Hidden Single Sudoku Strategy
A hidden single happens when a digit can appear in only one cell within a row, column, or 3×3 box — even if that cell has multiple pencil marks.
Example
In a 3×3 box, the digit 3 might be possible in three cells. Two of those cells are in the same row. The third cell is the only place 3 can go in that box.
How to find hidden singles
- Pick one digit (1–9).
- Scan each row, column, and box for where that digit can still go.
- If only one cell remains, place the digit.
Hidden singles are easy to miss without pencil marks.
Practice loop
After placing obvious digits, update pencil marks, then search for hidden singles in rows, columns, and boxes.