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"hard". That means: not easy, right?

 
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Mon May 05, 2008 6:18 pm    Post subject: "hard". That means: not easy, right? Reply with quote
This puzzle can be solved by basic means - if "basic means" include finding a hidden quad Smile

Code:
+-----------+-----------+-----------+
|  7  .  .  |  2  4  5  |  .  .  .  |
|  .  .  .  |  .  .  .  |  .  .  .  |
|  8  3  .  |  .  .  .  |  .  9  4  |
+-----------+-----------+-----------+
|  9  .  .  |  .  .  8  |  .  7  .  |
|  .  .  .  |  5  .  6  |  .  .  .  |
|  .  1  .  |  7  .  .  |  .  .  3  |
+-----------+-----------+-----------+
|  1  7  .  |  .  .  .  |  .  4  9  |
|  .  .  .  |  .  .  .  |  .  .  .  |
|  .  .  .  |  6  2  1  |  .  .  8  |
+-----------+-----------+-----------+

play online
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storm_norm



Joined: 18 Oct 2007
Posts: 1741
PostPosted: Mon May 05, 2008 8:26 pm    Post subject: Reply with quote
Code:
.---------------------.---------------------.---------------------.
| 7      69     169   | 2      4      5     | 8      3      16    |
| 2456   2456   12456 | 3      8      9     | 1256   126    7     |
| 8      3      25    | 1      6      7     | 25     9      4     |
:---------------------+---------------------+---------------------:
| 9      26     236   | 4      13     8     | 126    7      5     |
| 234    248    7     | 5      13     6     | 9      128    12    |
| 56     1      568   | 7      9      2     | 4      68     3     |
:---------------------+---------------------+---------------------:
| 1      7      26    | 8      5      3     | 26     4      9     |
| 256    2568   2568  | 9      7      4     | 3      126    126   |
| 34     49     349   | 6      2      1     | 7      5      8     |
'---------------------'---------------------'---------------------'


i get to this point and I see an x-wing on 2.
I kind of quit looking for quads.

then the x-wing on 6 should solve it.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Mon May 05, 2008 8:38 pm    Post subject: Reply with quote
Sorry I think I misled you guys. It is not a hidden, but a naked quad (but well hidden Very Happy )
That said, as an apology, I offer this hint: the quad is visible in Norm's grid.
And there is a cell that contains all 4 candidates (which limits the number of eligible rows, cols and boxes)

I did say it was hard, didn't I ? Twisted Evil

P.S. this puzzle was in today's paper. Could not finish it at breakfast. Could not finish it before dinner. Took me a loooooong time. This one's a real stinker. But no "advanced" moves needed.
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Victor



Joined: 29 Sep 2005
Posts: 207
Location: NI
PostPosted: Mon May 05, 2008 8:49 pm    Post subject: Reply with quote
I think this is Norm's grid, without candidates, which can certainly be reached without pencil marks:
Code:

+-------+-------+-------+
| 7 . . | 2 4 5 | 8 3 . |
| . . . | 3 8 9 | . . 7 |
| 8 3 . | 1 6 7 | . 9 4 |
+-------+-------+-------+
| 9 . . | 4 . 8 | . 7 5 |
| . . 7 | 5 . 6 | 9 . . |
| . 1 . | 7 9 2 | 4 . 3 |
+-------+-------+-------+
| 1 7 . | 8 5 3 | . 4 9 |
| . . . | 9 7 4 | 3 . . |
| . . . | 6 2 1 | 7 5 8 |
+-------+-------+-------+

I don't think I'd have seen this without your hint, but I started to look . . .
. . . If you look across the rows as they see c3, you'll see that there are four rows containing 1349 (counting r8 which has 1 as a pointing pair in c89). So you can fill these numbers in the remaining spaces in c3, and fill the ones seen by 1349 with the other 4 numbers, 2568.
Thanks, good fun!

PS. I do think it's often easier to see X-wings before you write in / do a sweep of candidate numbers: see how obvious the X-wing in 2s in r3 & r7 is.

PPS.
Quote:
It is not a hidden, but a naked quad
Right both times! - there's one of each.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Mon May 05, 2008 8:54 pm    Post subject: Reply with quote
Victor wrote:

PPS.
Quote:
It is not a hidden, but a naked quad
Right both times! - there's one of each.


... and in the same house, too! Hidden and naked ... o tempora, o mores!
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