sudokUI › Sudoku techniques › Hidden Single
Hidden Single in sudoku
1-fish · hidden subset of one · how it fits
In a row, column or box, a digit X is a candidate in exactly one cell, whatever other candidates that cell may hold.
Why it works
Every unit must contain X once, and only one cell in this unit can still take it, so X is placed in that cell.
How to spot it
Take one digit at a time, rule out every cell that sees a placed copy, and look for a unit with one place remaining.
Worked example
Hidden Single: 1 fits only in r2c2 within row 2.
Practise it on a real puzzle. sudokUI generates a puzzle that needs Hidden 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 Hidden Single, the puzzle's difficulty rating grows by 14. Its class is Beginner. It is needed in 94% of puzzles that sudokUI generates. How the rating works.