Philly has Sudoku's number

From 32 countries around the world, they are flying into Philadelphia with strategies in their bags of tricks, pencils in their hands, and the numbers one through nine on their minds.

They are champion Sudoku players who have qualified as the best in their nations. The rest of us may play in our living rooms, on buses or trains, or anywhere at leisure; they do, too - but for keeps. For them, Sudoku is not just relaxation. It's a proving ground.

They'll be competing, about 140 players in all, Friday and Saturday at the Fifth World Sudoku Championship, sponsored by The Inquirer. The competition will be held in the Juniper Room of the Courtyard Marriott, across from City Hall. When it's over late Saturday afternoon, one nation will reign as the team champion of the world's most popular puzzle, and one person will be named as this year's best player on the globe. All this for a trophy: The prizes have no cash value, but oh, what bragging rights.

The four previous world Sudoku championships have been in Italy, the Czech Republic, India, and, last year, Slovakia, which won the team title. Jan Mrozowski of Poland took home the individual-player championship and is considered one of the favorites to watch here. And Poland is among the tougher national teams.

After The Inquirer established the national Sudoku championship in 2007 - with prize money and an assurance that the winner would sit on the U.S. team in the world finals - publisher Brian P. Tierney put in a bid for the newspaper to host the world meet.

In 2008, the World Puzzle Federation, which runs the World Sudoku Championship, accepted the bid. It had been backed by Mayor Nutter and Will Shortz, host of The Inquirer's national Sudoku championship, New York Times puzzle editor, and puzzle master of National Public Radio's Weekend Edition.

Shortz will emcee the world championship this weekend. Although the competition has no plans for onlookers other than those accompanying the teams, Shortz says that people who want to watch the finals for the individual title, beginning at 5:30 p.m. Saturday, may do so for a $20 fee.

Shortz cites what he calls "a significant difference" in this year's world contest.

"Over the past few years, we've had some puzzles that've been so hard, it was advantageous for the solver to guess along the way and to hope that the answer works out, rather than to solve the puzzle by pure logic, as you usually would. That rewards luck," he said.

"This year's puzzles have nothing like that. If you guess, it's probably going to hurt you. It's much better to solve by pure logic."

Shortz also stressed that organizers were not concerned about cheating, which tainted the national championship last year.

That contest, at the Convention Center in October, ended with a third-place winner being suspected of cheating; he eventually was stripped of his $3,000 prize after doing poorly in a retest. The player had competed in elimination rounds and may have concealed, under the hood of a sweatshirt, an electronic device that aided him.

That's unlikely to happen at the world championship, where the participants already have won rounds in their countries in order to qualify for play here - and there is no prize money involved, just pride. "We've never had a security problem at any puzzle championship other than the one last October," Shortz says, "but we are more alert now to the possibility of cheating. If anyone were to have a hood, for example, we'd be suspicious and investigate."

The object of Sudoku, which employs logic but requires no math skill other than the ability to count from one through nine, is to fill in all 81 squares in a grid divided into nine three-by-three boxes.

Each row, column, and box must contain every digit from one through nine. Between 17 and 33 squares are already filled with a number in each puzzle, and players determine what to place in the rest of the cells to complete it.

But all that's for regular Sudoku - the puzzles carried daily in most newspapers, including this one. Some Sudoku puzzles in the world contest have no numbers filled in, but include other types of hints. Some are not in grids. And some require math skills as well as logic-based strategies.

The idea of Sudoku team play may seem unusual; it's safe to assume that the estimated 170 million Americans who have worked the puzzles solve them alone.

Three members of an international team will work together to solve a Sudoku challenge - but not always. In one round, called the Weakest Link, each team member will receive a different puzzle. "When all three solve their puzzles," Shortz explains, "they'll take certain information from that, which is necessary to solve another Sudoku puzzle they'll work on. If you have two brilliant solvers and one weak solver, that weak solver will pull you down."

Team scores plus individual-competition scores will be totaled to determine the national champs.

The six-member U.S. team includes Tammy McLeod, a programmer for Google in Los Angeles, who garnered her seat and $10,000 as first-prize winner in the national championship here last fall.

Not on the U.S. team this year are two former national winners: Thomas Snyder and Wei-Hwa Huang, both Californians who have bowed out of the competition to become Sudoku puzzle constructors. Snyder has twice won the world Sudoku title.

They have constructed all but one of this year's puzzles for the championship - many of them unlike the ones most of us do, with odd shapes, alterations to the puzzle-solving rules, and other unusual aspects. Huang, who was completing the final graphics designs this week, says he and Snyder have been working on the puzzles the last several months. Snyder says that for the expert solvers, "we'll be replicating everything you've ever seen in some way, with our own little twists on it."

Nick Baxter, who oversees this world championship, says the rounds are laid out much like the decathlon in the Olympics - 10 different events challenge different skills.

"Our goal," he says, "is not necessarily to give the most difficult examples. That's really a misnomer about this type of competition. That would be no fun. We want people to do medium-to-difficult puzzles, but do them quickly. We're looking for great solvers."

Doing them quickly are key words. Take the final individual round, when the four people with the highest scores compete for the title of world's best player, late Saturday afternoon: They'll have an hour - a nice long time, right?

But in that hour, they'll have to complete 10 Sudokus.

The World Sudoku Championship, which begins competition here Friday, will feature classic Sudoku puzzles - for starters. But most of the time teams and individuals from 32 countries will be working with Sudoku puzzles that leisure-time solvers never see. The puzzles were constructed by champs Thomas Snyder and Wei-Hwa Huang.

Try your hand at any one of these and others by printing out the sample puzzles contestants have been using for practice. Answers are included. Find them at http://wpc.puzzles.com/wsc2010/downloads/WSC5-Examples.pdf

Here's a small sampling.

Killer Sudoku

Players follow Sudoku rules, but try to determine what's in each cell. All cells are blank but have dotted lines delineating regions of the board and values within them. The numbers in each cell of a particular region must add up to the different values.

0-9 Sudoku

It's a regular Sudoku grid, but instead of using the numbers 1-9, players use 0-9 - an additional number. On each line and row, and in each box, one cell contains a slash for two numbers, and that's where the additional number goes.

Thermometer Sudoku

Different regions of a regular Sudoku grid have thermometer shapes, and digits in those areas must increase from the circular bulb to the end of the thermometer.

Odd-Even-Big-Small Sudoku

Symbols outside the grid tell players whether the first two numbers along the row or column are odd, even, the smaller numbers, or the higher ones.

Just One Cell Sudoku

A regular grid has multiple solutions, but players must find the single empty cell that will contain the same digit for all solutions - and identify that number.

Musketry Sudoku

Each of five overlapping standard grids follows standard Sudoku rules.

Primrose Sudoku

Players follow regular rules, but the playing area is nine circles of "rows."

- Howard Shapiro

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