Hidden singles technique

Strategy #7 for solving Sudoku: Hidden singles technique

This is a fairly simple but very useful technique for solving Sudoku. It can be applied when solving medium or hard Sudoku puzzles using notes on the game board. 

The first thing you need to do is to place all candidates for each cell on the entire game board. If you find a cell where there is a unique candidate for the entire 3 by 3 block, it means that you can eliminate the other assumptions from this cell and put the unique candidate value into this cell.

In the example above, we have placed all possible values ​​of numbers for each cell. Pay attention to the second 3 by 3 block (highlighted in red), there is one cell with a unique number for this block. And it's the number 7 (yellow circle). Therefore, this is the only cell where the number 7 can be in this square, and we can eliminate all other candidates and write it there. 

Are you passionate about Sudoku? Try a new technique for playing Sudoku right away!