You said sudoku.

Sudoku is a puzzle game that originated in Switzerland at the end of 18, then developed in the United States and Japan. Sudoku is nine palaces, and each palace is divided into nine squares. Give some known numbers and problem-solving conditions in this eighty-one box, and use logic and reasoning to fill in the numbers of 1-9 in other blanks. Make every number of 1-9 appear only once in every row, column and house. This game comprehensively tests the observer's observation ability and reasoning ability. Although the game is simple, the arrangement of numbers is ever-changing, so many educators think sudoku is an excellent way to train their thinking.