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Extreme 082720

 
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Thu Aug 27, 2020 8:52 pm    Post subject: Extreme 082720 Reply with quote

One for the chain gang...

Code:

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

Play this puzzle online at the Daily Sudoku site

cheers...immp
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dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Fri Aug 28, 2020 12:03 pm    Post subject: Reply with quote

Code:
+-----------------+------------+----------------+
| 4679 278  24679 | 468 5   3  | 1    2689 89   |
| 3469 1    469   | 2   478 78 | 5    3689 389  |
| 356  2358 26    | 68  1   9  | 236  4    7    |
+-----------------+------------+----------------+
| 567  9    167   | 35  67  4  | 8    13   2    |
| 2    57   167   | 35  678 78 | 39   139  4    |
| 8    4    3     | 9   2   1  | 7    5    6    |
+-----------------+------------+----------------+
| 1    6    249   | 7   49  25 | 2349 2389 3589 |
| 349  23   5     | 48  489 6  | 249  7    1    |
| 479  27   8     | 1   3   25 | 2469 269  59   |
+-----------------+------------+----------------+

This is probably the ugliest one step solution that you'll ever see but I think the logic is right. I used the symbols '*', '@', and '$' to mark cell values referenced later on in the chain. (I learned that trick recently from Clement.) The '$' is probably not needed here though because it references a cell value in the same column from just 2 steps earlier.

6r3c4-(6=2*)r3c3-(26=3@)r3c7-(3=2|4|9)r7c357-(2=5)r7c6-(5=2)r9c6-(2=7$)r9c2-(7=5)r5c2-(2*3@5=8)r3c2-(7$8=2)r1c2; contradiction (i.e. 2r3c3 and 2r1c2) => r3c4 <> 6; stte.
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Fri Aug 28, 2020 6:32 pm    Post subject: Reply with quote

Hello Don. Now, mind you, I hate chains...despise them in fact, but I know that in some of these really tough puzzles I may have to resort to using them. So I am at least familiar with them. You may make the logic notation as ugly as you like because I say "Hats off" to you for doing it in one step! I sure am not capable of that. It took me several steps, using several wing variations, and THEN several (I recall using three) XY-Chains to solve.

cheers...immp
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Clement



Joined: 24 Apr 2006
Posts: 1110
Location: Dar es Salaam Tanzania

PostPosted: Sat Aug 29, 2020 7:55 pm    Post subject: Extreme 082720 Reply with quote

Code:

+----------------------+-----------------+---------------------+
| 4679   h278    24679 |  468   5     3  | 1      c2689   89   |
| 3469    1      469   |  2     478   78 | 5      c3689   389  |
| 356    i2358  b26    |ja8-6   1     9  |b236     4      7    |
+----------------------+-----------------+---------------------+
| 567     9      167   |  35    67    4  | 8       13     2    |
| 2       57     167   |  35    678   78 | 39      139    4    |
| 8       4      3     |  9     2     1  | 7       5      6    |
+----------------------+-----------------+---------------------+
| 1       6      249   |  7     489   25 | 2349    2389   3589 |
| 349     23     5     |  48    489   6  | 249     7      1    |
|f479    g27     8     |  1     3     25 |e2469   d269    59   |
+----------------------+-----------------+---------------------+

Oho! Same starting point and same elimination as Dongrave, may be a different route
6r3c4 - [(6=2*)r3c3 -(6)r3c7)] = r13c8 - r9c8 = (6-4)r9c7 = (4-7)r9c1 = r9c2 - (72*=8)r1c2 - r3c2 = (8)r3c4 => - 6r3c4; btte
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