Sudoku, is full of various techniques that can lead to the solution. One such effective strategy for solving Sudoku is the 'Hidden Single technique' which also happens to be one of the most common methods used by players around the world. Despite its simplicity, this technique is a powerful tool that can reduce the complexity of the puzzle significantly.
Understanding the 'Hidden Single'
In Sudoku, a 'hidden single' is a scenario where a number only has one eligible spot in a row, column, or box.
Spotting Hidden Singles
To find a hidden single, you have to check each number in a row, column or box. Your task is to find numbers that have exactly one empty spot. The illustration below shows this.In this puzzle, the number 2 is already in the 4th and 6th rows, meaning it can't go into those rows in block 5. For row 5, columns 4 and 6 are occupied, which leaves only the 5th row in the 5th column as the valid spot for the number 2.
Advanced Example of a Hidden Single
Lets take a look at this advanced example of a hidden single. Column 5 is highlighted and we ask ourself: 'Where can the number one go in this column?' Row 2, 4 and 7 are ruled out by the definitive givens and solutions. They are also marked in the image below. The intricate aspect of this example is the hidden pair of ones in row 5. This pair rules out that a one can be placed in column 5, row 5 as well. This leaves us with only one possible cell where 1 could go. It is column 5, row 6. The cell is highlighted in green.
Follow-up Article
Without the usage of the Snyder Notion, it would be great challenge to uncover hidden singles like shown in the advanced example. Certainly, your board would be cluttered with notes, making it difficult to find further solutions. Learn more about the Snyder Notion in our article. Minimal-Sudoku was made to use Snyder Notion, give it a couple tries, we think you will like it!
In this puzzle, the number 2 is already in the 4th and 6th rows, meaning it can't go into those rows in block 5. For row 5, columns 4 and 6 are occupied, which leaves only the 5th row in the 5th column as the valid spot for the number 2.
