Saturday, December 02, 2006
AI Escargot -vwv

This is AI Escargot, supposedly the hardest Sudoku puzzle in the world to date. It does not have the least number of numbers provided but its creator, Finnish mathematician Arto Inkala designed it in such a way that requires player to consider "8 casual relationships simultaneously", whatever that means.

Being the ambitious guy that I am in such matters, I decided to give it a try. After an hour, my puzzle was covered with so many cancellations that I had to start over on a clean sheet. I have clearly underestimated its difficulty. This puzzle is driving me insane.

I took a 5 minutes break and started again. The only puzzles I have ever done are those in newspapers, which are really quite easy, so I don't know any techniques for handling multiple possibilities. I decided to try the branch-when-stuck-and-test-systematically approach. As you can see in my workings, I had to go 4 levels deep, that's pretty hard core for me. Due to a combination of luck and intelligent guessing, I only met 3 dead ends and didn't have to backtrack too far up. All these took another 1.5 hours.

And that's how I wasted a good Saturday afternoon.

-- permalink --
Yiheng made 6:53 PM

9 Comments:

Hardcore man. But at least you managed to solve it. I'm impressed.

Funny coincidence that for my division's retreat we also had a round of Sudoku as a warm-up exercise.
By  Soqcrates, at 1:39 AM  

I solved it in 17 minutes. I've had harder.
By  Unknown, at 1:11 PM  

Waw, that's great that you could solve it dude.. two thumbs up for you :)

I think it's a very hard hard one.. really make me headache.

Till I find and work it out through sudoku solver and DONE, it only took around 1-2 seconds and I got the answer ahahahahahaa lol :p

You'd better visit that site guys, www.sudokusolver.co.nr

It's quite a nice site I guess,
By  Anonymous, at 9:46 AM  

Well, apparently you worked it out the way my php script did it. My program also had to guess 4 levels deep.


It was my goal to write a program that would solve the toughest sudokus, and I did it! Though I'd really like to try this with pencil and paper like you did... so I've been trying to only glance quickly whenever I see the answer.

And I don't believe Mika.
By  Stephen, at 7:03 AM  

I discovered this puzzle when I did a google search “most difficult sudoku,” the search returned an article about AI Escargot. So I copied it down and solved it in about 20 minutes or so. Disappointed at how easy it was, I was relieved to discover it wasn’t the real AI Escargot, so I found the real one.

Very difficult puzzle, took me about 3 to 3.5 hours to solve. Definitely the most difficult puzzle I’ve ever tried. The first pass only gives one definite answer and two blocks with two possibilities. The first assumption had me considering 4 possibilities simultaneously before I could prove it false. Once I had that value the next output of possible answers gave 4 blocks with only two answers. From that point I was able to create a table for the four blocks with 16 possible unique answers sets; the fourth set of answers actually solved the puzzle. All in all I had to consider 6 possible answers simultaneously.

Mika, I don’t believe anyone can solve this puzzle in 17 minutes on the first try. Prove me wrong……How did you do it? What were your logic assumptions?

-Brian
By  Anonymous, at 2:37 AM  

Also http://www.sudokubrain.net/ solves it in a fraction of a second.
By  Anonymous, at 10:51 PM  

There is a difference between guessing a solution, and proving that the solution you have is unique.

By using regular techniques you know that each number is the only possible one at that particular place when you put it down, so when you are done you know you have the only possible solution.

By guessing, running into a contradiction and then repeating until it works, you don't know wether something else would have worked too.

Of course the puzzle is constructed so that it wouldn't, but you haven't proved that.
By  Feld, at 10:49 PM  

Result:
157 496 328
638 712 549
249 538 617

816 357 492
524 189 736
793 264 851

465 971 283
972 843 165
381 625 974
By  Anonymous, at 8:33 PM  

Troll
By  Unknown, at 6:20 AM  

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