The Hidden Pair technique identifies two candidates that appear together in exactly two cells within a row, column, or block. These candidates must go into those two cells, allowing you to remove all other candidates from them.
- Scan a row, column, or block: Look for two candidates that appear together in exactly two cells within the same row, column, or block.
- Verify other candidates: Check that these two cells contain additional candidates, but only the identified pair appears in both cells.
- Remove other candidates: Eliminate any extra candidates from these two cells, leaving only the hidden pair.
- Confirm placement: These two candidates must occupy the two cells, although their exact position between the cells is not yet determined.
In this puzzle, a Hidden Pair of 2 and 5 appears in row 4, columns 6 and 7. They only occur in two cells of their respective rows. This allows us to eliminate the 1, 3, and 9 candidates from those cells, leaving only the 2 and 5. You'll notice that by eliminating the 3 from row 4, column 7, you end up with a Hidden Single (3) in row 5, column 7, and the puzzle unravels from there.
This puzzle also includes techniques Naked Single and Hidden Single. Use these strategies together to master solving complex puzzles!
How to spot it
Pick a unit and find two digits that each appear in only the same two cells. Those cells may carry other candidates that you can then strip away.
When to use it
Use it when a unit looks crowded; a Hidden Pair cleans two cells down to just the pair and often unlocks further moves.
Common mistakes
- Confusing it with a Naked Pair; here the two cells still show extra candidates until you apply the technique.
- Not removing the extra candidates from the two cells, which is the entire point of the move.
Frequently asked questions
- What is a Hidden Pair in Sudoku?
- A Hidden Pair is two digits that can each only go in the same two cells of a row, column, or box. All other candidates can be removed from those two cells, leaving just the pair.
- How do you find a Hidden Pair?
- For a unit, note which cells each digit can occupy. If two digits share exactly the same two cells and appear nowhere else in the unit, those two cells form a Hidden Pair.
- What is the difference between a Hidden Pair and a Naked Pair?
- A Naked Pair already shows only the two candidates. A Hidden Pair is buried among extra candidates in the two cells; applying it removes those extras.