Try it out: http://www.snarkpit.net/dev/sudoku/
And http://www.sudoku.com/ for those who don't know what I'm talking about.
It doesn't have any ?ber-advanced things going on (such as noticing invalid grids) but it solves the puzzle like a human would 
Its a puzzle that has to have 1 through 9 in vertical and horizontal axis- why can't it use those words instead of having some stupid explanation. It doesn't look hard, just time consuming, and I'm sure theres better ways to spend my time...
Oooooh I just noticed the spell checker!
No of course it doesn't use brute force to solve it- it tells you what it's doing if you put one in (or try a 'default' one by submitting a blank grid). It scans and fills, but it doesn't yet do contingencies ('guesswork' of sorts, ruling out options by trying them) which is needed for some of the trickier versions :/
Much easier that way than waiting for an answer too.
boolean solve (Board board, int row, int col)
{
for (int i=1; i<10; i++) //cycle through possibilities for the current cell
{
if ( board.isLegalMove(i, row, col) )
{
board.setCellContents(i, row, col);
cell c = board.nextOpenCell();
if (c == null)
return true;
if ( solve( board, c.row(), c.col() ) ) //yay recursion
return true;
}
}
board.setCellContents(0, row, col); //reset contents
return false;
}
