"Obvious Singles" Technique

What is the "Obvious Singles" Strategy?

This strategy is based on the correct placement of Notes (also known as pencil marks or candidates). This technique is sometimes also called "Naked Singles".

The point is that in a specific cell, after eliminating all other possibilities, only one digit (from the Notes) remains possible. This is the payoff for all your hard work in scanning the board!

How to Find an Obvious Single

Let's have a look at this case with an example.

Pay attention to the highlighted cell at R3,C4 (Row 3, Column 4). We can see that after some solving, it is filled with only one Note.

Step-by-Step Analysis

1. Check the Notes: We look at the highlighted cell. All other notes (candidates) have been eliminated from this cell through other solving techniques.
2. Identify the Single Note: The only note remaining in this cell is the number 2.
3. Find the Solution: This means that this cell has only one possible solution. Since it is the only possible option, this cell must be 2.

The Final Step

The next move is simple: remove the Note from this cell and fill it with the final number 2.

Master This Technique

That is how the "Obvious singles" technique works. As you can see, this is not as difficult as it seems.

Therefore, if you put the "Obvious singles" technique into practice, the process of solving Sudoku will become easier and faster!