Sudoku solver

sudoku.txt

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

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

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

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

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