Single In Row

This technique is based on the fact that every row must contain every value once.
When there is only one cell in a row that can contain a value, this value can be safely assigned to that cell.
In many occasions this technique can be used without knowing every candidate value. In the example below
number 1 can be safely assigned to the yellow cell. This is because every row must contain one cell
with the value 1. The red lines indicate the cells that cannot contain a 1 because this value
is already present in the column. The cells with a red dot cannot contain a 1 because this value
is already present in the box. Therefore, the yellow cell must be 1.

In the example on the right, you can see all the candidate values.
The highlighted cell is the only one which can contain a 3 in this column.
Therefore this cell must be a 3, since every column must contain a 3.


