what is the hardest known suduko ?

thermosome · Posted: Fri Dec 23, 2005 5:40 am Post subject:

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

Elizabeth Daniel

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?

tarek · Posted: Sat Dec 31, 2005 4:29 pm Post subject:

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

Top 1465 #130

tarek · Posted: Tue Nov 14, 2006 8:54 am Post subject:

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Since then several HARDEST puzzles have came into focus (All new & unpublished) attempting to claim the crown......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

humbertoldi · Posted: Fri Nov 24, 2006 4:47 pm Post subject: soduko solver

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.

tarek · Posted: Sat Nov 25, 2006 12:03 pm Post subject:

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

kammi · Posted: Thu Feb 08, 2007 8:38 pm Post subject: my hardest sudoku's

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)

m_b_metcalf · Posted: Fri Feb 09, 2007 1:44 pm Post subject: Re: my hardest sudoku's

kammi · Posted: Sat Feb 10, 2007 6:43 am Post subject:

thnx! The Sudoku Explainer gives great analysis!

rmessenger · Posted: Thu Mar 08, 2007 4:33 am Post subject: Simple solution

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

kammi · Posted: Mon Mar 12, 2007 7:41 pm Post subject:

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

north55 · Posted: Tue Mar 13, 2007 6:30 am Post subject: Re: my hardest sudoku's

m_b_metcalf · Posted: Tue Mar 13, 2007 12:29 pm Post subject: Re: my hardest sudoku's

rickhev1 · Posted: Wed May 30, 2007 1:13 pm Post subject: A new candidate for hardest

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

Mosc_007 · Posted: Fri Jun 08, 2007 4:46 pm Post subject:

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