sudokUI › Sudoku techniques › Locked Triple
Locked Triple in sudoku
Naked Triple clearing two units · how it fits
Three empty cells in one box that also share a row or column contain between them only the candidates X, Y and Z, though no cell needs all three.
Why it works
Three cells that all see each other need three different digits, and only X, Y and Z are available, so all three are used there. X, Y and Z are eliminated from every other cell of the box and of that row or column.
How to spot it
Check the three cells where a box crosses a row or column: all must be empty and hold just three different candidates between them.
Worked example
Locked Triple: cells r8c1, r8c2, r8c3 contain only 2/3/7, removing those digits from the cells they all see. So 2 is removed from r8c8, r7c2; 7 is removed from r8c7, r8c8, r7c2, r7c3.
Practise it on a real puzzle. sudokUI generates a puzzle that needs Locked Triple and takes you straight to the position where it applies. Hints draw the pattern on the board and explain the step.
In a puzzle's rating
Each time the solver needs Locked Triple, the puzzle's difficulty rating grows by 60. Its class is Medium. It is needed in 1 in 57 puzzles that sudokUI generates. How the rating works.
More intersections
Locked Pair · Locked Candidates (Pointing) · Locked Candidates (Claiming)