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Artificial Intelligence Nanodegree

Introductory Project: Diagonal Sudoku Solver

Question 1 (Naked Twins)

Q: How do we use constraint propagation to solve the naked twins problem?
A: Naked twins provides constraint propagation by:

  • Find the naked twins or boxes with identical value pairs
  • The peer boxes of the identical pairs cannot contain the naked twin values
  • Eliminate the values in peer boxes
  • Increase performance calling the naked_twins method on the values dictionary by decreasing the number of possible values for a given box

Question 2 (Diagonal Sudoku)

Q: How do we use constraint propagation to solve the diagonal sudoku problem?
A: Diagonal sudoku provides constraint propogation by:

  • Diagonal units must contain values 1-9
  • Adding diagonal units to the units list adds an additional contraint to the only only_choice method


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.

Optional: Pygame

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.


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


Before submitting your solution to a reviewer, you are required to submit your project to Udacity's Project Assistant, which will provide some initial feedback.

The setup is simple. If you have not installed the client tool already, then you may do so with the command pip install udacity-pa.

To submit your code to the project assistant, run udacity submit from within the top-level directory of this project. You will be prompted for a username and password. If you login using google or facebook, visit [this link]( for alternate login instructions.

This process will create a zipfile in your top-level directory named This is the file that you should submit to the Udacity reviews system.