Sudoku Flow
Sudoku technique lessons / Hidden Single
Lesson 4

Hidden Single

The rule

If a number is a candidate in only one cell of a row, column, or box, it must go there even if that cell has other candidates.

Step by step

  1. The number 1 is missing from this row. Let's see where it can go.
  2. The other empty cells in this row are each blocked from taking 1, so remove the candidate 1 from them.
  3. Now only one cell in this row still has the candidate 1, so it must go here.
Read the full lesson, with more examples →Watch on YouTube

Try it on more boards

Each board is a real puzzle from our app, at a moment where Hidden Single applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.

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Want more boards like this?

We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number.

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Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.