Hi yzfwsf,
Tough puzzle on sudoku.com.au site, September 28, 2020
..83..41.7.............7.8..72..3...5...9...1...4..62..6.8.............6.23..95..
My solution:
- Code: Select all
+--------------------------+-------------------------+------------------------+
| 269 59 8 | 3 256 26 | 4 1 7 |
| 7 1345 145 | 1259 12458 1248 | 239 6 2359 |
| 12346 1345 1456 | 12569 12456 7 | 239 8 2359 |
+--------------------------+-------------------------+------------------------+
| 4689 7 2 | 16 168 3 | 89 5 489 |
| 5 348 46 | 26 9 268 | 378 347 1 |
| 1389 1389 19 | 4 7 5 | 6 2 389 |
+--------------------------+-------------------------+------------------------+
| 149 6 14579 | 8 12345 124 | 1237 3479 234 |
| 1489 14589 14579 | 1257 12345 124 | 12378 3479 6 |
| 148 2 3 | 167 146 9 | 5 47 48 |
+--------------------------+-------------------------+------------------------+
1. (9=186)r4c457 - a6 = (62-3)r13c1 = r6c1 - (3=489)r469c9 loop =>-9a1, -14a7, -3b4, -4i3, -8r4c19; singles to 81
Your solver proposes:
- tough28092020.png (31.02 KiB) Viewed 158 times
Almost Locked Set XY-Wing ,Triple Links: A=r4c457{1689}, B=r469c9{3489}, C=r46789c1{134689}, X,Y=6, 3, Z=9 => r6c2<>3 r7c9<>4 r3c1<>1 r3c1<>4 r1c1<>9
that could be written as the loop
(9=186)r4c457 - (6=14893)r46789c1 - (3=489)r469c9 loop => -3r6c2, -4 r7c9, -14r3c1, -9r1c1 (equivalent to mine, with ALS r46789c1 vs AHS r13c1)
This loop eliminates -8r4c19 also (from application of the process to the weak links internal to each ALS, here the WL 8r4c5 - 8r4c7) Does your solver misses it, or do you discard the cannibalistic eliminations for any reason ?
Hereafter, the pigeonhole matrix (PM) of the move. It is a symmetrical matrix, therefore any candidate in sight of one column is eliminated.
- Code: Select all
1r9c1 4r9c1 8r9c1
1r8c1 4r8c1 8r8c1 9r8c1
1r7c1 4r7c1 9r7c1
1r6c1 8r6c1 9r6c1 3r6c1
4r4c1 8r4c1 9r4c1 6r4c1
6r4c4 1r4c4
6r4c5 1r4c5 8r4c5
8r4c6 9r4c6
9r4c9 4r4c9 8r4c9
3r6c9 9r6c9 8r6c9
4r9c9 8r9c9
-----------------------------------------------------------------
-1r3c1 -4r3c1 -9r1c1 -3r6c2 -8r4c19 -4r7c9