1, the basic elimination method is to solve the problem by using the law that the number 1 to 9 can only appear once in each row, column and room. Basic exclusion methods can be divided into row exclusion method, column exclusion method and nine-grid exclusion method;

2. Three-chain number deletion method, called three-chain number deletion method, finds out no more than three different numbers in a column, a row or nine-grid candidate number, and then deletes these three numbers from the candidates in other grids;

3, the only solution, the number that can be added to a grid has been ruled out, then the number of this grid can only be added to the number that does not appear;

4. Block exclusion method is an improved method of basic exclusion method and one of the most commonly used methods in intuitive method. ;

5. The remainder test is a method to solve the problem. When a row or a column has a large number of nine squares, and there are two or three remaining squares, the values are added to the remaining squares for testing.