Hidden Singles - The Next Step After Naked Singles
A hidden single is a digit that only fits in one place inside a row, column, or 3x3 box, even though the target cell may still contain multiple pencil-mark candidates. In other words, the placement is hidden inside the unit, not obvious from the cell alone.
This is the technique that turns a beginner into an intermediate solver. If you are moving from Easy Sudoku toward Medium Sudoku, hidden singles are the pattern you will see most often once simple naked singles start to disappear.
Naked Singles vs Hidden Singles
With a naked single, you inspect one cell and discover only one candidate is left. With a hidden single, you inspect an entire unit and discover only one cell can take a particular digit. The cell may still look messy, but the digit itself has no other legal home.
That is why hidden singles reward structured scanning. Instead of asking, “What fits here?”, you ask, “Where can this digit still go in this row, column, or box?”
How to Find Hidden Singles
- Choose a row, column, or box.
- Pick a digit that is still missing from that unit.
- Check every empty cell in the unit and remove the positions blocked by row, column, or box conflicts.
- If only one position remains, that digit is a hidden single.
A good habit is to scan digit by digit. For example, check where 1 can go in a box, then 2, then 3. This keeps your search systematic and exposes patterns your eyes might miss in a random scan.
Box vs Row and Column Hidden Singles
Box hidden singles are usually easiest to spot because each 3x3 area is visually compact. Row and column hidden singles often appear after a few candidate eliminations or after using a technique like Naked Pairs. Good solvers bounce between all three unit types instead of treating them separately.
Frequently Asked Questions
What is a hidden single in sudoku?
A hidden single is a digit that can only go in one cell inside a row, column, or box.
How is a hidden single different from a naked single?
A naked single is obvious from one cell. A hidden single is only obvious after scanning the whole unit.
When do I need hidden singles?
You need them regularly in medium puzzles and in almost every harder puzzle too.
Next Steps
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