Sudoku Craze May Hook You Too

Some games and puzzles have rules that are quickly learned, but still present a challenge. They become immensely popular. Free Cell, the solitaire game, is an example.

Sudoku is another.

Never heard of it? Ask someone in London, where newspapers are in a daily battle to have the best of these popular number-logic puzzles. Sudoku puzzles have already come to the pages of some U.S. newspapers.

The Ledger will begin publishing a sudoku puzzle on Monday. It will run daily, except Sunday, on one of the comics pages. More about it in a minute.

The puzzles have nothing to do with math and everything to do with numbers. They've been popular in Japan for two decades. Late last year, The Times of London became the first paper in London to publish daily sudoku. The Daily Telegraph of London started one in January.

In April, The New York Post became the first newspaper to publish them in this country.

Sudoku (Japanese for "single number") uses a grid of nine columns and nine rows. The grid is divided into nine 3-by-3 boxes. Sudoku has one rule:

The numbers 1 through 9 must be placed in each row, column, and 3-by-3 block, but can appear only once in each row, column and block.

Each puzzle has some numbers already in place. The puzzle's difficulty depends on how many are shown, and where they are located on the grid.

Puzzles range in difficulty from the "very easy" to "diabolical." Some can be solved by simply looking at where a set of identical numbers are located and then narrowing down the squares where the missing numbers must go.

Sometimes there will be only one number that can be placed in a box because none of the other eight numbers can go there. Sometimes a number will be forced into a box because boxes included in an adjacent column or row already contain that same number.

Those are the easy puzzles.

Others require some knowledge of special sudoku truisms that involve sets of pairs, or triple- and quadruple-number sets and their subsets. Those truisms have been boiled down into easy-to-learn logic statements that help puzzle solvers move to the next sudoku level.

For an excellent 11-page guide to solving sudoku -even the most diabolical of puzzles -- go to this Web site: www.sudoku.org.uk. Click on "Solving sudoku document."

It is written by Michael Mepham. The Ledger will be using his sudoku puzzles, which started in The Daily Telegraph of London. The Los Angeles Times, the first newspaper in California to publish a daily suduko, also uses Mepham's feature.

When the first sudoku appeared June 20 in the Los Angeles Times, Mepham wrote an introduction for readers that said, in part:

"Unsuspecting Californians may wonder what all the fuss is about. It's just an innocuouslooking 9-by-9 grid with some numbers scattered around it. No?

"Hah! That's what we in Britain thought only a few months ago before we began forgetting to pick up the kids from school, missing our train stops and clearing the breakfast table at 9 p.m. Perhaps I should warn you now? Yes, readers of the LA Times look away now . . . turn away from the sudoku grid . . . don't look . . . put that pencil down . . .

"Was I too late?"

Mepham, who now has more than a dozen books of sudoku puzzles on the market in English and is working on several foreign-language versions, told reporters that Britons haven't "seen anything (spread in popularity) like this since crosswords were introduced in the U.K. in 1925, when they were imported from America."

His puzzle rankings -- white, the easies; brown; and black belt, the hardest -- appear with each sudoku. Easier puzzles appear on Monday and grow more difficult through Saturday. The solution to the previous puzzle will appear with the next sudoku.

When solving a sudoku puzzle, it's helpful to pencil in small numbers in each square to indicate what "candidates" could wind up there. Sometimes, only one number can be placed in a square, and writing it in will solve other squares by eliminating that number from other squares.

Also published with this column are some helpful logic methods to get solvers started. Usually, many sudoku puzzles can be solved by using only the first two or three rules. Another source for a detailed lesson in how to solve sudoku puzzles can be found at: www.paulspages.co.uk/sudoku/ howtosolve/.

So pick up a sharp pencil that has a good eraser.

And don't say you weren't warned.

SOLVING TIPS