Sudoku difficulty rating

Question

I want to build a sudoku game with a generator. I have figured out everything how to do it without the difficulty level: easy, medium, hard. My question is how many numbers should I hide depending of the difficulty level? Any ideas.

Answer 1

I'm pretty sure that the difficulty rating for a sudoku puzzle is assigned not based on the quantity of missing numbers but on the techniques required to solve the puzzle.

Take a look at this list of sudoku solving techniques. The Naked Single and Hidden Single techniques are well-known and easy for novices to complete. The harder techniques like X-Wing and Swordfish are much more difficult.

To determine the difficulty, you should write a program that iteratively solves your puzzle, each time with more techniques in its toolbox.

Answer 2

Here are some ideas. You might also be interested in this Sudoku generator.