The Naked Pair Technique in Sudoku
Naked Pair Technique
When two cells in the same unit (row/column/block) may contain only two identical candidates:- A digit must occupy those two cells.
- Both digits must be removed from all other cells in the unit.
When two cells within the same house contain only the exact same two candidates, those numbers must occupy those two cells in some order. As a result, the same candidates can be safely removed from all other cells in that house.
Example1:
Looking at Example 1 first, candidates for cells R8C3 and R8C4 are only 3 and 9 and share the same row (Row 8). So, either R8C3 or R8C4 will be 3 and the other will be 9. We are still struggling to figure out which one refers to which. One thing that is certain is that R8C2 cannot be 3 anymore, and therefore all other candidates for Row 8 can be eliminated from consideration. After applying this strategy, it can be noticed that using advanced singles or subsets is not necessary for completing the puzzle.
Example2:
In the second example, a Naked Pair is formed within a block: cells R4C5 and R5C6, both within Block 5, are restricted to the possibilities of 8 and 9. These two digits can fill these two cells in some order, so 8 and 9 can be excluded in all other cells within that block.
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