Sudoku techniques · Hard
Hidden Triple in Sudoku
A Hidden Triple is three numbers whose candidates, across a whole row, column or box, appear only in the same three cells. Those cells are reserved for those numbers, so every other candidate in them can go, even though each cell may be carrying five or six at the time.
Why it works
Three numbers whose candidates together appear in only three cells of a row, column, or box claim those cells for themselves.
How to spot it
Build a small count for the unit: for each missing number, list the cells that could take it.
- Look for three numbers whose cell lists together touch only three cells. Not every number needs to appear in all three.
- These are genuinely hard to see by eye, which is why they mark the top of the Hard band.
- The payoff is large: three cluttered cells usually collapse to singles within a move or two.
Builds on
Worked example
These are the app's own lesson boards. Step through them the same way a hint does.
- 1
In this row, 2, 3, 8 appear as candidates only in these three cells.
- 2
These three cells must contain 2, 3, 8 among them, so we can remove any other candidates from those cells.