Sudoku solver

A simple sudoku problem solver

File format

The sudoku solver accepts a file for the following format:

• Each row consists of 9 characters (+ newline)
• Each character on a row (aside from newline) must be '0'-'9' or ' ' (if value is unknown)
• There must be a total of 9 rows

For example, a file might look as follows:

 23456789
2 4567891
34 678912
456 89123
5678 1234
67891 345
789123 56
8912345 7
91234567 

or

123456789
2 456 891
3456789  
456 89123
5678 12 4
6  91 345
789123456
8 12345 7
912345678