http://ravimohan.blogspot.com/2007/04/learning-from-sudoku-solvers.html
I was inspired by this article to write a sudoku solver. I'm not sure if I'm smarter than Ron Jeffries, but my solver works for every puzzle I've tried. :)
Written in C, to make it more fun. No malloc.
Reads the board from a file and writes the solution to standard out. Supports two board file formats, sdk and sdm.
Cheers, Jim