Sudoku

I do not find myself motivated to sit down and solve Sudoku problems, although there are suggestions that such an activity can reduce the withering of one's mental faculties. However, Ithought that was one of the purposes of U3A.

Nonetheless, the idea of writing a computer program to solve Sudoku was to me irresistable; especially so after reading somewhere that writing such a program would be very difficult. (Feel free to download my version. It is currently undefeated.)

More interesting than solving puzzles set by someone else is the question of actually setting the puzzles in the first place. The very first question that this issue raises in my mind is:

How many possible solution grids exist?
The rules and examples can be found here, courtesy of the Mail on Sunday.