Difficult Sudoku

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.

7 9 1     8	1 7	4 8   2
6 7	5 9   7 3	7 6
2   8 6	9 5	6     1 2 9

And another difficult one.

4   5       2 1	2	2   9         7 3
7 3         4	1   9       5   2	5         1 3
7 8         9   1	7	6 5       7   4

Give them a try!