Sunday, December 17, 2006

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
91 
 8 

















  1
7  
   

















   
 48
 2 

















67 
   
   

















  5
9 7
3  

















   
   
 76

















 2 
86 
   

















   
  9
5  

















 6 
 12
9  




And another difficult one.






































4 5
   
21 

















   
 2 
   

















2 9
   
 73

















  7
3  
  4

















1 9
   
5 2

















5  
  1
3  

















78 
   
9 1

















   
 7 
   

















 65
   
7 4



Give them a try!