## Monday, October 19, 2009

### Sudoku - Very Difficult Puzzles

Here is a page containing 4 very difficult Sudoku puzzles. I shall be printing a book of these puzzles, available in soft copy. If you like it, give your particulars here.

A Singaporean said...

This post is not to discredit your good work, but I think a lot of people doesn't know that there is always a group of people specializing on ultra-ultra-ultra-hard sudoku puzzles. So when you say that some of your puzzles are suitable only for "top experts", I find it a bit funny. I found that all of your hardest puzzles so far can be solved using the Simple Sudoku Technique Set (http://www.sudopedia.org/wiki/SSTS), which to that community are considered way too simple to even mention. You might be interested to learn a subset of the solving techniques those people use at Sudopedia (http://www.sudopedia.org/wiki/Solving_Technique). Keep up the good work though. =)

Tan Kin Lian said...

Hi
I remove reference to top experts. But can you try the 4 difficult puzzles and let me know if they can be solved by simple techniques.

Anonymous said...

Hi Mr. Tan
I tried the complex puzzles. They are difficult.

A Singaporean said...

Yes. These four puzzles can be solved using Simple Sudoku Technique Set (SSTS) alone.

It should be noted that some of the SSTS techniques are considered very advanced for the average person. So I do not challenge the "complex" difficulty label.

Tan Kin Lian said...

Hi
How long did you take to solve a complex puzzle using you SSTS technique?
Were you previously a maths teacher?

singaporeshortstories.blogspot.com said...

Thanks Mr Tan!

I love Sudoku but could hardly time to play it cos in Singapore, everyone is busy :(

A Singaporean said...

Oops I realized that I made myself sound like very expert when I am not really one. Anyway I tried the first one and it took me about 40 minutes to solve. Techniques I used are singles, box-line intersection removal, naked subsets, and XY-wing. My terminology generally follow those listed at http://www.sudopedia.org/wiki/Solving_Technique .

As for saying that the puzzles can be solved using SSTS, I simply ran the puzzles through one of the many sudoku solver programs out there. Two good programs are SudoCue (http://www.sudocue.net/download.php) and Sudoku Explainer (http://diuf.unifr.ch/people/juillera/Sudoku/Sudoku.html). And oh, I never invent the SSTS techniques so please don't call them mine. These are the techniques implemented in the Simple Sudoku solver program (http://angusj.com/sudoku/). To be frank, I am actually more interested in writing my own solver program like the above-mentioned rather than solving sudoku puzzles manually, except that the user interface of my program is quite lousy and I have not implemented as many techniques as the better ones.

Since we are at this topic, I might as well point you to the Sudoku Players' Forums (http://www.sudoku.com/boards/). This is where many of the newest and most advanced solving techniques get discovered.

By the way, I am not a maths teacher. Sorry to disappoint. =)

Tan Kin Lian said...

Hi A Singaporean

Can you send an email to me at kinlian@gmail.com.

We can discuss how to develop the Sudoku puzzles. I will share with you about the techniques used in my computer program to solve the puzzles and, more difficult, to generate the puzzles.

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