Sudoku is a mathematical puzzle game that originated in Switzerland at the end of the 18th century, was later developed in the United States, and was popularized in Japan. The puzzle is a square shape with nine grids (i.e. 3 grids wide and 3 grids high), and each grid is subdivided into a nine-square grid. In each small nine-square grid, fill in the numbers from 1 to 9 respectively, so that the numbers in each column and row of the entire large nine-square grid are not repeated. The gameplay logic of Sudoku is simple, and the arrangement of numbers is ever-changing. Many educators believe that Sudoku is a good way to exercise the brain.