Techniques · Easy

Hidden Single

A digit has to appear once in every row, column and box. When all but one cell of a unit are ruled out for a digit, that digit must go in the remaining cell, even if the cell itself still has other candidates.

How to spot it

Pick a digit and a box. Follow the rows and columns where that digit is already placed and cross off the cells they cover. If one empty cell is left in the box, the digit goes there. Boxes are the quickest place to find these.

Example

In row 1, 6 can only go in r1c6 (Hidden Single).

the pattern the cell it solves