Pointing Pairs Sudoku Technique
Pointing pairs (also called “pointing lines”) are a classic Sudoku solving technique that can help you eliminate candidates and make progress on tougher puzzles. This strategy is especially useful for intermediate players looking to improve their logical solving skills.
What is a Pointing Pair?
A pointing pair occurs when, within a 3x3 box, a candidate number appears only in one row or one column of that box. This means that the candidate must be placed in that row or column within the box, and therefore, it cannot appear in the same row or column outside of that box.
Example:
- In a box, the candidate 8 appears only in two cells, both in the same row.
- This means 8 must be placed in that row within the box.
- So, you can eliminate 8 as a candidate from the rest of that row outside the box.
How to Spot Pointing Pairs
- Scan each 3x3 box for candidate numbers that are limited to a single row or column within the box.
- Check the rest of that row or column outside the box for the same candidate.
- Eliminate the candidate from those cells outside the box.
Why Pointing Pairs Work
If a candidate is restricted to one row or column within a box, it must be placed there. Any other occurrence of that candidate in the same row or column (but outside the box) would violate Sudoku rules.
Example in Action
Suppose in the top-left box, the candidate 4 appears only in the top row of that box. You can then remove 4 as a candidate from the rest of the top row in the other two boxes.
Practice and Tips
- Use pencil marks (candidates) to spot pointing pairs more easily.
- Pointing pairs can also occur with three cells (pointing triple), but the logic is the same.
- Combine this technique with others like naked pairs and hidden singles for best results.
Summary
Pointing pairs are a simple but powerful way to eliminate candidates and make progress in Sudoku. Look for them in every puzzle to sharpen your solving skills!
Ready to practice? Try our Sudoku puzzles and put pointing pairs to use!