Getting Into Su Doku

I've been getting into Su Doku quizzes lately.

It's a 9x9 grid, made up of 3 3x3 grids. The idea behind the game is each 3x3 has to have the numbers 1 to 9 in it once only. The twist is the lines in the 9x9 must also have 1 to 9 in once only.

It's lots of fun and it's also a good mental workout.