sudoku

Number puzzle. Although there are several variants, the traditional puzzle features a nine-by-nine grid, divided into nine three-by-three subgrids. Each subgrid must contain the numbers 1 to 9 inclusive with no repetitions, as must each row and column in the larger grid. Some numbers are given as a starting point, but only one solution is possible for each puzzle. The name derives from a Japanese phrase which means ‘the digits must remain single’.