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"Probably Too Hard" by Hirofumi Fujiwara

 
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chuckfresno

Joined: 16 Jun 2005
Posts: 39
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PostPosted: Mon Aug 08, 2005 2:24 pm    Post subject: "Probably Too Hard" by Hirofumi Fujiwara Reply with quote

Code:

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


This one was composed by Hirofumi Fujiwara, a long time puzzle composer and programmer for Nikoli. The puzzles that are normally published are never hard by the standards set here. He called this one "Probably Too Hard" and placed it here.
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dukuso

Joined: 14 Jul 2005
Posts: 424
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Location: germany

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PostPosted: Mon Aug 08, 2005 6:03 pm    Post subject: Reply with quote

takes my solver 0.5ms
normal is less than 0.2ms
my 50 hardest ones take 0.9ms in average
currently hardest with 2.8ms is this one:

....1.78.5....9..........4..26.........6....3.74.8.........3..2.8..4..1.6..5.....
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nj3h

Joined: 29 Jul 2005
Posts: 9
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Location: Virginia - USA

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PostPosted: Mon Aug 08, 2005 8:59 pm    Post subject: Reply with quote

Unless I typed it in wrong, Pappocom indicates it is not a valid puzzle. Simes' solver will not solve it. As Simes' website indicates, he has not implemented some of the techniques as of yet, so I suspect that must be the reason there.
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angusj
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Joined: 18 Jun 2005
Posts: 406
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PostPosted: Mon Aug 08, 2005 10:56 pm    Post subject: Reply with quote

nj3h wrote:
Unless I typed it in wrong, Pappocom indicates it is not a valid puzzle.

It has a single solution, so in that (the most important) sense it's valid.
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kranser

Joined: 18 Aug 2005
Posts: 35
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PostPosted: Thu Aug 18, 2005 2:05 pm    Post subject: Reply with quote

angusj wrote:
nj3h wrote:
Unless I typed it in wrong, Pappocom indicates it is not a valid puzzle.

It has a single solution, so in that (the most important) sense it's valid.


I thought that a valid 9X9 puzzle had to have at least 23 starting values. I haven't read this whole forum yet, so please forgive me if this topic has been covered already.

What patterns does this puzzle require to solve?

Kranser.
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Merri

Joined: 02 Aug 2005
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PostPosted: Thu Aug 18, 2005 3:46 pm    Post subject: Reply with quote

A valid 9 x 9 puzzle can have as few as 17 starting values and still have only one solution. You can find these on this forum by searching for "minimal sudoku".
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kranser

Joined: 18 Aug 2005
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PostPosted: Thu Aug 18, 2005 4:26 pm    Post subject: Reply with quote

Merri wrote:
A valid 9 x 9 puzzle can have as few as 17 starting values and still have only one solution. You can find these on this forum by searching for "minimal sudoku".


Thanks Merri for your reply. Do minimal sudoku's require guess to be made when they are solved, or can they be solved purely by logic patterns?
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Merri

Joined: 02 Aug 2005
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PostPosted: Thu Aug 18, 2005 8:16 pm    Post subject: Reply with quote

You'll have to ask that from the people who create logics that require no guessing. Probably there is always a logic to solve a sudoku. Since I haven't such a logic in my hands, I can't really give a definite answer. However there are some 17 clues puzzles that can be solved with the most basic logics.
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chuckfresno

Joined: 16 Jun 2005
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PostPosted: Sat Aug 20, 2005 2:30 am    Post subject: Reply with quote

kranser wrote:
Merri wrote:
A valid 9 x 9 puzzle can have as few as 17 starting values and still have only one solution. You can find these on this forum by searching for "minimal sudoku".


Thanks Merri for your reply. Do minimal sudoku's require guess to be made when they are solved, or can they be solved purely by logic patterns?


My personal experience is that 17-clue Sudokus are usually on the easy side, for example this one chosen at random requires only the simplest of beginner logic.

The more general question of whether any particular Sudoku can be solved "purely by logic patterns" depends completely on what methods you include.
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