Q: How do we use constraint propagation to solve the naked twins problem?
A: The naked twins problem is as follows: If two boxes inside a unit both have the same two possible values, all the other boxes inside that unit cannot have these two values.

This allows us to remove additional possible values from the problem and reduce the search space.

This constraint is propagated on every puzzle reduce step to all the units, similar to the elimination and only choice constraint.

Q: How do we use constraint propagation to solve the diagonal sudoku problem?
A: A diagonal sudoku introduces two new units to the puzzle: both diagonals.

We can now use the same constraint propagation techniques on the diagonals as we did on the rows, columns and boxes.

So on each puzzle reduce step, we will also run the elimination, only choice and naked twins steps on the diagonals.

This project requires Python 3.

We recommend students install Anaconda, a pre-packaged Python distribution that contains all of the necessary libraries and software for this project. Please try using the environment we provided in the Anaconda lesson of the Nanodegree.

Optionally, you can also install pygame if you want to see your visualization. If you've followed our instructions for setting up our conda environment, you should be all set.

If not, please see how to download pygame here.

• solutions.py - You'll fill this in as part of your solution.
• solution_test.py - Do not modify this. You can test your solution by running python solution_test.py.
• PySudoku.py - Do not modify this. This is code for visualizing your solution.
• visualize.py - Do not modify this. This is code for visualizing your solution.

To visualize your solution, please only assign values to the values_dict using the assign_values function provided in solution.py

The data consists of a text file of diagonal sudokus for you to solve.