Hidden Triples
Short answer: a hidden triple is three shapes whose only homes in a unit are the same three cells — so those cells belong to the trio, and every other candidate in them can be erased. Like a hidden pair, it stays camouflaged among extra notes until you track where each shape can go.
What a hidden triple looks like
Work by shapes, not cells. List the shapes a unit still needs and, for each, the cells it could still occupy. When three shapes between them are confined to the same three cells — none of the three able to escape that group — those three cells are the hidden triple, whatever else is pencilled in.
The three cells are not down to three candidates on their own — they hold more. The skill is spotting that three shapes have nowhere else to go, then clearing everything else out of those three cells.
How to find a hidden triple
- Pick a unit and list what is missing. Choose a row, column or box and note the shapes it still needs.
- Map each shape to its possible cells. For every missing shape, mark which empty cells could still take it.
- Find three shapes over three cells. Look for three shapes whose possible cells sit within the same three cells — and nowhere else. That is the hidden triple.
- Strip the other candidates. Those three cells must hold the trio, so erase every other candidate from them. They now act like a naked triple for the rest of the unit.
A hidden triple reaches the same position a naked triple would — by tracking shapes rather than cells. It is the three-cell version of the hidden pair, and one of the trickier eliminations to see by eye.
Hidden triple vs naked triple
Two routes to one pattern. A naked triple shows itself in the cells — three cells whose pooled candidates are three shapes. A hidden triple hides — the same three shapes are locked to three cells, but those cells wear extra candidates you clear away. Track cells for naked, shapes for hidden.
Frequently asked questions
What is a hidden triple in sudoku?
A hidden triple is three shapes that can legally go in only the same three cells of a row, column or box. Those cells must hold the trio, so any other candidates in them can be eliminated — even though the cells looked crowded before.
Do all three shapes need to appear in all three cells?
No. Each shape just has to be confined to those three cells, and together the three shapes must cover the group. A shape can appear in only two of the three cells and still be part of the hidden triple.
Why are hidden triples hard to spot?
Because the three cells carry extra candidates that mask the pattern. You have to track where each missing shape can go across the whole unit — like a hidden pair, but with three shapes to follow at once.
What does a hidden triple achieve?
It removes candidates. After you strip the extras from the three cells, the unit is far more constrained and usually a naked single or further elimination appears.