Last Digit




The Last Digit technique is the easiest of all techniques.

A Last Digit is a single (a solution) that results from all other cells in that region (row, column or box) being already taken by other numbers.

This technique is a very special case of the Naked Single technique, where we don't necessarily just look at one region at a time, but at all three involved regions simultaneously.

Since each row must have each digit exactly once, and since digits 1-8 are already in that row, we know that the last digit must be 9.

This, of course, also works with columns.

Here, 5 is the only digit that's missing in that column, so it goes in the empty cell.

In this 3x3 box, only a 2 is missing. It can be inserted into the only empty cell.