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Sudoku San - Ferocious 18-Aug-2005

 
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alanr555



Joined: 01 Aug 2005
Posts: 194
Location: Bideford Devon EX39

PostPosted: Thu Sep 22, 2005 10:10 pm    Post subject: Sudoku San - Ferocious 18-Aug-2005 Reply with quote

I had a look at this linked site and came across their 18 August puzzle.
Rising to the bait of the "ferocious" status and not having used the site
previously I had a go.

I reached the following.
Can anyone suggest how to proceed?

524 973 186
197 486 532
638 -1- 749

941 7-3 2-8
872 4-1 9-3
365 829 417

413 697 825
786 -4- 391
259 138 674

I accept that I may have erred in reaching the above position and so
I give the start position as a challenge for someone else to derive the
full solution.

-24 --- ---
--7 -8- -3-
6-- -1- --9

--- 7-- 2-8
--- --- ---
3-5 --9 ---

4-- -9- --5
-8- -4- 3--
--- --- 67-

Only 19 initial values given - but should be soluble??

As a result of my experiences with this one, I have now declined to use
Sudoku San as a source of puzzles - preferring the "Daily" dose!
Can anyone restore my faith in the other site?
Where did I go wrong - before or after reaching 75 of the 81 cells?

Alan Rayner BS23 2QT
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PostPosted: Thu Sep 22, 2005 10:18 pm    Post subject: Reply with quote

Tienes dos 4 en la tercera columna.
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chobans



Joined: 21 Aug 2005
Posts: 39

PostPosted: Thu Sep 22, 2005 10:40 pm    Post subject: Reply with quote

Yeah, you have two 4s at column 4. Your solution was almost way off from the final answer. That column 4 probably messed you up.
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Fri Sep 23, 2005 12:52 am    Post subject: Starting at the beginning ... Reply with quote

Hi, Alan!

I note, first, that the starting grid you exhibited contains 22 numbers, and not 19.

Here's what I've arrived at, after 12 moves. All of this agrees with the final, contradictory state you posted above. I'm pretty sure of all these moves, so you probably didn't make a mistake in the early going. Smile
Code:

- 2 4  - 7 -  - - -
- - 7  - 8 -  - 3 -
6 - -  - 1 -  7 - 9

- - -  7 - -  2 - 8
- 7 -  - - -  9 - 3
3 - 5  8 - 9  - - 7

4 - -  - 9 7  - - 5
7 8 -  - 4 -  3 9 -
- - -  - - 8  6 7 4


Just in case anyone else is following along, here's the sequence of moves. I think all of these are fairly obvious.

1. "3" at r5c9.
2. "4" at r9c9.
3. "9" at r8c8.
4. "9" at r5c7.
5. "7" at r1c5.
6. "7" at r3c7.
7. "7" at r6c9.
8. "7" at r5c2. This one wasn't so obvious. I had to locate the {2/8} pair in r5c1/r5c3 first.
9. "7" at r8c1.
10. "7" at r7c6.
11. "8" at r6c4.
12. "8" at r9c4.

If there are any more simple moves at this point, I'm not seeing them right now. Will let you know what else I figure out tomorrow sometime -- it''s time to go cook dinner. dcb
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geoff h



Joined: 07 Aug 2005
Posts: 58
Location: Sydney

PostPosted: Fri Sep 23, 2005 2:32 am    Post subject: Reply with quote

Hi all,

Yes, I agree with David's moves so far. Remainign steps are as follows:

1. You can quickly place Nr 2 in r6c5 as this is the only cell in Row 6 where you can place a 2.

2. Now consider Box 7. Nr 5 MUST be in either r9c1 or r9c2. Therefore, all other 5s can be eliminated from Row 9. Therefore, r9c5 must be a 3.

3. This leads to a pair of 5,6 in r4c5 and r5c5 which quickly means you can place a 3 in r4c6.

4. The puzzle is easily solved from this point. You can place a 3 in r1c4 and then a 9 in r1c1 and so on from there.


Cheers,
Geoff.
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Fri Sep 23, 2005 12:59 pm    Post subject: Order of moves Reply with quote

With Geoff's able assistance, I've now completed the puzzle. Looking at the grid that Alan posted to start this topic, it appears that his error occurred rather early -- around the 17th or 18th move, probably.

Here's the position from my previous post.
Code:

- 2 4  - 7 -  - - -
- - 7  - 8 -  - 3 -
6 - -  - 1 -  7 - 9

- - -  7 - -  2 - 8
- 7 -  - - -  9 - 3
3 - 5  8 - 9  - - 7

4 - -  - 9 7  - - 5
7 8 -  - 4 -  3 9 -
- - -  - - 8  6 7 4

Here are the moves that Geoff pointed out. Keep in mind that we've already located a {2, 8} pair in row 5, at r5c1/r5c3.

13. "2" at r6c5 ("2"s already placed in rows 4 and 5, because of the pair)
14. "3" at r9c5 (because "5" must appear at either r9c1 or r9c2, and the only values missing in column 5 are {3, 5, 6})
15. "3" at r4c6 (because {5, 6} pair must now appear in r4c5/r5c5}
16. "3" at r1c4 (because it can't fit anywhere else in the first row)
17. "9" at r2c4 (it can't fit anywhere else in top middle 3x3 box)
18. "9" at r1c1 (because of "9"s in rows 2 & 3).

At this point the grid looks like this:
Code:

9 2 4  3 7 -  - - -
- - 7  9 8 -  - 3 -
6 - -  - 1 -  7 - 9

- - -  7 - 3  2 - 8
- 7 -  - - -  9 - 3
3 - 5  8 2 9  - - 7

4 - -  - 9 7  - - 5
7 8 -  - 4 -  3 9 -
- - -  - 3 8  6 7 4


Differences between this position and the one Alan reached are fairly obvious. If I had to guess, I'd say you maybe wrote the "3" in r1c4 on the wrong side of the 7 at r1c5, Alan. Maybe not, but that's the sort of mistake I tend to make when I get in a hurry. dcb Smile
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