidden pair.
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PeteGrant



Joined: 17 Feb 2006
Posts: 10
Location: Saranac Lake, New York

PostPosted: Sun May 07, 2006 1:34 pm    Post subject: Reply with quote

Thank you, ravel, for responding, but I don't see the hidden pair -- yet. Could you point out the cells that constitute the interaction?

Thanks
Pete
________
vapormatic vaporizer


Last edited by PeteGrant on Thu Feb 03, 2011 10:05 am; edited 1 time in total
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Angel



Joined: 26 Mar 2006
Posts: 31

PostPosted: Sun May 07, 2006 2:26 pm    Post subject: Reply with quote

From the postion you posted, I would note that since 7 is already placed in box 1 you can eliminate it from the possibilities for r2c2. This then leads to a triple {3,6,8} in r1c2, r2c2, r3c2. Therefore there is a pair {1,2} in r1c1, r3c1. Also there is then a pair {1,2} in r3c1, r3c6, which reduces the possibilities for r3c9. Then looking at box 3 you will have another triple (and check the 8 which is already placed but still appears as a candidate).

Over to you after that.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Sun May 07, 2006 6:52 pm    Post subject: Reply with quote

PeteGrant wrote:
Thank you, ravel, for responding, but I don't see the hidden pair -- yet. Could you point out the cells that constitute the interaction?

The way, Angel did it - spotting the triple, which gives the pair, is a bit easier, but i did not see the triple because of the 7.

The 1 in box 1 can only be in column 1 (therefore must be there), so it cannot be in the rest of the column (box/line interaction) and it can be eliminated from r5c1 and r6c1. This leaves the hidden pair 12 in r13c1.
Sorry, there is no box/box elimination for the same.

PS: I dont really understand the hint r4c6=9. i would need the following chain to get that:
r4c6=6 => r5c6=9 => r6c3=9 => r7c9=9 => r4c6=9
which is very complicated compared to a naked triple.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sun May 07, 2006 11:08 pm    Post subject: Reply with quote

There is a swordfish on 9's that excludes 9 from r5c6, leaving r4c6 as the only place for a 9 in box 5 but it also leaves r5c6 as a naked single, which seems a more appropriate hint.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Mon May 08, 2006 7:34 am    Post subject: Reply with quote

Well spotted Smile
Looking for the swordfish i first saw the x-wing in rows 6 and 7, that kills the 9 in r4c9 => r4c6=9.
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PeteGrant



Joined: 17 Feb 2006
Posts: 10
Location: Saranac Lake, New York

PostPosted: Mon May 08, 2006 10:40 am    Post subject: Reply with quote

Thank you all for your input. This was one of those cases where the more I looked, the more I missed Smile

BTW, WebSudoku's "evil" puzzles seem to be of about the same difficulty as DailySudoku's "hard". I haven't dared to try the "very hard" yet....
________
3/15
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