is a logic-based puzzle.
It is a type of constraint satisfaction problem, where the solver is given a finite number of objects (the numerals 1-9) and a set of conditions stating how the objects must be placed in relation to one another.
The puzzle consists of a 9×9 grid further divided into nine ×3 sub-grids (also called boxes, blocks, regions, or sub-squares).
The objective is to place the digits within the grid so that each column, row, and sub-grid contains all of the digits from to 9. Each puzzle is published with some of the boxes already filled in, and those constraints help define the problem's difficulty level.
People sometimes say there is no math required to solve Sudoku.
What they really mean is, there is no arithmetic involved in Sudoku. Mathematical thinking in the forms of deductive reasoning and algorithms are the basic tools for solving Sudoku puzzles.
Two offline game versions available