sudokUI › Sudoku techniques › Locked Candidates (Pointing)
Locked Candidates (Pointing) in sudoku
1-fish: box onto line · how it fits
Within one box, every candidate for a digit X lies in the same row or the same column, in two or three cells.
Why it works
The box must contain X, and every place for it is in one row or column, so the X of that row or column must lie inside the box. X is eliminated from the cells of that row or column outside the box.
How to spot it
Go through a box digit by digit: when a digit's candidates all share a row or column, follow that row or column beyond the box.
Worked example
Locked Candidates (Pointing): in box 4, digit 3 is confined to r5c1, r5c3, so it can be removed from the rest of the row. So 3 is removed from r5c4.
Practise it on a real puzzle. sudokUI generates a puzzle that needs Locked Candidates (Pointing) and takes you straight to the position where it applies. Hints draw the pattern on the board and explain the step.
Practice Locked Candidates (Pointing)Open in the app's guide
In a puzzle's rating
Each time the solver needs Locked Candidates (Pointing), the puzzle's difficulty rating grows by 50. Its class is Medium. It is needed in 34% of puzzles that sudokUI generates. How the rating works.