## Very nice Very Hard.

Advanced methods and approaches for solving Sudoku puzzles

### Very nice Very Hard.

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.
Karyobin

Posts: 396
Joined: 18 June 2005

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.
scrose

Posts: 322
Joined: 31 May 2005

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

Thomas
rrabbit

Posts: 9
Joined: 22 June 2005

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

Posts: 322
Joined: 31 May 2005

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.
MCC

Posts: 1275
Joined: 08 June 2005

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

Last edited by scrose on Mon Jun 27, 2005 9:42 am, edited 2 times in total.
scrose

Posts: 322
Joined: 31 May 2005

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!
Karyobin

Posts: 396
Joined: 18 June 2005

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.
scrose

Posts: 322
Joined: 31 May 2005

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

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.
MCC

Posts: 1275
Joined: 08 June 2005

Now, you're asking. I'll have to redo the thing and try to find it again. Cheers for that. ;-]
Karyobin

Posts: 396
Joined: 18 June 2005

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.
scrose

Posts: 322
Joined: 31 May 2005

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...
Karyobin

Posts: 396
Joined: 18 June 2005

Ahhhh.... the one that got away!
Last edited by simes on Sun Dec 11, 2011 9:44 am, edited 1 time in total.
simes

Posts: 324
Joined: 11 March 2005
Location: UK

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...
scrose

Posts: 322
Joined: 31 May 2005

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

Posts: 396
Joined: 18 June 2005