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Mon. Mar 31 HARD

 
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thebullroars



Joined: 04 Apr 2008
Posts: 4

PostPosted: Sun Apr 06, 2008 5:31 pm    Post subject: Mon. Mar 31 HARD Reply with quote

If people thought Mar. 28 was hard try Mar 31!Exclamation
The word hard is in cap's for a reason!Exclamation

I'm surprised no one had any comment on it! ExclamationSurprised

After putting it aside several times I finally got it!Exclamation Embarassed
I thought it was a good one in that it did not require
naked pairs to help to solve it! To me the technique
to solve it, is advanced, in that it is rarely used but
does not need any of the "official" advanced techniques!Exclamation

The Bullroars
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sun Apr 06, 2008 6:32 pm    Post subject: Reply with quote

Hi, welcome to the forum. I can't comment on the puzzle since I haven't done it. But feel free to join the party and make comments/ask questions as often as you'd like.
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Sun Apr 06, 2008 8:12 pm    Post subject: Reply with quote

This one wasn't so bad, I thought... You should reach the following position without too much work:
Code:

+--------------+-------------+--------------+
| 234 239 .    | 1   .  7    | 5   346  8   |
| 7   5   .    | 389 .  2346 | 1   346  469 |
| 6   1   3489 | 389 5  34   | 49  7    2   |
+--------------+-------------+--------------+
| 238 4   1239 | 6   37 5    | 289 28   17  |
| 5   269 7    | 4   1  8    | 3   26   69  |
| 38  36  136  | 2   37 9    | 468 5    17  |
+--------------+-------------+--------------+
| 1   8   26   | 5   4  26   | 7   9    3   |
| 234 7   5    | 389 .  236  | .   1    46  |
| 9   236 .    | 7   .  1    | .   2468 5   |
+--------------+-------------+--------------+

Play this puzzle online at the Daily Sudoku site
Then, the forced 4 at R6C7 makes it more or less fall apart. No advanced techniques!

Peter
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keith



Joined: 19 Sep 2005
Posts: 3331
Location: near Detroit, Michigan, USA

PostPosted: Sun Apr 06, 2008 8:17 pm    Post subject: Reply with quote

Where's that soapbox!

I think this is another illustration of a puzzle that gets much harder if you fill in all the candidate pencil marks. You should try to spot pairs by looking at the solved cells, not by examining pencil marks.

After filling in the singles you will see that there are solved cells <1> and <7> in C78 and in R5, all pointing at B6. So, R46C9 are a pair <17>, which places a <4> in R6C7, and you are done.

Code:
+-------------------+-------------------+-------------------+
| 234   239   2349  | 1     2369  7     | 5     346   8     |
| 7     5     23489 | 389   23689 2346  | 1     346   469   |
| 6     1     3489  | 389   5     34    | 49    7     2     |
+-------------------+-------------------+-------------------+
| 238   4     12389 | 6     37    5     | 289   28    179   |
| 5     269   7     | 4     1     8     | 3     26    69    |
| 38    36    1368  | 2     37    9     | 468   5     1467  |
+-------------------+-------------------+-------------------+
| 1     8     26    | 5     4     26    | 7     9     3     |
| 234   7     5     | 389   23689 236   | 2468  1     46    |
| 9     236   2346  | 7     2368  1     | 2468  2468  5     |
+-------------------+-------------------+-------------------+

By the way, today's (April 6) Hard puzzle took me a lot longer to solve than the Very Hards usually take. I think it is much harder than this one, if you use pencil and paper and no assistance from a computer.

Keith
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Mon Apr 07, 2008 2:08 am    Post subject: Reply with quote

There is no doubt from my experiences that hard puzzles (and sometimes mediums too) are not easy --- for me.
I don't remember how long it took for me, but I did solve the March 31 puzzle. Sometimes x-wings are available and useful to solve these. I know that wings are not supposed to be required in anything less than VH. I frequently understand the xy-wings and xyz-wings when pointed out, but there is simply slim to no chance I can find any of these kinds of wings on my own.

Another problem I have is seeing the lengthy chains pointed out by the geniuses in here. I do not have the power of concentration to follow a long chain through to see how it works out. It is like playing a chess game. I have always been a fair chess player, but I have never been able to look ahead 10 (or 100 or whatever) plays like real good chess players can do.

For me hard puzzles can normally be solved in 2 hours or less. I know that there are those who need only 20 minutes or less for any puzzle, but such people are math geniuses I am sure. I have a good math aptitude, but I am not a math genius.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Mon Apr 07, 2008 5:13 am    Post subject: Reply with quote

Quote:
I frequently understand the xy-wings and xyz-wings when pointed out, but there is simply slim to no chance I can find any of these kinds of wings on my own.

Crunched, if you're convinced that you can't find these, then maybe you won't be able to. But if you want to be able to find them, you can and will; it's not rocket science. If you need some tips, just ask, there are any number of people here who'd be happy to point you in the right direction.

Good luck.
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Mon Apr 07, 2008 12:40 pm    Post subject: Reply with quote

This was indeed a very tough "hard". The key to the puzzle (at least for me) was a quad 1367 in row 6, followed by another -very difficult to see - quad 2689 in box 6 which solved r6c7 like sdq_pete pointed out. Took me a long time.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Mon Apr 07, 2008 4:56 pm    Post subject: Reply with quote

Keith: I like that "trick" for finding hidden pairs. I usually find that harder than spotting the quads.

Meanwhile, a terrible famine has come upon us. Only two very hards in the last 14 days. That's cause for a lot of wailing and gnashing of teeth.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Mon Apr 07, 2008 5:20 pm    Post subject: Reply with quote

cgordon wrote:
Meanwhile, a terrible famine has come upon us. Only two very hards in the last 14 days. That's cause for a lot of wailing and gnashing of teeth.
One by gsf for the time waiting:
Code:
 +-------+-------+-------+
 | 8 . . | 3 . 1 | . . 2 |
 | . . . | . . . | . . . |
 | . . 7 | . 6 . | 9 . . |
 +-------+-------+-------+
 | 7 . . | . . . | . . 9 |
 | . . 6 | . 4 . | 5 . . |
 | 2 . . | . . . | . . 1 |
 +-------+-------+-------+
 | . . 9 | . 5 . | 3 . . |
 | . . . | . . . | . . . |
 | 1 . . | 2 . 3 | . . 8 |
 +-------+-------+-------+
>>> play online
[Edit:]I posted it in the "Other puzzles" forum for further discussions here.


Last edited by ravel on Tue Apr 08, 2008 1:50 pm; edited 1 time in total
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Mon Apr 07, 2008 7:59 pm    Post subject: Reply with quote

Ravel !!! What a most excellent Sudoku. Where did you find it? What is gsf?

I started off thinking you had missed a number on the grid but slowly I found 5 pairs (79/C5; 45/C3; 38/R6; two 4's/B4; two 5's/B4) and one triple <467> in C7. ..... and yet I still haven't made a single new entry!!!
-------
Edited Later:
Actually... Hold the praise! I used 2 UR's <467> C78 and eventually found some "no-solution" cells. It doesn't seem to work. Did you copy it right?? Couldn't possibly be me !
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Tue Apr 08, 2008 7:20 am    Post subject: Reply with quote

The puzzle is from the Patterns Game thread on the Players forum. They select a pattern and try to find as much as possible puzzles with different ratings.

The challenge with this one is to find the first number, because it needs some steps, which i would not be able to do without pencilmarks.

I also checked it with the online solver here to be sure, that it meets the VH criteria. So no UR's are required.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Tue Apr 08, 2008 1:25 pm    Post subject: Reply with quote

Quote:
I also checked it with the online solver here to be sure, that it meets the VH criteria. So no UR's are required.


Actually, a UR would put it in the VH category. However, I was wrong to state the UR above. That wasn't a UR. I did get so far with a couple of xy wings and a genuine UR - but then got stuck.

Maybe though this is the wrong forum though to pursue another puzzle.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Tue Apr 08, 2008 1:54 pm    Post subject: Reply with quote

cgordon wrote:
Maybe though this is the wrong forum though to pursue another puzzle.

You are right, i should have posted it to the "Other puzzles" forum and only provide a link here. I did it now and made this thread for further disussions.
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kragzy



Joined: 01 May 2007
Posts: 112
Location: Australia

PostPosted: Fri Apr 11, 2008 4:20 am    Post subject: Reply with quote

ravel,

Thanks for the elegant puzzle. So many seeming break-throughs, only to be confronted with a new challenge, time and again. Not only that, the puzzle retained a high degree of symmetry as cells were solved - as I said, how elegant. A pleasure to solve.

Cheers
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