What is a pointing pair in sudoku?

A pointing pair happens when a candidate within a box is restricted to two cells that both lie in the same row or column. Because that candidate must be placed in the box, and both possible cells share a line, the candidate cannot appear elsewhere on that line. You therefore eliminate it from the rest of the row or column outside the box.

What is the difference between a pointing pair and a pointing triple?

The mechanism is identical; only the count differs. A pointing pair is when a candidate in a box is confined to two cells on one line, while a pointing triple is when it is confined to three cells on one line. In both cases you eliminate that candidate from the rest of the line outside the box.

When should I look for pointing pairs?

Look for them after basic singles stall, focusing on candidates that appear only two or three times within a box. Check whether all those occurrences fall on a single row or column. This is one of the most common and productive intermediate techniques, so it is worth scanning for early in the intermediate stage.

What is the difference between pointing pairs and box-line reduction?

Both are intersection techniques on the overlap between a box and a line, but they point in opposite directions. With a pointing pair, a candidate is locked to a box first, so you eliminate it from the line outside the box. With box-line reduction, a candidate is locked to a line first, so you eliminate it from the rest of the box.

Pointing Pairs: Sudoku Technique with Examples

Pointing pairs are the workhorse of hard sudoku. They are the first technique that uses the box rule to constrain a row or column, rather than the other way around. Once you can spot them, most hard puzzles open up.

How it works

A pointing pair (or pointing triple) starts inside a single 3x3 box. Pick a digit that has not been placed yet in that box. List every cell in the box where the digit could legally go. If all those candidate cells happen to sit on the same row, the digit must land somewhere on that row inside this box.

That is the key step. The digit is restricted to the box and within the box restricted to one row. So the digit goes in that row, and it cannot go anywhere else on that row outside the box. Erase the digit from those outside cells.

The same logic works for columns. If a digit's candidate cells in a box all sit on a single column, the digit gets eliminated from the rest of that column outside the box.

The digit's candidates in the bottom-left box align on row 8. It must land there. erase it from the rest of row 8.

When to look for it

Right after pencil marks are complete. Pointing pairs need accurate candidate sets to be visible. Scan each box one digit at a time and ask: do the remaining candidate cells for this digit share a row or a column?

Pointing pairs are the single most useful technique for hard sudoku. If you are stuck on a hard or expert puzzle, this is the first technique to try.

Step-by-step example

Take a box that still has four or five empty cells. Pencil-mark every candidate.
For each unplaced digit in the box, find the cells that still hold it as a candidate.
If those cells all share one row, you have a pointing pair (two cells) or pointing triple (three).
Erase the digit from every cell in that row outside the box.
Re-scan affected cells for naked and hidden singles. Pointing pairs usually create at least one placement nearby.

Pointing pair vs box-line reduction

Pointing pairs and box-line reduction are reciprocal patterns. A pointing pair uses the box to constrain a row or column. A box-line reduction uses a row or column to constrain a box. Same rectangle, different direction. Learn both and you cover every box-line overlap.

Tips for spotting it

Scan one box at a time, one digit at a time.
If a digit has only two or three candidate cells in a box, check whether they share a row or column.
If pointing pairs are not producing eliminations, the puzzle may need a naked pair first.
After applying, re-mark the affected row or column. New singles often appear.

Common mistakes

Eliminating inside the box. The eliminations apply to the rest of the row or column outside the box.
Confusing a hidden single with a pointing pair. If the digit has only one candidate cell in the box, it is a hidden single, not a pointing pair.
Letting one stray candidate sit on a different row inside the box. The pattern requires all box candidates for the digit to be aligned.
Skipping this technique and reaching for X-wing first. Pointing pairs are simpler and usually clear the same cells.

Practise it

Hard sudoku is the natural playground for pointing pairs. Mark every candidate first, then walk through each box scanning one digit at a time. After a few sessions, you will spot the alignment in under a second. Combine with box-line reduction to cover both directions of the same idea.

Pointing Pairs