9 thoughts on “Slightly less hard sudokus”

  1. ‘Now he has created his hardest one yet which will certainly stretch even seasoned Sudoku solvers. ‘We don’t believe the puzzle is impossible because Mr Inkala has solved it himself. ‘Can’t this be running slightly less wild?’

      1. The Inkala puzzle was possibly the world’s hardest at the time he published it. It is not now.

        The hardest puzzle now is probably the Golden Nugget, with a few others close behind.

  2. Hi Neil

    You spotted that I am doing clones! I am impressed. Personally I am not that good at sudoku. I just happened to notice that two sudokus would be the “same” if you swapped 2 rows or 2 columns within the same group of three or if you swap whole column triplets or row triplets. That means there are 6^8 = 6*6*6*6*6*6*6*6 = 1679616 clones using the same numerical labels. Then there are factorial 9 = 9! = 9*8*7*6*5*4*3*2 = 362880 ways of shuffling the labels themselves which gives 609,499,054,080 clones (609 billion) of any given puzzle. While these must all have a solution, it does not mean that they are equally easy to do, as I had first thought. I never dreamed that anyone would be able to spot clones.

    Creating clones is very easy to do in Python which has a built-in routine called “shuffle” for shuffling arrays.

    That’s it for me. It’s been fun.



    1. Hi John,

      How easy it is to spot clones varies with the complexity/hardness of the Puzzle. For easy puzzles, you may find up to about 10 different first eliminations, and as many, or more, for the next one, until completed.

      For very hard puzzles, there is usually only one first elimination – and if you don’t find that, you are stuck – unless you do a lot of guessing until you find it. After that, again, only one thing to find. And remember, in the very hard puzzles you have to use a different pattern find. The Pattern Finds have different names. If you find a puzzle with a sequence of the same names, it is likely a clone. The puzzle that I originally sent to you needs about 20 specific patterns – in strict order, before the puzzle can be completed.

      A simile… Imagine you exit the West Western Hotel in Hobart, and you want to go to Salamanca Market. You can get there by different routes and anybody else can also go by different routes.

      A more difficult journey would be to get from Tullah Lakeside Lodge, Tullah, Tasmania to Alice Springs Library. You would have limited choices to go on that route.

      Try this SE8.9 puzzle. There are 10 possible routes to find the first elimination, and not many more until the completion of the puzzle. The likelihood of people finding the same first elimination in different clones, is very unlikely.


      Best regards

      PS: By the way, ‘whole column triplets’ are usually called Stacks and for rows – Tiers.

      1. Thanks Neil. You have given me some insight into how serious sudoku players go about it. If I start to take it that seriously I won’t enjoy it any more. I do it is a sort of relaxation exercise. It looks as if finding new, hard sudoku is like mining bitcoin.

  3. Hi John,

    Thanks for these. However, I must say that I am not interested in any more, as the ones you posted are clever clones of the one that I sent to you, and not completely new ones.

    You may find more interest inthe Tough pages. One of the members on that page posts a copy of a puzzle from one of the ‘Extreme Sudoku’ sites’. Those go down quite well with the members on the Tough pages. However, I should point out that they only like sudokus with an SE rating of between 7.0 to about 9.3. If you copy one of those from a few weeks previously, and do the clever shuffle, they will probably like those.

    Best regards

    The one which you did for me is very difficult – SE 11.4. I only like puzzles abouve 11.0. Note that the most difficult I’ve seen so far is SE11.9.

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