Sudoku burst onto the world stage in 2005 and continues to grow in popularity. Perhaps one of the secrets to its success is the puzzle's charming simplicity. Sudoku is played on a 9 × 9 grid. Heavier lines subdivide this grid into nine 3 × 3 boxes. The object is to fill in the grid so that every row, column, and 3 × 3 box contains the numbers one through nine with no repeats. The puzzle begins with some of the numbers already entered. There will always be just one solution for each puzzle.