Advanced
Hidden Pairs
A core Sudoku solving technique for advanced players
What are Hidden Pairs?
A Hidden Pair occurs when exactly two cells in a unit share two candidates that appear nowhere else in that unit - But those cells also have other candidates that obscure the pair. Because those two digits can only go in those two cells, all other candidates in those two cells can be safely removed.
This is the mirror of Obvious Pairs: instead of cells showing only two candidates, you find two digits that are restricted to only two cells.
Step-by-step guide
- Fill in full candidate notes.
- Pick a unit. For each digit not yet placed, count how many cells in the unit contain that digit as a candidate.
- Find two digits that each appear as a candidate in exactly the same two cells.
- Those two cells form a Hidden Pair - The two digits are locked there.
- Remove all other candidates from those two cells (keeping only the pair digits).
- The pair has now become an Obvious Pair - Apply standard pair elimination.
Detection guide: Hidden vs Naked
| What you look at | Naked (Obvious) Pair | Hidden Pair |
|---|---|---|
| Starting scan | Cells - Find cells with only 2 candidates | Digits - Find digits that appear in only 2 cells |
| How they look | Two cells each show exactly {X, Y} | Two cells show {X, Y, …} but X and Y appear nowhere else |
| Action | Remove X and Y from other cells in unit | Remove all non-pair candidates from the two cells |
| Difficulty to spot | Moderate | Hard - Requires per-digit frequency counting |
Pro tip: Use our Notes mode to count how many times each digit appears in a unit. Any digit appearing in exactly two cells is a candidate for a Hidden Single or Hidden Pair. Digits appearing in three cells may form Hidden Triples.