Japanese game of Sudoku
Lately, I've come across lots of books and articles on the Japanese game of Sudoku. Knowing nothing about it I did a little searching on the web. According to the Wikipedia:
"Sudoku, sometimes spelled Su Doku, is a logic-based placement puzzle, also known as Number Place in the United States. The aim of the canonical puzzle is to enter a numerical digit from 1 through 9 in each cell of a 9×9 grid made up of 3×3 subgrids (called "regions"), starting with various digits given in some cells (the "givens"). Each row, column, and region must contain only one instance of each numeral. Completing the puzzle requires patience and logical ability. Its grid layout is reminiscent of other newspaper puzzles like crosswords and chess problems. Although first published in 1979, Sudoku initially caught on in Japan in 1986 and attained international popularity in 2005."
There's a comprehensive site devoted to this game at: http://www.sudoku.org.uk/ , where you can play online. On the right side of the main page there's a link for the Daily Sudoku game. A prize of a Soduku puzzle book is awarded for solutions to the daily puzzle. It's interesting to see that people from every corner of the world submit entries.
These are not easy puzzles to solve. I tried one, and it certainly got my ganglia twitching.