single position strategy for solving sudoku
Basic strategies
Single position
Just like the single candidate, this technique is very simple to implement. The candidature is not absolutely necessary even if it will help to visualize the cells of single position.
The rule is as follows: When a candidate appears only one time in a line, or a column or a block, the candidate is the solution of the studied cell, even if there are other candidates in this cell.
In practice, choose a line, a column or a block and review the missing numbers. Most of the time, because of the constraints by the numbers already placed; there are only two or three possibilities to place the studied number. With a little chance, there is in ONLY one position. You can consequently register it with certainty.
The more there are cells filled in the studied zone, the more there is chance that this technique is effective. I thus recommend to you to start with the densest zones and to re-use this technique as you advance in the resolution of the Sudoku puzzle.
Example
Let us try here to discover where hides the "5" in the column in yellow.
The "5" is present in the first block, we can thus eliminate 3 from the 6 possibilities.
The same reasoning applies for the following block. There remain nothing any more but two possibilities.
The "5" cannot be in the last column since this position is already occupied in the bottom block.
There thus remains nothing any more but one possibility, the good!
List of methods
