Let’s begin with focusing on the Sudoku rules. Traditionally, the Sudoku grid has a size of 9x9. In this case, the rules are formulated as follows. Every row must contain the numbers 1, 2, 3, 4, 5, 6, 7, 8, and 9. There may not be any duplicate numbers in the rows. Every column must contain the numbers one to nine only once. Every 3x3 region must also contain the numbers one to nine only once. Some numbers are predefined. Solver must find all other numbers to solve a puzzle. You can see a classic Sudoku puzzle example below.

We can also have other sizes of Sudoku field, for example 4x4, 6x6, 12x12 and 16x16. For all these puzzle sizes, the rules are identical.