On a mid-October Monday, shortly before 9 a.m., 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. The annual championship event comprises two days of Sudoku, followed by three days of other types of pencil-and-paper logic puzzles. Although puzzlers qualify for the event on a national level, most attend just for fun and for the community — to revel with people who share in the same nerdy delight. The top solvers are also 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 Ph.D. in the School of Mathematics.