Samurai SuDoku, Killer Sudoku and more

It’s been a while since I last posted this kind of puzzle. You can read about these “reverse sudoku” puzzles here:
- The rules of Hitori
- How to solve Hitori

This one I’m posting now is going to be a difficult one. I hope. Some have claimed that my Hitori puzzles are not difficult. What do you think?

Hitori 15×15 for January 31, 2012.

Hitori solution

I have a favor to ask all of you folks, particularly University students among you. I get lots of visitors from .edu domains, and I suppose most of you are students (or perhaps there are some professors too?).

Anyway… .edu domains are important. Search engines value links from .edu domains more than others. Lately I’ve been trying to optimize my website for search engines.

Would those of you who have student pages (or professor pages) on their University websites post links to my Daily Killer Sudoku or Samurai Sudoku pages? That would mean a world to me!

Something like this would suffice (copy&paste onto your student webpage)

Samurai Sudoku

<a href="http://www.djape.net/sudoku/wp/samurai-sudoku/">Samurai Sudoku</a>


Killer Sudoku

<a href="http://www.djape.net/sudoku/wp/daily-killer/">Killer Sudoku</a>


Of course anyone else with a website is more than welcome to put these links to my website.

Thanks so much in advance folks! You can post a link back as a comment here if you like

A short answer to that question would be: because I enjoy doing it! … but here is a long version, too.

Back in the summer of 2005 I realized that it’s about time I had my own website. At that point I had been computer programming for years and it kinda made sense that I should have a piece of the www for myself. So I bought the domain djape.net. Why that one? Well, because .com was already taken (and still is and it’s still “under construction”!!!). Djape is popular among people with my first name. Oh, and why Djape? Well, because that’s my nickname. Actually, my nickname is Pedja (just like recently retired All Star Pedja Stojakovic of the Dallas Mavericks), but Djape is a common variation (it’s an anagram, the two syllables are reversed). I also thought DJ APE, no matter how stupid it sounds, would be something easy to remember for English speaking folks.
Here you can hear me pronounce my nickname.

Yes, that was my voice, recorded a few minutes ago.

Anyway… now that I had a domain, what should I put on it? Earlier in 2005 I learned about Sudoku and actually I had already started creating my own software for solving and generating Sudoku puzzles. I thought, this could be interesting to other people, so I decided to put it on my website. Now, I’m a software developer, not a web-designer, so I installed a WordPress blog and started “blogging” about Sudoku.

At that time a number of Sudoku websites already existed and I realized that I had to offer something different. I added Diagonal Sudoku and Sudoku of different sizes (4×4 or 16×16 etc) first. However, in early September 2005, while surfing around, I stumbled upon The Times of London website and learned about Killer Sudoku. It immediately impressed me as a cool new variant of Sudoku and I immediately started working on my algorithms, first for solving Killer Sudoku and later for creating them.

It took about 10 days to implement a Killer Sudoku generator. On September 26, 2005, I started posting Daily Killer Sudoku puzzles. On September 27, the Killer puzzle I posted caused some controversy. Why? Well… at that time my Killer Sudoku generator algorithm was still far from perfect. It used trial and error to create&solve puzzles. It even had two singleton cages, something that I would NEVER publish now! Frankly, I wasn’t paying much attention to which puzzles I was posting on a daily basis, I spent most time working on the algorithm. And that one puzzle changed the course of this website. People showed interest, The Times’ puzzles were too easy, everybody wanted something more difficult. The September 27 puzzle was valid in the sense that it had a solution and it had only one solution, just like all other puzzles I ever posted.

If you click on the above link to Sep 27 puzzle, you can still access it, but don’t try to solve it. It’s almost impossible. It was the first INSANE Killer Soduko puzzle. Some visitors had made a lot of progress on it, and a guy called udosuk provided a solution to the September 27 Killer Sudoku puzzle with only minor trial and error. By the way, if udosuk is still visiting this website or if anyone has his contact, I’d like to get back in touch.

In the meanwhile, I perfected the Killer Sudoku generator and starting posting daily puzzles only of top quality. There was no more trial and error (although many visitors kept asking for INSANE Killers), every puzzle was human solvable, mostly by using variations of the Rule of 45 technique. Later I started adding a personal touch to the puzzles, by interactively designing them and only letting the computer do the hard work.

Anyhow… the Sep 27 puzzle and the people’s reaction to it, gave me incentive to keep making puzzles. The number of visitors to the website increased, I was interacting with people from all over the world from the comfort of my home (there was no Facebook back then! ) and it only made sense to continue doing it. Later that year I added overlapping Sudokus to my software (much easier implemented than Killer Sudoku) and among them, of course, Samurai Sudoku.

Eventually, publishers started contacting me. First was Via Optima from Portugal, who published my first book of Killer Sudoku puzzles. Then some lady from the UK sent an e-mail and later called me on my phone, also showing interest in publishing Killer Sudoku, but then disappeared. Finally, through a guy from another Sudoku website, I got in touch with the editors of The Washington Express who wanted Samurai Sudokus in their paper. They started printing Samurais in December 2005. Shortly afterwards, The Washington Post followed suit and in January 2006 published my first Samurai Sudoko puzzle.

Later a publisher from Finland asked me if I could made Hanjie puzzles for them. And I did. These are, of course, hand-made puzzles, only checked for validity by my software.

Other publishers followed. I started self-publishing books on Amazon. This was an important step and I am really happy to read your reviews of my books. Please, if you buy my books, please review them on Amazon, it means so much to me.

There’s more history, but even this is more than just a “brief” version, so I’ll leave the rest for some other time.

I make puzzles and puzzle books because it’s my passion. I do it all by myself, even the book covers! That’s why they look so childish (except for a few which were done by a friend who is a designer). Most of all I enjoy programming new types of puzzles into my software and communicating about new puzzles and my books with people who buy them and solve them. This is why I engage so much in social networks. Your reaction is important to me and it does influence my decision. Add me on Facebook, Twitter or Google+. And share with your friends!

When I publish the puzzles, I either interactively create them using my software, or generate them automatically and then hand pick them, verify the solving paths and check the difficulty. Most puzzles by other authors are too easy. I know, that because I create difficult puzzles the target audience is smaller; but I believe that the joy of having solved a difficult puzzle is much much bigger than solving a trivial one. Hence, my joy as the author also grows! I prefer to create puzzles that will get a review like this one.

This must be the longest post ever on this website. It was intended as a “brief history” but it turned out much longer than I anticipated. Oh well… I felt like writing it. Hope it wasn’t too boring!

Hi folks! Santa on this website wasn’t very nice to you, was he? Sorry for that… I will talk to him and make sure that as of Thursday, January 5, 2012 you start getting the daily Killer Sudoku, daily Sudoku variants and bi-weekly Samurai Sudoku puzzles again.

Happy New Year and best wishes!

Djape

Long time ago, some 5 years or so, I closed down the comments on the daily killer sudoku page and the samurai sudoku page. Why I did that? Because there were too many comments and the pages were loading very slowly. This was probably the worst and most stupid thing I’ve done with this website, because it immediately destroyed the ranking of this website on major search engines (apparently they love comments). But at that time, I didn’t care for that.

Well… a few minutes ago I reopened the comments on those two pages. No, I didn’t copy the old comments; we start from zero again. The old comments are available here: (warning: it takes a while to load!)old comments on Killer and Samurai Soduko.

So: feel free to comment on the daily Killer Suduko page and the Bi-weekly Samurai Sudoko page too. In fact, I would appreciate if you posted your comments there!