sudokUI › Sudoku techniques › Naked Single
Naked Single in sudoku
naked subset of one · how it fits
An empty cell has exactly one candidate left, every other digit having been ruled out for that cell.
Why it works
Every cell must hold a digit, and eight of the nine have been excluded here, so the one remaining candidate is placed in the cell.
How to spot it
Look for empty cells whose row, column and box between them already show many different digits, then check whether only one digit is left.
Worked example
Naked Single: r4c1 has only one candidate left, 1.
Practise it on a real puzzle. sudokUI generates a puzzle that needs Naked Single and takes you straight to the position where it applies. Hints draw the pattern on the board and explain the step.
In a puzzle's rating
Each time the solver needs Naked Single, the puzzle's difficulty rating grows by 4. Its class is Beginner. It is needed in every puzzle that sudokUI generates. How the rating works.