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ravel
Joined: 21 Apr 2006
Posts: 536
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 Posted: Wed Jan 23, 2008 6:23 pm Post subject: My hardest DS |
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This is the hardest puzzle in my DS collection.
| Code: | +-------------------+
| . 1 . . . . . . . |
| . . 7 . . . . . . |
| . 2 . 5 . . 6 8 . |
| . . . 8 . 9 . . 2 |
| . 3 . 4 . 7 . . . |
| . . 6 . . . 1 9 . |
| 9 4 . . . . . . 6 |
| . . . . . 2 . . 5 |
| . . . . . . 7 3 . |
+-------------------+
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I dont try to solve such toughies any more. It is about in the class of the one, Asellus has solved in some days. So maybe a Medusa guy wants to invest a lot of time for it ? |
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Wed Jan 23, 2008 7:33 pm Post subject: |
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Actually, I did not want to invest much time.
But I did an experiment all the same and tried Medusa and GEM starting with all bi-value cells just to get a feel for how much the initial selection influences the result. When the method solved one or more cells I stopped and did not go on to look for naked/hidden pairs etc. My question here was rather "does the method solve ANYTHING" than "does it solve the whole puzzle"
Of course, at first I had to reduce the grid, which I did up to here:
| Code: | +--------------------------+--------------------------+--------------------------+
| 568 1 58 | 23679 234789 3468 | 249 2457 3479 |
| 568 9 7 | 236 2348 3468 | 24 1245 134 |
| 34 2 34 | 5 79 1 | 6 8 79 |
+--------------------------+--------------------------+--------------------------+
| 1457 57 145 | 8 6 9 | 3 47 2 |
| 2 3 9 | 4 1 7 | 5 6 8 |
| 478 78 6 | 23 235 35 | 1 9 47 |
+--------------------------+--------------------------+--------------------------+
| 9 4 1358 | 137 3578 358 | 28 12 6 |
| 1378 678 138 | 1369 3489 2 | 489 14 5 |
| 158 568 2 | 169 4589 4568 | 7 3 149 |
+--------------------------+--------------------------+--------------------------+
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I also plotted all single candidates to get a feel for (single) coloring chains. The 7 and 9 plots looked interesting. But, as I said, I tried all bi-values and these are the results depending on the starting cells:
58 (r1c3): nothing
24 (r2c7): nothing
34 (r3c1, r3c3): nothing
79 (r3c5, r3c9): nothing
14 (r4c1): nothing
57 (r4c2): solves r4c2=5
47 (r4c8, r6c9): solves r4c2=5,r4c8=7,r6c9=4
78 (r6c2): finds a "if red [r6c2=7], then..." solution for all cells (green is a dead end). Hm.
23 (r6c4): nothing
35 (r6c6): nothing
28 (r7c7), 12 (r7c8): solves r7c7=8, r7c8=2
14 (r8c8): 4 removed from r1c9, r2c9 but no cells solved
if I count the 78 (r6c2) result as "unsatisfying, but - hm - OK" there are 4 1/2 "good" and 7 "bad" results from the experiment.
If we only look at those starting cells with 7 and/or 9, the results are much better but still far from great:
79 (r3c5, r3c9): nothing
57 (r4c2) solves r4c2=5
47 (r4c8, r6c9): solves r4c2=5,r4c8=7,r6c9=4
78 (r6c2): finds a "if red [r6c2=7], then..." solution for all cells
the best initial bet (has BOTH 7 and 9) yields NOTHING
there are two of the four with cells solved by Medusa/GEM (and probably more with conventional means if you go on)
there is one solution with a "lucky guess" type of starting point
Disclaimer: some or all "nothing" and "unsolved" might well be due to my errors while applying the method
(Edited 2009 GMT for wrong starting grid and resulting wrong statistics and again Thu 1621 GMT to correct a few typos)
Last edited by nataraj on Thu Jan 24, 2008 4:22 pm; edited 2 times in total |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Wed Jan 23, 2008 9:17 pm Post subject: |
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for my two cents and staring long enough to make my eyes hurt, and I have about 3 other people looking at this with me.
those 7,9 bivalue cells are part of a finned x-wing on 9, removes 9 from r8c5
and for the A.P.E. crowd, box 3, I think, contains two. if you do the combinations on the number 4 in column 9, rows 1 and 2, I don't think any combination works. so the 4 in r12c9 can be removed.
good luck with the rest, the snakes of medusa are happy today. |
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Thu Jan 24, 2008 6:51 am Post subject: |
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Now that I've had a good night to sleep on it, I am even more unsatisfied with the outcome of yesterday's Medusa experiment. Noting that practically all the "solved" cells are exactly those that I started out with, there is no big difference to plain forcing in this particular case.
Usually it turns out that Medusa bridges the gaps between the (single) coloring chains and there are either useful exclusions to make or else a color wrap that solves a bunch of cells in one step. Not this time.
Truly a mean bugger, this puzzle. |
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