A sudoku puzzle consists of a 9 x 9 square grid subdivided into nine 3 x 3 boxes. Some of the squares contain numbers. The object is to fill in the remaining squares so that every row, every column, and every 3 x 3 box contains each of the numbers from 1 to 9 exactly once. Solving a Sudoku puzzle involves pure logic. No guesswork is needed — or even desirable. Getting started involves mastering just a few simple techniques.