Over the holidays my mother-in-law got my wife and me hooked on Sudoku (suh-DOE-coo), a puzzle game with a single rule:
Fill in the grid so that
» every row,
» every column, and
» every 3 x 3 box
contains the digits 1 through 9.
Here is an example of a Sudoku puzzle before and after being solved:
Apparently, Sudoku has been around for a while and began rapidly gaining in international popularity in 2005. TB and I saw puzzles in the Hemispheres in-flight magazine on our most recent United Airlines flight. Also, one of the flight attendants had one of the many paperback books full of Sudoku puzzles.
You can read more about this addictive game at the Wikipedia entry linked above and on this Sudoku software website. The software version of the game — which allows one to play an unlimited number of puzzles for four weeks before requiring registration — costs just $14.95 for unlimited puzzles with user-specified difficulty.