Sudoku is a mathematical puzzle game originated in Switzerland at the end of the 18th century, developed in the United States and carried forward in Japan. The puzzle is a nine palace grid, and each grid is subdivided into a Jiugong grid. In each small Jiugong grid, fill in the numbers from 1 to 9 respectively, so that the numbers in each column and row of the whole big Jiugong grid are not repeated.

Sudoku game comprehensively tests the problem makers' observation ability and reasoning ability. Although the playing method is simple, the number arrangement is ever-changing. Therefore, many educators believe that Sudoku is an excellent way to train the mind. There are many factors that affect the difficulty of Sudoku. As far as the topic itself is concerned, it includes the most difficult skills, the number of times various skills are used, whether there is a combination of hidden and hidden depth and breadth, the number that can be logically deduced from the current disk, and so on. For players, the number of skills, proficiency and observation naturally also affect the difficulty judgment of a problem.

Source: @prashanttherapper