Find the same number in two rows of three parallel nine squares, and then use nine squares to get the position of another row of numbers. This method is suitable for advanced Sudoku.

2. Patrol grid method

Find out the number that appears frequently in every nine squares and get the position of the number in the other nine squares. This method is applied after the first method.

3. Exclusion method

This method is the key to solve the problem, and it is also easy to be ignored by ordinary people. If you observe in all the ranks or nine squares, if you can't fill in any other numbers of a position, please fill in the rest.

4. undetermined method

This method is not commonly used, but it is very effective. Make sure a number is temporarily in a certain area, and then use it to eliminate it.

5. Hierarchy method

This method is used in the final stage, first breaking through the ranks to improve the efficiency of problem solving.

6. Hypothetical method

As a master, I don't advocate this method, that is, fill in a number at random in a certain position and then deduce it, which may eventually lead to contradictions and negative conclusions.

7. Frequency method

Compared with previous methods, this method can improve efficiency. List all the situations in a row or nine squares, and then choose the number with high frequency in a certain position.