You may have noticed a change in your local newspaper on the funny pages, or the puzzle pages recently. Alongside the venerable crossword puzzle, the oh-so-witty jumble, and the cryptoquote, little 9×9 grids partially filled with digits from 1 to 9 have started to pop up all over. It’s called sudoku, and it’s doing for puzzles what TV dinners did for fine dining at home.
You’ve probably noticed the kudzu-like proliferation of books with sudoku puzzles at your local mega-chain bookstore. On a trip to Scotland this summer, I noticed sudoku books all over the place; the puzzle first gained popularity in Japan, then Great Britain, and finally, like some horrific avian bird flu, made its way across the Atlantic to our fair shores (apologies to KB readers not in North America).
What is sudoku? It’s a version of the mathematical oddity known as the latin square. In its classical form, it consists of a 9×9 grid, which is further subdivided into 9 3×3 grids (picture a tic-tac-toe board with a tic-tac-toe board in each square, and you’ve got the picture). The object of the puzzle is to fill the grid with the digits 1-9 (although any symbol will do — there’s nothing special about using digits) such that every row, every column, and every 3×3 box contains each digit exactly once.
The puzzles come with some of the numbers filled in already, and although it is possible to construct puzzles with more than one solution, in general, the initial numbers are such that there is a unique solution that satisfies the constraints.
So why do I dislike sudoku so much? I’ll admit that when I first started playing them over the summer, I spent a week or so in which my spare time was consumed by the challenge of trying to fill the grid. After a week, however, I had figured them out. My approach to the puzzles became entirely mechanical. There were no new challenges; only the same challenge over and over. Sure, some puzzles were more difficult than others, and I gave up on more than one. But I felt like sudoku were more or less a solved problem.
Of course, I don’t claim to be able to have a system to solve all sudoku The good folks at Wikipedia claim that sudoku is an NP-complete problem. Still, any computer science undergrad can write a simple program to do a brute force search to solve the puzzle. It may not be able to solve every problem in a reasonable amount of time, but with a little effort, most programmers could write a solver that handles a good fraction of the puzzles.
Now, crossword puzzles — there’s a puzzle for you. For one thing, to solve a crossword puzzle is to engage in a battle of wits with an unseen human adversary, the crossword puzzle constructor. When you solve a sudoku puzzle, like as not, you’re solving a computer-generating problem (although there are services that provide human-generated puzzles). And while to write a computer program that solves sudoku reasonably well might get you an “A” on your artificial intelligence homework assignment, writing a computer program that solves crossword puzzles gets you a Best Paper award at major international scientific conferences (yes, it’s been done, and it got a Best Paper).
Plus, the knowledge obtained from crossword puzzles is portable. The brain power I use to solve sudoku is essentially lost. I might as well have used it playing video games. But the mental effort expended in solving a crossword puzzle can result in long-term gains in knowledge. Sure, some of it is more or less useless (did you know that an elver is a baby eel? Useful in playing “Balderdash”, and my wife got points at a baby-shower game for knowing that), but there’s a degree of cultural literacy that comes from years of doing battle with the daily crossword.
So enjoy your sudoku, but remember, it’s like candy. A little bit won’t hurt you, and can be quite enjoyable, but too much of it in your regular puzzle diet, and you’re looking for a set of false teeth and a spare tire around your brain.