This is an example of a 12x12 Sudoku. They are very similar to normal 9x9 Sudoku puzzles and you can
apply all of the same techniques. A standard 9x9 Sudoku will use the numbers 1 to 9, a 12x12 Sudoku
will also use the letters A, B and C.
Each row, column, and 3x4 region must contain 1-9, A, B, C once and only once. The letters can be
treated in exactly the same way as the numbers, we're only using letters because we ran out of numbers!