I blogged about

Foxtrot and Sudoku a while ago and it garnered a lot of interest. Given that, I thought folks may be interested in some difficult traditional sudoku puzzles I have come across.

The way I actually determine difficulty is from a program I wrote that solves the puzzles. The program implements a number of techniques to solve the puzzles and determines how hard it is based on the techniques that must be used and how quickly it can be solved. I hope to have the solver hosted where you can get to it soon, so stay tuned.

In any case, here is the hardest puzzle I have come across.

And another difficult one.

Give them a try!

wow. the first sure is a sticky one.

ReplyDeleteafter the usual walk through, I only have 2 boxes that I know are correct.

and they aren't helping any more.

First one solved:

ReplyDelete2 3 7 8 4 1 6 5 9

9 1 6 7 5 2 3 4 8

5 8 4 6 9 3 1 2 7

6 7 3 2 1 5 8 9 4

4 5 8 9 6 7 2 3 1

1 9 2 3 8 4 5 7 6

3 2 9 1 7 8 4 6 5

8 6 5 4 3 9 7 1 2

7 4 1 5 2 6 9 8 3

still working on the first one.

ReplyDeleteI have started to lean into algebra to solve

a1+b1..i1=45

a1+a2...a9=45

a1+b1+c1+a2+b2+c2...c3=45

substituting the 38 variables I already know.

I need some double secret strategy at this point!

I dont want to resort to guessing and backtracking.

learned a bit more about sudoku. and finally solved it. I built a spreadsheet table to use as my scratch pad. In the end they fell into place so rapidly that I missed and had to backup about 8 steps to find my error.

ReplyDeleteI will to have to revisit this one in a week and see how well I do.