Sudoku
Sudoku Pointing Pairs — Box-to-Line Elimination
4 min read · Burmly
Pointing pairs (also called box-line reduction) appear regularly in medium puzzles — often the step that breaks a stall when naked and hidden singles have run dry. They're fast to find and reliably produce new information.
The core idea
Inside a 3×3 box, look at where a digit can still be placed. If all its candidate cells fall in a single row or column within the box, eliminate that digit from the rest of that row or column outside the box.
Top-center box, looking for digit 5:
· [5] ·
· · ·
· [5] ·
Both 5-candidates are in column 5.
→ Remove 5 from all other cells in column 5.
Why it works
Digit 5 must go somewhere in this box. The only options are in column 5. One of those cells will get the 5. Either way, column 5 has its 5 accounted for from within this box — no other cell in the column can hold it.
Row-confined pointing pairs
Middle-left box, digit 7:
· · ·
[7] [7] ·
· · ·
Both candidates are in row 5.
→ Remove 7 from all other cells in row 5.
Pointing triples
Three candidates in one row or column within a box. Same logic — eliminate from the rest of that line. Less common than pairs but follows identically.
How to find them efficiently
- Pick a digit with several placements remaining
- For each unsolved box, check which rows and columns its candidates fall in
- If confined to one row or column → eliminate from the rest of that line
- Repeat for all digits
After eliminating: always rescan the affected row or column for hidden singles. Pointing pair eliminations often directly reveal a placement.
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