DJ Ape .Net – The Home of Perfect Sudoku

First of all, I posted a Killer X puzzle rated THINKER for today. I would like to know how difficult you find this one.

Regarding the INSANE puzzle posted on Friday – I see that there has been a lot of discussion regarding it’s difficulty and the difficulty of some other puzzles posted last week. At the moment I’m rating puzzles depending on the number of different solving techniques that must be used, their relative difficulty (cage splitting is rated most difficult) and the number of times you must use each technique to solve the puzzle. For instance, the EASY puzzle posted on October 27 required only “innies/outies” and basic classic Sudoku techniques. Now, some “innies” are sometimes difficult to spot at a first glance, but it’s a basic technique which experienced solvers should’ve mastered by now. On the other hand, in addition to “innies/outies” the INSANE required cage splitting and some advanced Sudoku techniques (match/hidden subsets). I will have another look at rating puzzle difficulties and see if I can improve it. Perhaps I should rate “cage sums” more difficult for big cages (applying different combinations of possible cage sums).

Whatever the difficulty, I hope you are enjoying solving the puzzles. Difficulty is a somewhat personal issue – it depends a lot on which techniques you’ve mastered and which ones you’re still learning.

We’re still doing fine on the Top 50 Sudoku list. And we’re still the only site there posting daily Killer Sudokus (a couple of sites that claim they have Killers are actually just linking to us).

Samurai X for Saturday, October 29 – this is the only place you can find these kind of Sudoku puzzles!

Basically, not only do you have to fight against 5 interconnected Sudokus, but you also need to be carefull about the diagonals: ALL diagonals in the puzzle must contain one occurrence of each 1-9 digit. The diagonals are marked in the puzzle so you wouldn’t forget about them.

By clicking on this thumbnail a download will start which will give you the full puzzle.

Click here to download the solution

As promised, I just posted a puzzle with the rating that is currently in the lead in our poll. And that, apparently, is INSANE. This puzzle requires all Killer techniques + it requires some advanced classic Sudoku techniques (match subsets etc). It does not require trial and error! I hope someone will solve it without the aid of a computer. To be honest, I don’t plan to post many puzzles with this difficulty – it’s dangerous for your mental health!

I am surprised that according to the comments, people thought that yesterday’s puzzle wasn’t easy – all it requires for solving are innies/outies and nothing else. Although, if you haven’t practiced your outies you might find it more difficult. For instance, look at the first two rows. The sum of all cells in them must be 90. But the cage that belongs to nonet number 1 and is marked with 8 contains an outie for the first two rows! So you add up all the cages from the first two rows, find that their sum is 96 and therefore find that R3C3 must be 96-90 = 6.

There are 8 (but they solve 10 cells) innies/outies in yesterday’s puzzle altogether. If you don’t find all of them – you can’t solve the puzzle.

I also posted a 4×4 Classic Sudoku for the weekend. Don’t forget about tomorrow’s Saturday extra special – Samurai X – the only place on earth you can find them!

I realised that I’ve never posted an “Easy” Killer puzzle. So, in preparation for the weekend I just uploaded a new puzzle, rated Easy. By the way, which ever “difficulty” is in the lead tomorrow – I will post a puzzle with that rating. It look like it’s either going to be “IQ” or “Insane”.

Enjoy!

I saw two comments (by Graham and David) for the puzzle posted on October 25, and I think there’s a little clarification on “complext innies/outies” that should be made here.

You should look for innies/outies in more than just one row/column/nonet. This is a good example of such puzzle. See this image:

The cell outlined in red is the only cell sticking out of all cages that belong to the first 5 columns. So it’s value must be:
(Sum of All Cages in First 5 Columns) – 5*45.
In this case it equates to:
(4+9+15+28+10+17+21+12+14+7+24+11+12+21+14+13)-5*45 = 232 – 225 = 7.

Of course you could’ve done it the other way – as an innie of the last 4 columns.

And remember – whenever you find an innie/outie in a symetrical puzzle, there’s always one more – exactly opposite to the one you just found. I hope you see which one I’m talking about. It’s a coincidence that in this puzzle the value of the opposite innie/outie is identical (it’s also 7).

Once you solve those two and solve the two cells in the upper left corner, there’s nothing fancy about yesterday’s puzzle .

I must let you know that I’ve been working on improving the part of my software that determines the difficulty of a puzzle. Therefore, for the puzzle that I will post in a few moments, if you try to open it in “Perfect Sudoku” software, you will get a different rating from what’s indicated in the puzzle. So don’t be confused about it.

By the way, I am really surprised by the current results of the poll. I was really under the impression that the puzzles I’m posting are too difficult and was trying to change that – but you’re asking for even tougher ones! Insane puzzles, which are in the lead at the moment, either require trial and error (just like September 27 – but I won’t post such puzzles anymore), or require repeating combinations of Cage Splitting and naked/hidden/match subsets.

If “insane” are still in the lead on Friday – I will post one then. But no complaints!

I’m closing the Mobile phone poll. I’ve been so busy with other things so I’m not sure when will I get my head around implementing Perfect Sudoku for mobiles. Here are the results:

Anyhow, here is the new poll – choose your preferred level of difficulty for our Killer puzzles. It will affect which puzzles we post!

It is my pleasure to announce that we have partnered with Via Optima publishing house from Portugal and that they will be printing a book with Perfect Killer Sudoku puzzles! The book should be available in bookstores around mid November. At the moment, it will be published only in Portugal.

We are looking for publishers in other countries too. If you refer us to a publisher and they eventually print our book, we’ll surely reward you with a free copy of the book. All proposals please send to sudoku@djape.net