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Extra Hard 122017

 
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Wed Dec 20, 2017 1:33 pm    Post subject: Extra Hard 122017 Reply with quote

Enjoy the puzzle...Merry Christmas!

Code:

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

Play this puzzle online at the Daily Sudoku site
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Thu Dec 21, 2017 4:13 am    Post subject: Reply with quote

here is after basics

Code:
┌──────────────────────────┬──────────────────────────┬──────────────────────────┐
│  36789      379      689 │   1356   124568     1238 │   1234      146     1346 │
│                          │                          │                          │
│     36        4        2 │      7       16        9 │      5        8      136 │
│                          │                          │                          │
│      5        1       68 │     36     2468      238 │    234        7        9 │
├──────────────────────────┼──────────────────────────┼──────────────────────────┤
│     67       57        1 │      8        3        4 │      9       56        2 │
│                          │                          │                          │
│   4689        2     5689 │    159     1579       17 │     14        3     1468 │
│                          │                          │                          │
│    489       59        3 │      2      159        6 │      7      145      148 │
├──────────────────────────┼──────────────────────────┼──────────────────────────┤
│      2        6        4 │     13      178     1378 │    138        9        5 │
│                          │                          │                          │
│    139        8        7 │      4       19        5 │      6        2       13 │
│                          │                          │                          │
│    139      359       59 │   1369    12689     1238 │   1348       14        7 │
└──────────────────────────┴──────────────────────────┴──────────────────────────┘

XY-Wing (36-1) pivot r3c4=> -1r1c4,r789c5

Here is after the XY-Wing


Code:
+---------------+----------------+---------------+
| 36789 379 689 | 5   12468 1238 | 1234 146 1346 |
| 36    4   2   | 7   16    9    | 5    8   136  |
| 5     1   68  | 36  2468  238  | 234  7   9    |
+---------------+----------------+---------------+
| 67    57  1   | 8   3     4    | 9    56  2    |
| 468   2   568 | 9   157   17   | 14   3   1468 |
| 489   59  3   | 2   15    6    | 7    145 148  |
+---------------+----------------+---------------+
| 2     6   4   | 13  78    378  | 138  9   5    |
| 13    8   7   | 4   9     5    | 6    2   13   |
| 139   359 59  | 136 268   238  | 1348 14  7    |
+---------------+----------------+---------------+


XY-Chain (9=5)r6c2- (5=76)r4c21-(6=319)r289c1=> -9r9c2,r6c1

here is after the XY-Chain

Code:
 +--------------+----------------+---------------+
| 36789 37 689 | 5   12468 1238 | 1234 146 1346 |
| 36    4  2   | 7   16    9    | 5    8   136  |
| 5     1  68  | 36  2468  238  | 234  7   9    |
+--------------+----------------+---------------+
| 67    57 1   | 8   3     4    | 9    56  2    |
| 468   2  568 | 9   157   17   | 14   3   1468 |
| 48    9  3   | 2   15    6    | 7    145 148  |
+--------------+----------------+---------------+
| 2     6  4   | 13  78    378  | 138  9   5    |
| 13    8  7   | 4   9     5    | 6    2   13   |
| 139   35 59  | 136 268   238  | 1348 14  7    |
+--------------+----------------+---------------+

One more wing finishes it.

XY-Wing (36-7) pivot r2c1=> -7r1c1,r4c2
Code:
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Fri Dec 22, 2017 12:32 pm    Post subject: Reply with quote

Very nice Marty.
You are very good (it seems) with chains; I, unfortunately, am not. I get stupefied just trying to follow your path, and end up staring blankly at the puzzle, none the wiser. Consequently, this puzzle took me a bit longer to solve. I used the same initial XY- Wing (36-1), rinsed, found an X-Wing on 3 in r28 c19 which helped marginally, then basically resorted to looking for contradictions via the "if this is true...then that becomes" procedure. It always pays to keep a nice eraser handy...lol.
I eventually solved it, but your approach was by far quicker, and cleaner, as well.
Thanks, Marty, for posting it.
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