Clueless Zero Killer Sudoku

This could well be the most difficult puzzle I’ve ever created. Yet, unlike some previous ones which were intentionally created to require trial&error, this one can surely be solved without guessing.

This is a Zero Killer Sudoku puzzle in a Clueless format. Once more I want to thank Ruud for inventing the “Clueless” arrangement of puzzles.

For those who are new to the Clueless concept, I would first suggest to try and solve some earlier puzzles of this sort. Here is a link to Clueless Sudoku X and here is a link to Clueless Killer Sudoku.

Rules: There are 9 Sudoku puzzles with no overlapping regions! Solve them according to the rules of Sudoku and use the given cages as clues. Small numbers shown in each cage indicate the sum of cells that constitute that cage. Numbers cannot be repeated in a cage! If you only look at the 9 sub-puzzles, you won’t be able to solve the whole lot! Why? Because there is the 10th sub-puzzle hidden! Here is where the “clueless” part comes in: in all 9 puzzles, the center nonet is completely empty. As you plug in your numbers, center nonets (shaded in grey) start filling up. The trick is that those 9 center nonets, put together, also constitute a valid Sudoku puzzle. So, when you run out of ideas, start working on the 10th puzzle and it will give you enough information to solve the whole lot. Those 10 puzzles together have, of course, a single solution.

Clueless Zero Killer Sudoku for Thursday, August 30, 2007 – this is the only place you can find this kind of Sudoku puzzles!

(click to download or right-click to save the image)

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To see the solution to this puzzle click here
Previously I said that you should not attempt to solve these puzzles because they’re too difficult. This time I’d like to here from you what you think!

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  1. Scott Urman
    Posted August 30, 2007 at 11:35 pm | Permalink

    This looks like quite a bit of fun! I’ll post back when I manage to finish it (he says optimistically).

  2. Gaynor
    Posted September 2, 2007 at 11:16 am | Permalink

    Goodness!! Looks like I won’t be designing any more killers for a while!

  3. Peter
    Posted September 7, 2007 at 10:14 pm | Permalink

    couldn’t get through it. I got about half way but it was simply too much fine detail not to make a mistake eventually.

  4. mikejapan
    Posted September 20, 2007 at 1:16 pm | Permalink

    Having just finished all the puzzles in Djape’s Samurai killer book, I thought I’d give this puzzle a bash. I’ve spent a week on it and I have to say it’s too difficult for me.
    I’ve only placed 211 numbers, but it was a struggle for each and every number. It just didn’t flow at all.

    First I concentrated on K2, then K1, K4, K7 then got stuck.

  5. Jill
    Posted September 20, 2007 at 10:34 pm | Permalink

    The best sudoku I’ve come across. It filled my spare time for a couple weeks. Do you have any more hard ones? or know any other sources for challenging ones?

  6. olaf
    Posted September 21, 2007 at 7:24 pm | Permalink

    What a great puzzle !
    After countless hours of working on it I finally solved it – yeah !

    Can’t wait for the next one of these.

    Thanks for all these great puzzles. Keep up the good work.


  7. John Chapman
    Posted October 6, 2007 at 10:42 am | Permalink

    Excellent fun. It took me about 8 separate sessions over a couple of weeks – including not a little frustration when I made an error and had to rub out the complete bottom third of the puzzle.

    Can I have my life back now?

  8. Scott Urman
    Posted October 18, 2007 at 2:29 am | Permalink

    I finally finished, but only by cheating a few times with the answers. Definitely the hardest one yet!

  9. Pansy Burke
    Posted May 8, 2009 at 1:09 am | Permalink

    I just happenned upon this puzzle and I love the concept of it. However, where can I get a COMPLETE list of rules for solving THIS puzzle type? I have run into exceptions to the few rules that I know of…i.e.: is the “hidden puzzle” an X-Sudoku or not? All my answers so far are correct according to your given solution, but stuck now on the X question. Your soution shows tht the hidden puzzle is NOT an X-Puzzle. I am confused! Would appreciate any help on this!!

  10. Posted May 8, 2009 at 7:43 am | Permalink

    Pansy, this particular puzzle (Clueless Zero Killer 20070830) is not a diagonal (X) puzzle. Therefore, the “hidden” puzzle is also not an X.

    A complete set of rules is shown in this post. There’s nothing more to add. Just solve. 🙂

    Good luck!

  11. Pansy Burke
    Posted May 8, 2009 at 9:01 pm | Permalink

    Thanks for clarifying this for me. I will keep plugging away at this puzzle! I must have somehow made an error in solving within the big “G” nonet, as I can’t get any further with it and there is no relation with other numbers outside of “G” to help solve. My answers are as yours:

    782 645 391
    139 278 456
    456 319 728

    (candidates: 68,49,17 – 15,23,46 – 58,37,29)
    (candidates: 68,49,17 – 15,23,46 – 58,37,29)

    523 897 164
    978 452 613
    214 763 985
    365 981 247

    Thanks again!

  12. Pansy Burke
    Posted May 17, 2009 at 8:26 pm | Permalink

    Done! Done!! Done!!! Wow! What a challenge this was! Got any more like this??? Thanks for the challenge!!

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