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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.
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.
To start, you'll want to clone and run the setup script for the repo
git clone git@github.com: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:
- It has no duplicates in a row
- It has no duplicates in a column
- It has no duplicates in a sub-group (the nine smaller 3x3 grids).
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.
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.
Check out the featured solution branch to see the approach we recommend for this exercise.
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.
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.
sudoku-validator is Copyright © 2015-2018 thoughtbot, inc. It is free software, and may be redistributed under the terms specified in the LICENSE file.
This exercise is maintained and funded by thoughtbot, inc.
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