There are two main techniques one can use to solve a Sudoku puzzle; Crosshatching and Penciling In. These two techniques are simple, straightforward, reliable, and sufficient in solving most standard Sudoku puzzles.

It is important to understand that all Sudoku puzzles require an iterative approach. Except for in the case of the most simple puzzles, players will have to visit each nonet more than one time. Fortunately, each successive application of the solution techniques yields more completed cells.

Crosshatching

To begin with we will want to use the Crosshatching technique. With this technique, a player considers a single nonet (a single 3×3 square) and attempts to fill in empty cells based on the fact that a number can only appear once in any row or column. By looking across each row and down each column, we can determine if a number can or cannot go in a cell. Let’s look at an example to help illustrate the Crosshatching technique.