ON a mid-October Monday, shortly before 9am, 179 elite puzzlers made their way into the ballroom of a Toronto hotel and found their allocated seats for the World Sudoku and Puzzle Championships.
Valentin Miakinen of France positioned a plastic, pigeon-shaped hunting decoy at the front of his desk, for luck. Hwangrae Lee, from Korea, polished his pencil sharpener with a tissue.
Quiet descended as proctors distributed booklets for Round 1: nine Sudoku puzzles, with a 45-minute time limit. Thomas Snyder, the general manager of the event, announced: “We begin in 5, 4, 3, 2, 1 – go!”
Snyder likened that moment – when competitors hurriedly flip open their booklets – to both Christmas morning and the start of the SAT, “a mix of joy and panic,” he said.
The top solvers are there to win. (The glory comes with a trophy, but no prize money.)
For the Sudoku event, the leading contenders this year included Tantan Dai, 23, who grew up in Beijing and is pursuing a doctorate in mathematics at the Georgia Institute of Technology; and Tiit Vunk, 40, a transport engineer from Elva, Estonia, whose wife, Regina, and daughters – Elis, 16, and Iiris, 11 – joined him on the trip.
Dai and Vunk first met at the 2013 World Sudoku Championship in Beijing, and have since become best friends – they have set the collective goal of together placing first and second at these events. Last year, in the playoffs, Vunk beat Dai by a mere eight seconds (he also won in 2016).
Looking back, Dave Baines, an emerging technology researcher and chair of the hosting Canadian team (the USA team co-hosted), praised it as “good theatre”.
This year Dai came prepared to triumph; her “performance optimisation kit” included twin plushies named Cinno and Doudou, earplugs, a halogen lamp mounted on a spare water bottle and an herbal oil for acuity and calm.
The Dai-Vunk rematch was highly anticipated, yet Kota Morinishi, 34, from Tokyo, a four-time world champion who works in information technology, took an early lead, fuelled by a sack of candy ever on offer from his team captain.
Dai had a rough start: in Round 2 of 10 she made mistakes on, or “broke,” the same puzzle three times; ultimately she erased the whole thing and restarted. In Round 3, while focused on fixing two broken puzzles, she forgot a puzzle and didn’t complete it before time was up.
Vunk finished Round 3 with three minutes to spare – “Could’ve been better,” he said – putting him in first place, with Dai second.
Byron Calver, 38, a civil servant in Toronto who sat next to Dai, was not thrilled with his showing. (His best finish was fifth, in 2010, but he had practised too hard and burned himself out, he said. Now, after a hiatus, he was trying to recapture what he had lost: “Discovering your mortality by being bad at Sudoku, the Byron Calver story,” he said.)
When asked how Round 4 had gone, he said, “It did not go.” It involved Sudokus with arithmetic constraints. “I did great at the math, I just forgot how to do Sudoku,” he said.
And at least once that day, in desperation, Calver resorted to a “wild bifurcation” – “bifurcation” being Sudoku-speak for “guess.” Typically, it is a calculated trial-and-error guess, exploring one of two clear paths presented by a partially completed puzzle. But in such an either-or gambit, only one path is correct.
Calver’s bifurcation was more reckless, he said, “insofar as it was spurred more from blind hope in the absence of a clear path forward than from any well-grounded expectation that progress would result”.
At the outset of most rounds, Will Shortz, executive director of the 2023 World Sudoku and Puzzle Championships and chair of the World Puzzle Federation, a non-profit that supervises the event, stopped by the ballroom to collect the latest booklet and sometimes try a Sudoku or two. (He and Snyder underwrote the expenses for the WSPC.)
Shortz has been the crossword editor at The New York Times since 1993, and is partial to word puzzles. He has a degree in “enigmatology” – a field of his own devising, although he said that the word could be found in 18th-century dictionaries, describing the study of riddles; he broadened the definition to include puzzles of all sorts.
“We’re living in a golden age of puzzles right now,” he said before the event. “And it’s not only a golden age in interest in puzzles. It’s a golden age in invention and creativity in puzzles. I think it’s because more people use their brains now for their living than ever before.”
At the start of Day 2 of the Sudoku competition, Dai and Vunk were tied for first place. They each solve using both a pen and a pencil, when certain and when guessing. Otherwise, they have different styles and strategies.
To prepare, Vunk might solve 20 to 30 puzzles a day, 50 to 70 daily on weekends; when a competition approaches, he eases off, tapering as he would before running a race.
Dai solves intensively, say six to seven hours straight on a Saturday, to get ready for the pace of the competition. And she keeps practising throughout the event, to warm up and keep limber.
Dai and Vunk were ranked first and second heading into the playoffs, with Morinishi in third and his Japanese teammate, Ken Endo, 30, a mechanical engineer, in the fourth spot.
The competitors gathered in a room, sequestered from the audience; each had a camera trained on his or her clipboard, with live-feed video projected onto a screen in the ballroom.
Dai’s point advantage going in earned her a 16-second head start on Vunk. She maintained her lead until the 10th and final puzzle.
“Those digits are going in fast, she might be onto something,” said Snyder, commenting on her homestretch progress. Shortly thereafter, Dai erased the entirety of her nearly complete grid.
The audience gasped. She had tried a bifurcation but it hadn’t worked out. (“It didn’t contradict until the last few digits, so it seemed like I almost finished,” she said later.)
Snyder observed that Vunk seemed to be making poor choices: “He will also be in some pain soon.”
Sure enough, out came his eraser. Dai proceeded to finish first, with Vunk second, 4 1/2 minutes later, followed by Kota in third, another four minutes behind.
(Japan won the Sudoku team title, and the United States won the puzzle team title. Endo won the individual puzzle championship, by a large margin, his third win; he also won the Sudoku title in 2019. Anderson and Thomas Luo, of Team USA, placed second and third in the WPC.)
Overall, Snyder noted that the solvers’ idiosyncratic notations on the grids – memory cues and the like, beyond the basic method he used a decade ago – were “advancing the science of Sudoku,” allowing solvers to get faster and faster. — ©2023 The New York Times Company
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