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3 Sep - V hard

 
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kathyjc



Joined: 03 Sep 2006
Posts: 2
Location: Trinidad, WI

PostPosted: Sun Sep 03, 2006 11:20 am    Post subject: 3 Sep - V hard Reply with quote

Hi,

Just need some help with the logic for this puzzle. This is where I have reached.


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

9 * * | 1 * * | 4 7 *
3 1 * | * * * | * 9 8
* 4 7 | * * 9 | 3 * 1

1 2 * | * * * | * 3 7
* * 9 | * * * | 1 4 *
4 7 3 | * 1 5 | * * 9

The hint feature places a 2 in the 4th row, 3rd col... but I am not sure why. And even when I take that hint I do not get much further before being stuck again. Any assistance with the logic would be appreciated.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sun Sep 03, 2006 12:29 pm    Post subject: Reply with quote

Kathjc,

Here is the grid with pencilmarks:

Code:
 
 *-----------------------------------------------------------*
 | 5     9     8     | 2     6     4     | 7     1     3     |
 | 7     6     4     | 358   358   1     | 9     25    25    |
 | 2     3     1     | 59    59    7     | 6     8     4     |
 |-------------------+-------------------+-------------------|
 | 9     58    256   | 1     2358  2368  | 4     7     256   |
 | 3     1     256   | 4567  2457  26    | 25    9     8     |
 | 68    4     7     | 568   258   9     | 3     256   1     |
 |-------------------+-------------------+-------------------|
 | 1     2     56    | 4689  489   68    | 58    3     7     |
 | 68    58    9     | 3678  2378  2368  | 1     4     256   |
 | 4     7     3     | 68    1     5     | 28    26    9     |
 *-----------------------------------------------------------*


Row 5 has a naked triple that eliminates the 5's from the rest of that row (r5c45). This makes an X-wing that excludes the 5 from r4c3.

Box 8 (lower middle) has a naked pair that eliminates all 6's from other cells in that box, which creates an X-wing that eliminates 6 from r4c3. That leaves 2 as the only candidate in that cell.


Last edited by TKiel on Sun Sep 03, 2006 12:33 pm; edited 2 times in total
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David



Joined: 02 Jun 2006
Posts: 58
Location: Bedford, UK

PostPosted: Sun Sep 03, 2006 12:32 pm    Post subject: Reply with quote

Hi Kathy

I think you will find the key to this puzzle is an 'X-wing' on 6's.
If you look at column4 there are only two cells which can hold a 6 (row6,9). Similarly on column8 there are only two cells for a 6 (rows 6,9) again. So you can eliminate the 6 from c1r6 (making it an 8) and the whole puzzle collapses from here
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gigi



Joined: 04 Jun 2006
Posts: 5
Location: Central Texas

PostPosted: Sun Sep 03, 2006 7:00 pm    Post subject: Reply with quote

I know there are many ways to solve the puzzle, but I was able to solve it without any of the advanced techniques (x-wings, etc). I didn't even have put in pencil marks until almost the end... and I'm a pencil mark user all of the time. I'm not sure why this was classified as a very hard??? Oh well... have a great long weekend, if you are lucky enough to be off!...

Laterz... gigi
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David Bryant



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

PostPosted: Sun Sep 03, 2006 11:17 pm    Post subject: How? Reply with quote

gigi wrote:
... I was able to solve it without any of the advanced techniques ...

I'd be very interested to learn how you did that, gigi. Can you explain it for us?

I got through the puzzle without making any pencil marks. I didn't use the X-Wings, either. But I did have to resort to a couple of double-implication chains, and I'd like to learn which simpler moves I overlooked. dcb
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Bill Denholm



Joined: 24 Mar 2006
Posts: 17
Location: Mountain View, California

PostPosted: Mon Sep 04, 2006 2:25 am    Post subject: Reply with quote

I usually use the traditional techniques, too, but I couldn't have solved this puzzle withoout the X-Wings.

Bill
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kathyjc



Joined: 03 Sep 2006
Posts: 2
Location: Trinidad, WI

PostPosted: Mon Sep 04, 2006 11:50 am    Post subject: Reply with quote

Thanks for the help. The "X-wings" clue helped a lot. I never looked for that before.
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