One of our visitors (Phyllis) asked about the puzzle posted on October 13. Now, this puzzle definitely doesn’t need any trial and error to be solved – in fact it’s only rated as “thinker”. However, it requires a technique that in the new version of Perfect Sudoku will be called “complex innies/outies”. It is basically the same as regular innies/outies except that you should look for a more complex “structures” than just single nonets/rows/columns.
Here is more precisely what I’m talking about. This image shows how far you should get using standard techniques:
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Have a look at the “structure” that is outlined in red. It consists of 3 nonets and therefore the sum of all numbers in it should be 3*45 = 135. And if you pay some attention you will see that there is an innie for this whole structure in the bottom left corner of nonet number 9. Therefore it’s value must be 135-(10+11+14+18+4+13+8+28+13+7) = 135-126 = 9.
From there a few more innies/outies spawn and then you should be able to solve this baby with standard sudoku techniques (namely – naked/hidden/match pairs).
Check the Solving tips section for more details on innies/outies.