Pointing pair: Sudoku Technique Explained

Pointing pair: sudoku technique

Within a box, a number is confined to one line, so the rest of that line can't use it.

How it works

Pick a box and a number. If all the places that number can go in the box sit in the same row, then the number in that box will end up in that row, wherever it lands exactly.

Since a row holds each number only once, you can erase it from the cells of that row outside the box. The same is true for columns. With three aligned cells, the logic is identical, even though the name says pair.

Worked example

This example comes from a real puzzle in our collection, at the exact moment the technique applies.

Here is the board at that moment, with the candidates still open in each empty cell. Earlier steps may already have ruled some out.
1
59
59
2
7
3
8
6
4
8
7
2
4
1
6
35
35
9
4
6
3
5
8
9
27
1
27
9
245
45
8
3
7
6
25
1
57
3
1
6
9
2
4
8
57
6
28
78
1
5
4
9
27
3
37
49
6
39
2
5
1
347
8
235
258
58
7
4
1
235
9
6
2357
1
4579
39
6
8
2357
23457
257
In this box, the candidate only appears along one line. The cells that matter are highlighted.
1
59
59
2
7
3
8
6
4
8
7
2
4
1
6
35
35
9
4
6
3
5
8
9
27
1
27
9
245
45
8
3
7
6
25
1
57
3
1
6
9
2
4
8
57
6
28
78
1
5
4
9
27
3
37
49
6
39
2
5
1
347
8
235
258
58
7
4
1
235
9
6
2357
1
4579
39
6
8
2357
23457
257
The result: one candidate goes. 2 leaves row 8, column 2.
1
59
59
2
7
3
8
6
4
8
7
2
4
1
6
35
35
9
4
6
3
5
8
9
27
1
27
9
245
45
8
3
7
6
25
1
57
3
1
6
9
2
4
8
57
6
28
78
1
5
4
9
27
3
37
49
6
39
2
5
1
347
8
235
258
58
7
4
1
235
9
6
2357
1
4579
39
6
8
2357
23457
257

Where you'll need it

Pointing pairs are a staple of medium boards and a frequent first step in harder ones.

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Practice on a medium sudoku