Locked Candidates: Pointing
Pointing Pair/Triple · Locked Candidates Type 1
In a box, digit d lies on a single row (or column), so d is removed from the rest of that row (column).
Rule
Box B has d only on row R → remove d from row R outside box B.
A digit locked in a box
No cell can be filled directly any more. Look at digit 5 in box 2: it can only go in r1c4 and r2c4 — all of them in column 4. Every other empty cell is blocked by the 5 at r3c3 and r4c5 (circled).
The idea
Every box must contain one d. If all the possible places for d inside the box lie on the same row, we don't yet know which cell it is, but we do know it is on that row, inside the box.
That row can hold only one d — and it has already been reserved inside the box. So no other cell of the row, outside the box, can be d. The candidates in the box "point" along the row and clear d on the way.
How to spot it
- When scanning for hidden singles in a box leaves 2–3 cells, check whether they line up.
- It often appears when a box has empty cells on only one row or one column.
Common mistakes
- Getting the direction wrong: pointing removes d along the row outside the box, and nothing inside the box.
- The candidate cells must all be on one row; two cells on two different rows do not count.
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Related techniques
References
- HoDoKuLocked Candidates Type 1 (Pointing)(opens in a new tab)
- SudokuWikiIntersection Removal(opens in a new tab)
The examples on this page are generated from random puzzles, not taken from these sources.