This is the official page of the free program Sudaku. It is a simple Perl script, and I am not a Perl expert, so don't expect much from it.
Since Sudaku is free software, you can download, use, modify and redistribute it to your heart's content, with some caveats (see license). If you would like to share your corrections/additions with me, I'd gladly hear of them by e-mail.
Basically Sudaku takes a
filename as argument, expecting it to contain the initial configuration of a sudoku, and outputs the solution. Yes, there are other, possibly better ("possibly" seems superfluous here), computer programs that solve sudokus, too. Now, if we are going to get nasty, I don't like your hairdress either, so we are even.
It solves the sudokus by employing a derivation of a brute-force method called backtracking. Basically, it tries succesive combinations, aborting the ones that are illegal, according to the sudoku rules. When it assigns a legal value to the last cell, it deems the combination so far the solution (it would only find one of the many solutions, when many are possible).
I planned to implement a logical method, which acted using "clever" rules. This will never come, I think.