Look over all cells in a row, column or box. If you find a number which only exist in one cell, this number must be the solution for the cell. Here is a sudoku (which is solved as much as possible with
IG and
SiSo).
| 3 |
1 |
|
|
6 |
|
|
2 |
8 |
| 4 |
2 |
|
|
|
|
|
6 |
|
| 8 |
6 |
5 |
|
|
9 |
4 |
7 |
|
| |
|
6 |
|
|
7 |
|
|
|
| 9 |
7 |
|
|
4 |
|
|
8 |
6 |
| |
|
|
3 |
|
|
7 |
|
|
| |
9 |
8 |
7 |
|
|
6 |
3 |
4 |
| |
3 |
|
|
|
|
8 |
5 |
7 |
| 7 |
5 |
4 |
6 |
8 |
3 |
2 |
1 |
9 |
Here is the solution table this far. Notice the number 7 i R1C3. This is the only 7 in the whole R1. This means R1C3 must be 7.
| 3 |
1 |
79 |
45 |
6 |
45 |
59 |
2 |
8 |
| 4 |
2 |
79 |
158 |
1357 |
158 |
1359 |
6 |
135 |
| 8 |
6 |
5 |
12 |
123 |
9 |
4 |
7 |
13 |
| 125 |
48 |
6 |
12589 |
1259 |
7 |
1359 |
49 |
1235 |
| 9 |
7 |
123 |
125 |
4 |
125 |
135 |
8 |
6 |
| 125 |
48 |
12 |
3 |
1259 |
12568 |
7 |
49 |
125 |
| 12 |
9 |
8 |
7 |
125 |
125 |
6 |
3 |
4 |
| 126 |
3 |
12 |
1249 |
129 |
124 |
8 |
5 |
7 |
| 7 |
5 |
4 |
6 |
8 |
3 |
2 |
1 |
9 |
By continue using SiSo and SC you will be able to solve this sudoku.