A sudoku puzzle is a logic puzzle which is solved using logic and reasoning. Though the number of squares in the grid may vary, a standard Sudoku puzzle is a 9x9 grid divided into nine 3x3 blocks in which some of the numbers are given. The object of the puzzle is to fill in the rest of the grid using only the numbers 1 through 9 so that no number repeats in any block, row or column. The difficulty is determined by how many and which numbers are given and where they are placed in the grid and can range from very easy to extremely challenging.