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Pointing Triple

Pointing TripleSTEP 0/3

Introduction

The Pointing Triple strategy applies when a specific candidate within a 3×3 box can appear in only three cells that lie in the same row or column.

If all possible positions for a given digit within the box are located in one row, we know that the digit must be placed somewhere in that row.
This allows us to remove this candidate from the remaining cells in that row, but outside the box being considered.

This is an extension of the Pointing Pair idea - this time, instead of two cells, we have three cells pointing in the same direction.

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Pointing TripleSTEP 1/3

Finding the Triple

Look at the middle 3×3 box. Let's analyze the positions of candidate 7 within it.

In Row 5, Column 4, candidate 7 is possible.
In Row 5, Column 5, candidate 7 is also possible.
In Row 5, Column 6, we find the third and final possible position for 7 in this box.

Candidate 7 therefore appears in exactly three cells within this box, and all three are located in Row 5.

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Pointing TripleSTEP 2/3

Finding the Relationship

This is the key piece of information. Since all possible positions for 7 in this box are located in Row 5, the 7 must go into one of these three cells.

The cells Row 5, Column 4, Row 5, Column 5, and Row 5, Column 6 contain all possible positions for 7 in this box.
No other cell in the middle box can contain 7.

This means that the remaining cells in Row 5 outside this box cannot contain 7.

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Pointing TripleSTEP 3/3

Making the Elimination

Since candidate 7 is now confined to the middle box, we can remove it from the remaining cells in Row 5.

In Row 5, Column 1, we remove candidate 7.
In Row 5, Column 2, we also remove candidate 7.
We do the same in Row 5, Column 3.

This is the essence of Pointing Triple: when all possible occurrences of a digit within a box point to one row, we can remove that digit from the rest of that row outside the box.

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