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Ruby Challenges / Sudoku Validator

Hey there! We're thoughtbot, a design and development consultancy that brings your digital product ideas to life. We also love to share what we learn.

This coding exercise comes from Upcase, the online learning platform we run. It's part of the Ruby Challenges course and is just one small sample of all the great material available on Upcase, so be sure to visit and check out the rest.

Exercise Intro

Difficulty: Easy

Sudoku is a logic-based combinatorial number-placement puzzle. The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 sub-grids that compose the grid contains all of the digits from 1 to 9.

Write a command-line program that can read a file containing a Sudoku grid and validates it. The grid can be partially or completely solved. Return either a success message or a list of errors and their positions.

Instructions

To start, you'll want to clone and run the setup script for the repo

git clone [email protected]:thoughtbot-upcase-exercises/sudoku-validator.git
cd sudoku-validator
bin/setup

Sample usage:

$ ./sudoku-validator valid_complete.sudoku
  This sudoku is valid.

$ ./sudoku-validator valid_incomplete.sudoku
  This sudoku is valid, but incomplete.

$ ./sudoku-validator invalid_complete.sudoku
  This sudoku is invalid.

$ ./sudoku-validator invalid_incomplete.sudoku
  This sudoku is invalid.

A Sudoku is valid if:

  1. It has no duplicates in a row
  2. It has no duplicates in a column
  3. It has no duplicates in a sub-group (the nine smaller 3x3 grids).

Input files

The input files look like this

8 5 0 |0 0 2 |4 0 0
7 2 0 |0 0 0 |0 0 9
0 0 4 |0 0 0 |0 0 0
------+------+------
0 0 0 |1 0 7 |0 0 2
3 0 5 |0 0 0 |9 0 0
0 4 0 |0 0 0 |0 0 0
------+------+------
0 0 0 |0 8 0 |0 7 0
0 1 7 |0 0 0 |0 0 0
0 0 0 |0 3 6 |0 4 0

Important: zeros represent squares which do not have a value assigned yet. Having multiple zeroes in a row, column, or subgroup does not make the puzzle invalid.

How to know you're done

This exercise provides a set of high-level integration tests that will pass when you're done. You will very likely want to write additional unit tests to test-drive your classes.

Tips and Tricks

Featured Solution

Check out the featured solution branch to see the approach we recommend for this exercise.

Forum Discussion

If you find yourself stuck, be sure to check out the associated Upcase Forum discussion for this exercise to see what other folks have said.

Next Steps

When you've finished the exercise, head on back to the Ruby Challenges course to find the next exercise, or explore any of the other great content on Upcase.

License

sudoku-validator is Copyright © 2015-2018 thoughtbot, inc. It is free software, and may be redistributed under the terms specified in the LICENSE file.

Credits

thoughtbot

This exercise is maintained and funded by thoughtbot, inc.

The names and logos for Upcase and thoughtbot are registered trademarks of thoughtbot, inc.

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