Iain Dunning Problem solver. Experiences, thoughts, and technical notes. More about me. @iaindunning Sudoku is (was?) an extremely popular number puzzle. Players are presented with a 9 by 9 grid, with some of the cells filled in with a number between 1 and 9. The goal is to complete the grid while respecting these rules: Each row of the grid must contain each of the numbers 1 to 9 exactly once. Ea