Sudoku is a game played on a 9x9 board, subdivided into 3x3 grids. Each 3x3 grid must contain the numbers 1 through 9, no repeats. In addition, each row and column must also contain the numbers 1-9, no repeats.

By deduction and logic, fill in the missing squares. Some numbers are already filled in, like this:

In the puzzle above, for example, the center square must be a “4”, since there is a “4” already in the columns on the other blank squares in the middle 3x3 grid, and each 3x3 grid must contain exactly one “4”.

Usually, the numbers are tracked by using “pencil marks,” small numbers in each square showing the possible values for each square. As the board gets filled in, the possibilities in each square are lessened.

Resources

• Sudoku Slam - An online version that can fill in candidates automatically as you learn the game.
• Solving Sudoku - Good introduction with some simple strategies
• Advanced Sudoku Strategies