Very nice Very Hard.

Advanced methods and approaches for solving Sudoku puzzles

Very nice Very Hard.

Postby Karyobin » Wed Jun 22, 2005 7:13 pm

Here's one for you to ponder...

* 6 * 9 * * * * 8
* * 3 * * 5 * * *
8 7 * * * * 3 9 *
* * * * 5 7 * 4 *
* * 6 * * * 7 * *
* 1 * 8 2 * * * *
* 4 1 * * * * 3 2
* * * 1 * * 4 * *
3 * * * * 2 * 7 *

Cracked it myself but I had to find a four-pair swordfish. Did I (as usual) look too hard? Are there easier approaches? Would be interested to how anyone else out there finds it.
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Postby scrose » Wed Jun 22, 2005 8:14 pm

Yes, I think there is an easier way. You can make quite a few eliminations based on pairs. Eventually these eliminations will reveal an x-wing which lets you make more eliminations. The puzzle is wide open from there on.

However, the easier way is not necessarily the better way.
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Postby rrabbit » Wed Jun 22, 2005 8:28 pm

You don't need swordfishs or x-wings. Begin by looking where
the 7s can be.


Thomas
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Postby scrose » Wed Jun 22, 2005 8:45 pm

rrabbit wrote:You don't need swordfishs or x-wings. Begin by looking where the 7s can be.

I believe you are incorrect. Yes, the 7's get you off to a quick start, but they do not prevent an x-wing from being required. Based on the given clues, exactly 19 additional cells can be filled before having to use the x-wing technique.

If you wish to, you can send me your cell-by-cell solution as a private message, and I can try to explain where the mistake is.
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Postby MCC » Sun Jun 26, 2005 2:14 pm

scrose wrote:
rrabbit wrote:You don't need swordfishs or x-wings. Begin by looking where the 7s can be.

I believe you are incorrect. Yes, the 7's get you off to a quick start, but they do not prevent an x-wing from being required. Based on the given clues, exactly 19 additional cells can be filled before having to use the x-wing technique.

If you wish to, you can send me your cell-by-cell solution as a private message, and I can try to explain where the mistake is.


scrose are you sure about needing an x-wing, I got to this position without using x-wings.


*6* 973 **8
**3 485 **7
875 2** 394
----------------
*3* 657 *41
**6 3** 7**
71* 82* **3
----------------
*41 7** *32
**7 13* 4**
3** 542 176

Then looking at row 6, columns 7,8 the pair 5 and 6 can only go in these positions, from there the puzzle is easily finished.

I'm sure you'll let me know otherwise.
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Postby scrose » Sun Jun 26, 2005 5:12 pm

MCC, the grid you have showing cannot be solved. How were you able to place the 7's in r6c1 and r8c3?

Updated: Added clairification.
Last edited by scrose on Mon Jun 27, 2005 9:42 am, edited 2 times in total.
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Postby Karyobin » Mon Jun 27, 2005 12:11 pm

Well anyway. Can't say I didn't honestly expect there to be a much easier way than my spectacular 4-way swordfish, but I just love looking for 'em!
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Postby scrose » Mon Jun 27, 2005 1:29 pm

Karyobin wrote:...my spectacular 4-way swordfish...

I believe a 4-way swordfish is called a jellyfish. Since I've never encountered a jellyfish in sudoku (or in the ocean, for that matter), I am curious to know which digit you used to form it? Just a hint, please; I would like to try and find it on my own.
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Postby MCC » Mon Jun 27, 2005 2:27 pm

scrose wrote:MCC, the grid you have showing cannot be solved. How were you able to place the 7's in r6c1 and r8c3?

Updated: Added clairification.


scrose, my apologies, you were right, I can only blame the heat and humidity for turning by brain to mush. Ignore previous grid.

Having redone the puzzle I realised I had too few pencilmarks when I first did the puzzle and had made a total hash of it.

As you said, 19 additions then an x-wing in the 5's.
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Postby Karyobin » Mon Jun 27, 2005 4:09 pm

Now, you're asking. I'll have to redo the thing and try to find it again. Cheers for that. ;-]
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Postby scrose » Mon Jun 27, 2005 4:47 pm

Karyobin wrote:Now, you're asking. I'll have to redo the thing and try to find it again.

:)No worries! Don't go through the trouble if you can't remember off of the top of your head which digit it was. I'll try and find it myself.
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Postby Karyobin » Mon Jun 27, 2005 6:02 pm

Did it again anyway. Swordfish didn't turn up this time. I think it was probably caused by my incorrectly crossing out a few candidates. You should have seen it though, the way it shimmered, beautiful...
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Postby simes » Mon Jun 27, 2005 6:11 pm

Ahhhh.... the one that got away!
Last edited by simes on Sun Dec 11, 2011 9:44 am, edited 1 time in total.
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Postby scrose » Mon Jun 27, 2005 6:13 pm

Karyobin wrote:You should have seen it though, the way it shimmered, beautiful...
simes wrote: Ahhhh.... the one that got away!

That elusive white whale! Or rather, a purple jellyfish...
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Postby Karyobin » Tue Jun 28, 2005 3:07 pm

Simes - did you name your server after the lorry driver in Pigeon Street? Remember - Long Distance Clara?
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