#Sudoku Solver

Sodokus are simple number puzzles that often appear in various sources of print. The puzzle you are given is a 9 x 9 grid of numbers and blanks, that might look something like this:

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

The task is to fill in the remaining digits (1 through 9 only) such that each row, column, and 3 x 3 box contains exactly one of each digit. Here's the solution for the above puzzle:

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

Feel free to expand on the concept outside of a simple CLI app and create a web app/ API/ whatever.

Notes

Adapted from ruby quiz #43, please do not look for solutions.

As often is the case with magic nights, this is a pure ruby problem and does not necessitate a framework such as rails. If you are a newer rubyist you may not be familiar with Ruby outside of a framework. Never fear though, magic nights are designed to improve our Ruby skills both inside and outside of frameworks. To get you started with the basics of reading a text file I will refer you to the ruby documentation for File, e.g. to read the input files for this exercise.

You can create a basic ruby script like solver.rb and then run it from the command line like:

ruby ./solver.rb

Feel free to ask questions if you need more help!