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Medium

Pointing Pairs

A Pointing Pair happens when a digit's remaining spots inside one 3×3 box all line up along a single row or column. Since the digit has to go somewhere in that box, it also has to go somewhere in that row or column — which means it can be ruled out everywhere else in that row or column, outside the box.

Why it works

A digit must appear exactly once in every box, and exactly once in every row and column. If the only cells left for it in a box happen to share one row, that row's cells outside the box can't also hold it — the box has first claim.

Worked example

Example 1: Pointing Pair (Row) — Row 2

5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9
Step 1 of 3

Look at the box

In Box 1, 7 can only go in R2C2 or R2C3.

5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9
Step 2 of 3

Both are in one line

Both cells are in Row 2, so the 7 for Box 1 has to land somewhere in Row 2.

5
3
7
6
1
9
5
3478
2478
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9
Step 3 of 3

Eliminate

That 7 is spoken for, so 7 can be crossed out of the rest of Row 2.

Example 2: Pointing Pair (Column) — Column 3

9
7
4
2
1
8
7
5
2
6
1
9
4
5
4
5
7
9
9
2
1
8
3
4
5
9
5
7
Step 1 of 3

Look at the box

In Box 1, 5 can only go in R1C3 or R2C3.

9
7
4
2
1
8
7
5
2
6
1
9
4
5
4
5
7
9
9
2
1
8
3
4
5
9
5
7
Step 2 of 3

Both are in one line

Both cells are in Column 3, so the 5 for Box 1 has to land somewhere in Column 3.

9
7
4
2
1
8
7
5
2
6
1
9
4
5
4
5
7
9
9
2
1
8
3
4
5
9
5
7
Step 3 of 3

Eliminate

The rest of Column 3 has no other 5 candidates, so nothing more is removed here.

Tips

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