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what is the hardest known suduko ?
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thermosome

Joined: 22 Dec 2005
Posts: 2
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Location: San Francisco

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PostPosted: Fri Dec 23, 2005 5:40 am    Post subject: Reply with quote

Thanks gsf for your comments. I didn't explain in my earlier post exactly what kind of search I did on the 17-clue puzzles. I used breadth first with only F constraints, not FN constraints as you describe.

Tom
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Elizabeth Daniel

Joined: 27 Dec 2005
Posts: 2
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PostPosted: Tue Dec 27, 2005 7:47 am    Post subject: Why not use this free Sudoku host to post our Sudokus? Reply with quote

Hi All,

I have been using this free Sudoku host http://www.freesudokuhost.com recently, and found it quite useful to email or post Sudokus. Why not we use it rather than type '.'s and '-'s?
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tarek

Joined: 31 Dec 2005
Posts: 212
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Location: London, UK

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PostPosted: Sat Dec 31, 2005 4:29 pm    Post subject: Reply with quote

My solver seems to find these 2 grids the hardest of all grids.

Top 1465 #130
Code:
 5 . . | 4 . . | 8 . . 
 . . . | . 9 . | . 1 . 
 . . 2 | . . 1 | . . 5 
-------+-------+------
 6 . . | 3 . . | 4 . . 
 . 5 . | . 7 . | . . . 
 . . 4 | . . . | . . 8 
-------+-------+------
 3 . . | 6 . . | 7 . . 
 . 6 . | . . . | . 8 . 
 . . 8 | . . 2 | . . 1


Top 1465 #77
Code:
 7 . . | . . . | 4 . . 
 . 2 . | . 7 . | . 8 . 
 . . 3 | . . 8 | . . 9 
-------+-------+------
 . . . | 5 . . | 3 . . 
 . 6 . | . 2 . | . 9 . 
 . . 1 | . . 7 | . . 6 
-------+-------+------
 . . . | 3 . . | 9 . . 
 . 3 . | . 4 . | . 6 . 
 . . 9 | . . 1 | . . 5
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tarek

Joined: 31 Dec 2005
Posts: 212
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Location: London, UK

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PostPosted: Tue Nov 14, 2006 8:54 am    Post subject: Reply with quote

Things have changed dramatically since my post above......

ravel on the players forum has started a thread to collect all HARDEST sudokus.... All what were known as hardest to that date fell under the knife.... with amazing results....

Since then several HARDEST puzzles have came into focus (All new & unpublished) attempting to claim the crown......

One of the recent attempts was ArtoI's "Etana", which went into the newspapers as the hardest (although NOT according to the players forum).........

How do you rate these Ultra hard puzzles ...... Players have been using the Sudoku explainer,gsf's sudoku & dukosu's suexrat9 & ravel would then try to find the shortest brute force (contradiction eimination) path to solving the puzzle.

As this is a programmers forum, I'm sure that there are many who are up for the challenge to produce more difficult puzzles Twisted Evil

here are the puzzles compiled by ravel to date....you can refer to the thread HERE to know the author of the puzzle & the discussion on the hardest puzzles there.

The list until this moment stands at:
Code:
600001900080030000001700002002000007050000010400000300300009600000040080008200005
000001002010020030400500000004000006070030010800000900500008000000010070006400500
001000200030040050600000007000103000080000030000604000200000006040050080007000100
001000002030040000500600300004007001000080030900200600000008009070020040200100800
000001002030040050600700000005000004080020090700000300100004000000050080009600700
000001002030020040500600000003000007010080020400700500600004000000060010007300900
001002003020040010500600000000007001030080020400500600005009002070000080300000900
100000002020030040005000600000307000040010030000805000008000500030020090600000001
000001002030040050600200000005000007070030040200000600100008000000070090004600800
000500700020060040006001003900200400030000010007003008100700600050040070009008000
000001002030020040500600000007000003010040080600000500900006000000070030008500900
001002003020040010500600200000007000080010020400500600005009008070000040800000900
001000002030040000500600300007008001060010030100900800005009004080050070200100900
000001000010020030400500100006007003080030010200900400009000002070080060800300500
000001002030040050600700000005000004070080030200000600100006000000050070003900800
000001002020030040500600000007000008090040020600800500900008000000090030006700100
005000009020030040000600800004900001000040060700008900003001008070060090500200600
700000400020070080003008009000500300060020090001007006000300900030040060009001005
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700009800090030040005600001006000009040000030200000100100008700050040010007200005
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900004300040030020005900001007000004020000010800000600600003100050040070009800005
000300500050010030007004001200000400060090000001006002800700200090080050005009007
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600001900080030000001700002002000007050000010400000300300009400000040080008200005
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200003700000060040009500008007005001080070060500200800100000300070020050004900007
000001002020030040500600000003000007080040020600700900800006000000050080005900300
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100000009007080006000300050000040800700001000096000000008200000500000063060070400
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009005006070030040800600300000108005040000080000006100008009004000000020300500600
000007000010090060900600700009400002050030000200800400004005007030000010700300900
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500008900010000000004600007009300005000070060200000400400009802050080040003400500
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002004005030060000000700600000009001090050030400200800001005002050040090700800000
000006000060090010100500700003002009020060030700300800009007008070040000500000300
400008300060090040008100006003800004050060090600003200100000005070080030004700000
800005900040060030006100008001500007080070000900003000500002300060000040008000705
006003000090010080300500000003009001020030050500800900007004005030090020400000700
000007900030060040008500000000100005000040030600009400400001602020000090007200100
100007000030020050005600002000300007040080030800005900200000301010000000007900406
200000900070040020008100004001300006000010080900006500700003005050070030009200400
500007900090050040001200000004000006060030050100004800700003200030070090005800307
800007900040010060000500000006000002020030070900002800700003100010080000005100304
000004700000030060000200009005000001090080030300007600100006004070090020002300100
000003800020050000000700004006400001000030090700001300500000900080070030001200006
400008500080030000001900002008100005030060020000004700900007000050000060002500004
500000600010080020002400009005200001070000080400009000000003105000070030007500200
500008000030000060009000005000300008010020000600005400400007500020060080007500109
500008000030050060009000000000300008010020050600005400400007500020060080007000109
500008000030050060009000005000300008010020000600005400400007500020060080007000109
200005900090040020003000006007100008040060090000009100600008007000020030005000800
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000007100020060090001900008009700000030020060000004800400003200010070000008400705
007005008060010040300600000001006005020080070800500200000009003070000050600200800
100007090030020008009600500005300900010080002600004000300000010040000007007000300
001002003020040010500600700006000004080000090300000200003001009090060020700800500
000002003020040010500100600007000004010000080300000200005003002080070090600200500
001002003000040010500600700003000004060000080900000200005007002080030070700200500
001002003020040010300500600005000004070000080900000500000001009080050070600700300
001002003020040050600700800005000004090000070300000200006008000010050090800200600
001002000020030040400500300003000005060000070800000100002003009070080060000100800
001002000020030040400500600006000005030000070800000100002005009070010030000900800
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001000200030000040400050006000102000060030070000708000300000005050040030002000800
001000200030000040500060007000108000070030050000209000400000003060040070009000800
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001002000030040050500600700007000006010000080900000200003007001080010040000500900
600009800050030000002500007007000009010000020400000300300008600000040080009700001
100005600060030000002900007007000009080000020400000300300009100000040060005700008
900006800050030000001700009002000007070000020400000300300008900000040060005200001
100004600060030000007500009009000002050000070400000300300008100000040020008200005
600004900080030000005100002002000007010000050400000800300008600000040070007200009
800006700050030000001400005009000002030000060400000100600007800000040050002900003
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001002000030040050600700800006000007010000020900000500003001006040050030000800900
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001002000030040050500600700007000006040000080900000200002001003080030010000700500
001002000030040050500600700007000008010000030900000600008003001040010020000500900
001002000030040050500600700007000006080000040900000100004008003020030080000700900
001002000030040050500600700008000006010000020900000500002001004070030010000800600
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001002000030040050500600100007000006080000090400000300006007002090030080000100400
000003090000010057000500862000000009060000080302000700005204000180070000400008000
001002000030040050004700800006000007010000030900000600007001008040030020060500900
900001800060030000002500007009000006050000020400000300300008100000040080007900005
060900003500004020000080400800000050003000700090000001001050000070300009900002040
001002000030040050600700800008000007010000030900000500002001006040050020000600900


tarek
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humbertoldi

Joined: 24 Nov 2006
Posts: 1
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PostPosted: Fri Nov 24, 2006 4:47 pm    Post subject: soduko solver Reply with quote

Hello there,

I have just written a soduko solver in ANSI C. I tried it on several of the supposedly most difficult sodukos on this site, and it works fine.

The logical methods implemented are rather simple (no X-Wing, pairs and other fancy stuff). If these methods alone are not sufficient, the program solves by (recursive) guessing.

If you want to have the source code, just email me at humbertoldi at yahoo dot fr.

Cheers.
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tarek

Joined: 31 Dec 2005
Posts: 212
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Location: London, UK

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PostPosted: Sat Nov 25, 2006 12:03 pm    Post subject: Reply with quote

I'm sure that you caught by what I described as hardest ..... that it is the hardest for a human to solve.......

a machine using DLX or backtracking will solve any puzzle in a fraction of a second.......machines employing "fancy" techniques still need a fraction of a second to solve any puzzle

contradiction elimination has a place in human solving methods but it should be last......

hardest doesn't mean impossible to solve, but hardest to get to the solution..........

tarek
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kammi

Joined: 27 Nov 2006
Posts: 7
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Location: www.sudokupower.com

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PostPosted: Thu Feb 08, 2007 8:38 pm    Post subject: my hardest sudoku's Reply with quote

Hi,

these will probably not score as the hardest sudoku's ever...

008000300004017000019020000000004050080050009000600780300200070920546000000000005
080900060001060000000105030005000983300090207000200000007480002900000400000071000
000030190000900004080000000000000700002019030306007008024000015108006000000040070
007000000000010030020000000009100004035000060160090050001004003650000907090806500
000000000009074200280000050000002036000600002050010080060000000890130000320009004
500000040070080060300000800000030002860100300000407000000370910040090020001000005

however they are my hardest self generated sudoku's. As i'm not certain i have a foolproof rating algorithm i am wondering how difficult these sudoku's realley are. Who would like to check

Regards
Arnold
(owner of sudokupower dot com)
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m_b_metcalf

Joined: 13 Mar 2006
Posts: 341
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Location: Europe

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PostPosted: Fri Feb 09, 2007 1:44 pm    Post subject: Re: my hardest sudoku's Reply with quote

kammi wrote:
Hi,
however they are my hardest self generated sudoku's. As i'm not certain i have a foolproof rating algorithm i am wondering how difficult these sudoku's realley are. Who would like to check

A widely accepted means of comparison is Sudoku Explainer which rates on a scale of 1 to 11+. This you can easily try it yourself. Anything below 10 is no longer regarded as 'difficult'. Another is gsfr. Please also visit the Sudoku Players' Forum for much more information.

Regards,

Mike Metcalf
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kammi

Joined: 27 Nov 2006
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PostPosted: Sat Feb 10, 2007 6:43 am    Post subject: Reply with quote

thnx! The Sudoku Explainer gives great analysis!
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rmessenger

Joined: 08 Mar 2007
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PostPosted: Thu Mar 08, 2007 4:33 am    Post subject: Simple solution Reply with quote

I have a simple (relatively) python script that has solved every one of the posted examples (and all others I can find) in less than ten seconds, (on a modest machine). If anyone is interested, email me at rmessenger(at)gmail(dot)com
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kammi

Joined: 27 Nov 2006
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PostPosted: Mon Mar 12, 2007 7:41 pm    Post subject: Reply with quote

Hi Rmessenger

The complexity of a Sudoku is not a result of the solving time of a script. Solving any Sudoku using my own built solver software solvers takes 0.2 seconds max.

This software recognizes patterns, so it can eliminate candidates just as long until a solution is found (and if not: Everything remaining option is brute-forced using a technique called Ariadne's thread)

The software is fast, because a CPU has very little trouble finding all kinds of patterns, bacause there is enough CPU power to try all kinds of combinations. A human however does not have this computing power. So the question is: Which pattern is difficult and which one isn't ?

Regards
Arnold
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north55

Joined: 02 Dec 2006
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PostPosted: Tue Mar 13, 2007 6:30 am    Post subject: Re: my hardest sudoku's Reply with quote

m_b_metcalf wrote:
Anything below 10 is no longer regarded as 'difficult'.Regards,

Mike Metcalf


? Pardon?

This seems untrue. Most people can now solve puzzles up to level 10 in SE???

Wow. I am certainly not "most people".
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m_b_metcalf

Joined: 13 Mar 2006
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PostPosted: Tue Mar 13, 2007 12:29 pm    Post subject: Re: my hardest sudoku's Reply with quote

north55 wrote:
m_b_metcalf wrote:
Anything below 10 is no longer regarded as 'difficult'.Regards,

Mike Metcalf


? Pardon?

This seems untrue. Most people can now solve puzzles up to level 10 in SE???

Wow. I am certainly not "most people".

I meant this in the sense that there are now many known puzzles at > SE 10.0. Thus, if we're talking about the 'hardest known sudokus' (the subject of this thread), anything below no longer really qualifies. Please see the corresponding thread on the Players' Forum where there is much discussion on this topic including:
Code:

 5 . . . . . . . 9
 . 2 . 1 . . . 7 .
 . . 8 . . . 3 . .
 . 4 . 7 . 2 . . . 
 . . . . 5 . . . .
 . . . . . 6 . 1 .
 . . 3 . . . 8 . .
 . 6 . . . 4 . 2 .
 9 . . . . . . . 5   SE  11.4

Whether or not a human can solve them is another matter (I can't Sad ).

Regards,

Mike Metcalf
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rickhev1

Joined: 30 May 2007
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Location: Columbia, SC, USA

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PostPosted: Wed May 30, 2007 1:13 pm    Post subject: A new candidate for hardest Reply with quote

Here is the hardest sudoku I have encountered. It is by JPF and is rated 11.4 by SE. Mike Metcalf's above is the next hardest one I know of.

1 0 0 0 0 0 0 0 2
0 9 0 4 0 0 0 5 0
0 0 6 0 0 0 7 0 0
0 5 0 9 0 3 0 0 0
0 0 0 0 7 0 0 0 0
0 0 0 8 5 0 0 4 0
7 0 0 0 0 0 6 0 0
0 3 0 0 0 9 0 8 0
0 0 2 0 0 0 0 0 1

Best regards,
Rick Hevener
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Mosc_007

Joined: 06 Jun 2007
Posts: 6
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PostPosted: Fri Jun 08, 2007 4:46 pm    Post subject: Reply with quote

Looks like a lot of you guys are into writing your own programs to either solve or create Sudoku puzzles. I have been into Sudoku for some time and am addicted to it. I love playing Extreme level in Simple Sudoku and nearly always get them out.

I also have a heap of experiance programming. Writing a program to solve them seems to defeat the purpose of the game. However writing a program to create them could be a lot of fun.


Charles
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