The rules of sudoku are quite simple. In a traditional sudoku puzzle (and there are variations) you are presented with a 9x9 grid of boxes, some empty, some filled with numbers in the range of 1 to 9. That gives you 9 rows, 9 columns and also 3 larger squares of 3x3 boxes.

For example:

The idea of sudoku is to completely fill the empty grid squares with numbers in such a way that the following conditions hold true:

1) Every row should contain the numbers 1 to 9 but should not repeat the numbers 1 to 9 at any point within that row.

2) Every column should contain the numbers 1 to 9 but should not repeat the numbers 1 to 9 at any point within that column.

3) Every 3x3 square should contain the numbers 1 to 9 but should not repeat the numbers 1 to 9 at any point within that square.

Again, some examples:

Correctly Filled Sudoku Grids:

Incorrectly Filled Sudoku Grids: