Locked Candidates Type 1 (Pointing)
intermediateWhen candidates in a box point along a line
Pointing pairs/triples occur when all instances of a candidate in a box align on the same row or column.
Understanding the Concept
Also called "Box/Line Reduction" or "Pointing Pairs/Triples".
If a candidate appears only in one row (or column) within a box, it must be placed in that row within that box.
Therefore, the candidate can be eliminated from the rest of that row (or column) outside the box.
This works because the digit must appear somewhere in the box, and it's constrained to one line.
Can involve 2 candidates (pointing pair) or 3 candidates (pointing triple).
This technique bridges basic and intermediate solving.
Examples
Pointing Pair in Box 4
In box 4 (rows 3-5, cols 0-2), candidate 7 only appears in row 3 at R3C0 and R3C1. Since 7 must go in one of these cells within the box, we can eliminate 7 from all other cells in row 3 outside box 4.
Pro Tips
- •Check each candidate in each box
- •Look for candidates that align on a single row or column within the box
- •The elimination happens outside the box, along the line
- •This technique often unlocks hidden singles
