The game consists of integrating digits 1-9 into a matrix.
The rules are clear and simple: All digits between 1-9 must appear in each row and column, but the same digit may not appear in the same row or column more than once.
Graphically, the Sudoku board is “divided” not only into rows and columns, but also into nine cubes, highlighted in bold (see diagram).
Each cube is composed of nine cells that should contain all nine digits. This assists in the prevention of faulty digit placement.
The Sudoku board is formed by the computer, which inserts the digits in a way that makes it easy for players to fill the empty cells and crack the brainteaser.
The key to solving Sudoku usually consists of applying the process of elimination, or, in other words, avoiding the placement of digits in a way that defies the game’s basic rules.
So go get a pencil and eraser (you’ll need them) and begin working the grey cells.
Focus on one cube (not cell), say the top left-hand one. Delete all the cube’s existing numbers (inserted by the computer) and make a list of all the numbers that do not appear, meaning all those that may potentially be inserted into the matrix.
Simultaneously, examine the three rows located in the two cubes to the right of the cube we have chosen (in this case, the top middle and right-hand cubes.)
Using the process of elimination, we make a note of the digits that do not appear in each one of the rows and those that we need to find a way to insert them.
In cases such as these the game becomes one of trial and error, as logical thinking alone is not enough.
You will have to repeatedly insert and erase numbers until the diagram is completed.