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hughwill
Joined: 05 Apr 2010
Posts: 424
Location: Birmingham UK
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 Posted: Sun May 15, 2016 9:42 am Post subject: May 15 NVH? |
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After basics (but not all): | Code: |
+----------------+-------------+------------+
| 6 57 578 | 18 4 23 | 15 23 9 |
| 123 9 138 | 5 368 236 | 7 236 4 |
| 235 4 35 | 136 9 7 | 15 236 8 |
+----------------+-------------+------------+
| 137 1367 9 | 2 5 36 | 8 4 16 |
| 145 156 2 | 468 68 9 | 3 7 156 |
| 345 8 356 | 346 7 1 | 2 9 56 |
+----------------+-------------+------------+
| 8 23567 3567 | 9 236 45 | 46 1 37 |
| 137 12367 4 | 367 236 8 | 9 5 37 |
| 9 3567 3567 | 367 1 45 | 46 8 2 |
+----------------+-------------+------------+
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Play this puzzle online at the Daily Sudoku site
A Check on the grade of the above diagram gets "Very Hard' despite
the obvious single 1 in C3. After entering the 1 the grade changes to Easy.
I suspect the bug in the algorithm is around perceiving certain Box-line
reductions as X-Wings (some are very similar). Any other ideas?
Hugh |
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dongrave
Joined: 06 Mar 2014
Posts: 568
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| Posted: Sun May 15, 2016 3:58 pm Post subject: |
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This one's even more surprising than the others! Hey! Wait a minute! No, it's not that surprising. I don't think it quite reached your grid. I think you're right about your Box/Line Reduction theory. I think it's not always correctly prioritizing the locked candidates (in this case, the locked 1's in row 2 of box 1) and is instead applying a Wing on the grid that you posted but with a 1 still in r1c23 and r3c13 (because I don't think it made the last move that you made to eliminate them). I think you're right. I think it's hit or miss when it comes down to a Box/Line Reduction or a Wing.
Update: By the way, I forgot to mention - in this case, the X Wing that it probably applied was the 1's in columns 4 and 7 which removes the exact same candidates as the locked 1's in row 2! |
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hughwill
Joined: 05 Apr 2010
Posts: 424
Location: Birmingham UK
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| Posted: Mon May 16, 2016 11:10 am Post subject: |
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I've always assumed that where there's a box-line reduction any X wing that
does the same job is not really an X-wing because basics take precedence.
However this distinction is arbitrary. On much rarer occasions I've noticed that
puzzles which can be done with basics include XY or XYZ wings though I don't
think the algorithm is ever fooled by these in the same way. |
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dongrave
Joined: 06 Mar 2014
Posts: 568
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| Posted: Mon May 16, 2016 12:11 pm Post subject: |
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| Oh, I think you're definitely right! I should have said 'when it comes down to a Box/Line Reduction or an X-Wing' (not 'or a Wing'). Thanks Hugh! |
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