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March 28 Hard - Try it !

 
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cgordon



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

PostPosted: Fri Mar 28, 2008 2:39 pm    Post subject: March 28 Hard - Try it ! Reply with quote

The Hard sudokus are rarely discussed in the forums because they involve no advanced techniques. But often they are quite challenging in their own way. I thought todayís was a good one. There are no 9ís for a start.
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Fri Mar 28, 2008 3:46 pm    Post subject: Reply with quote

I don't understand how people solve any of these puzzles (except maybe the "easy" ones) in just a matter of minutes. Actually, it seems like the VH puzzles are usually easier than the hard--or oftentimes even medium puzzles to get through a lot of the basics.

This hard puzzle took me a LONG time to resolve. I had to use an x-wing (or did I use 2 x-wings altogether? I can't entirely remember now) to finally crack the puzzle.

Did anyone actually solve this puzzle without using a wing?
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sdq_pete



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

PostPosted: Fri Mar 28, 2008 3:56 pm    Post subject: Reply with quote

I was wondering the same. It took me quite a time and I took recourse to a number of advanced techniques (W-wing, X-wing, XY-wing). Whether any of them were really necessary or not I don't know, but I seemed to need them to progress.

Peter
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Marty R.



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

PostPosted: Fri Mar 28, 2008 4:31 pm    Post subject: Reply with quote

Quote:
Did anyone actually solve this puzzle without using a wing?

Yes. I can't provide any details, it was just subsets and locked candidates, although this one might've been a little more stubborn than most.
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cgordon



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

PostPosted: Fri Mar 28, 2008 4:37 pm    Post subject: Reply with quote

I believe by definition, the Hards should not require wings. I used basic stuff for this one but it took me a while. Looking at the 9's in the middle box finally did it.

Last edited by cgordon on Fri Mar 28, 2008 6:01 pm; edited 1 time in total
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nataraj



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

PostPosted: Fri Mar 28, 2008 5:09 pm    Post subject: Reply with quote

I did the puzzle just now on paper.

No wings. Definitely.

First breakthru when I spotted the naked pairs 19 and 68 in col 2, then NP 27 box 1/row 2 and naked triple 369 in col 6 which solved 2 and 4 in box 5. No major obstacles after that.
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nataraj



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

PostPosted: Fri Mar 28, 2008 6:49 pm    Post subject: Reply with quote

And to add a few words about timing - quote: "a matter of minutes":

this puzzle took me 21 minutes.
that is rather long for a "hard", but not excessive.
"hard" from this site or in my local paper, and "fiendish" in the London Times always can be solved by basic means and usually take me between 15 and 20 minutes.

When I reach 20 minutes for a "hard" and I am still stuck, I then decide that I am suffering from a mental block (my brain refuses to see the clues), I let it rest for like half a day and when I come back the puzzle solves itself Wink

When I solve a puzzle in under 14 minutes I am disappointed, because I feel that it was too easy Sad .

I cannot remember ever having solved a puzzle in less than 10 minutes (I don't do "easy" or "medium"). The initial phase ("sweeping the floors") alone takes a few minutes.

Of course, the online version, with auto-sweep on, allows much shorter times. But then, what is the point? I am not trying to prove how fast I can write or how fast I can click.
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keith



Joined: 19 Sep 2005
Posts: 3329
Location: near Detroit, Michigan, USA

PostPosted: Sun Mar 30, 2008 5:46 pm    Post subject: Reply with quote

This one is quite simple, once you see it! (But, yes, it took me quite a while.)

R7C6 is <5>, R3C1 is <8>.

The <2> and <7> in C2 force a pair <27> in B1 in R2.

Look at C6. R1C6 is <7>, and the <9> in B5 lies in C6.

Which solves R6C4 as <2>. All that remains is to recognize that there is a pair <19> in C2 and in R2.

Keith
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Victor



Joined: 29 Sep 2005
Posts: 207
Location: NI

PostPosted: Sun Mar 30, 2008 8:04 pm    Post subject: Reply with quote

Should do this more often! Like the good old days, when we didn't use candidate numbers, and some people even did puzzles without putting a single mark on the paper. I used to like Sudoku-san for puzzles like this - basics + X-wings, but I noticed recently that the site seems to have bit the dust, which is a pity.
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keith



Joined: 19 Sep 2005
Posts: 3329
Location: near Detroit, Michigan, USA

PostPosted: Sun Mar 30, 2008 10:34 pm    Post subject: Reply with quote

Victor wrote:
Should do this more often! Like the good old days, ...

Victor,

I still do this, when I can! If you look at the starting grid, the <27> pair is quite obvious after one sweep. The <19> pairs are also obvious without pencil marks.

But, I did not see the rest of it, and marked in the candidates before seeing C6 is the key.

If you want a source for the hardest puzzles that do not require advanced methods, (except maybe X-wings) try Fiendish Sudoku. I became a much better solver (of the basics) by doing these puzzles without pencil marks or, at most, with minimal PM's.

Here is the current most fiendish puzzle:

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


http://www.fiendishsudoku.com/sudoku.html

Best wishes,

Keith
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cgordon



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

PostPosted: Mon Mar 31, 2008 5:36 pm    Post subject: Reply with quote

As an interesting comparison, I did todayís Hard (31 Mar) in no time at all using the auto-sweep. Unlike Nataraj I have no compunctions about using auto-sweep - and would never, like Keith, attempt a puzzle without pencil marks. Itís like the old Masters - Rembrandt, Mike Angelo etc: they only did the good bits and had someone else prepare the canvas. Although it could also be my natural laziness.
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nataraj



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

PostPosted: Mon Mar 31, 2008 7:57 pm    Post subject: Reply with quote

Quote:
Like the good old days, when we didn't use candidate numbers, and some people even did puzzles without putting a single mark on the paper.


And we had sudoku, but without the grid, only a few numbers on a sheet of paper! Very Happy

just kidding of course...

There's this Dilbert episode, goes like this:

Wally and the guys: "[in the old days ...] we had to program in zeroes and ones, and sometimes we didnít even have ones. I once wrote a database program using only zeroes."

Laughing Laughing Laughing
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Tue Apr 01, 2008 12:01 am    Post subject: Reply with quote

[quote="nataraj"]
Quote:
There's this Dilbert episode, goes like this:
Wally and the guys: "[in the old days ...] we had to program in zeroes and ones, and sometimes we didnít even have ones. I once wrote a database program using only zeroes."



That is funnnnnnnnnnnnnnnnnnnnny
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Tue Apr 01, 2008 10:33 am    Post subject: Reply with quote

nataraj wrote:
I once wrote a database program using only zeroes."
Ah yeah, the good old times, when it was possible to write a program without any bugs Cool
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Victor



Joined: 29 Sep 2005
Posts: 207
Location: NI

PostPosted: Tue Apr 01, 2008 11:33 am    Post subject: Reply with quote

Thanks Keith. I haven't previously tried this site. Nice paper-and-pencil puzzle.
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