Look at a row, column or box and see if you find x cells containing x numbers. Eg 3 cells [1,3], [1,5], [3,5]. These 3 cells containts the numbers 1,3,5. Therefore 1,3 and 5 must be the solution for these cells, and we can remove them from row, column or box. Here is a sudoku solved as far as possible with the other methods.
| |
5 |
|
1 |
6 |
9 |
4 |
|
|
| |
|
|
3 |
5 |
4 |
|
|
1 |
| 1 |
|
4 |
2 |
8 |
7 |
|
6 |
5 |
| 6 |
4 |
3 |
7 |
2 |
1 |
8 |
5 |
9 |
| 8 |
|
|
9 |
3 |
5 |
1 |
4 |
6 |
| 5 |
1 |
9 |
8 |
4 |
6 |
7 |
2 |
3 |
| 9 |
|
|
5 |
7 |
2 |
|
1 |
4 |
| 4 |
|
1 |
6 |
9 |
3 |
5 |
|
|
| |
|
5 |
4 |
1 |
8 |
|
|
|
here is the solution table this far. R7C2, R7C3 and R9C2 containts the numbers 3, 6 and 8. Therefore we can remove these numbers from the rest of the box. In this case we can remove 3 from R8C1.
| 237 |
5 |
278 |
1 |
6 |
9 |
4 |
378 |
278 |
| 27 |
689 |
2678 |
3 |
5 |
4 |
29 |
789 |
1 |
| 1 |
39 |
4 |
2 |
8 |
7 |
39 |
6 |
5 |
| 6 |
4 |
3 |
7 |
2 |
1 |
8 |
5 |
9 |
| 8 |
27 |
27 |
9 |
3 |
5 |
1 |
4 |
6 |
| 5 |
1 |
9 |
8 |
4 |
6 |
7 |
2 |
3 |
| 9 |
368 |
68 |
5 |
7 |
2 |
36 |
1 |
4 |
| 4 |
27 |
1 |
6 |
9 |
3 |
5 |
78 |
278 |
| 237 |
36 |
5 |
4 |
1 |
8 |
2369 |
379 |
27 |
By continue using DC on B9 you will be able to solve this sudoku using the other reducing methods.