Sudoku is a puzzle based on a small number of very simple rules:
Every square has to contain a single numberOnly the numbers from 1 through to 9 can be usedEach 3?3 box can only contain each number from 1 to 9 onceEach vertical column can only contain each number from 1 to 9 onceEach horizontal row can only contain each number from 1 to 9 onceOnce the puzzle is solved, this means that every row, column, and 3?3 box will contain every number from 1 to 9 exactly once.