Beginner · Easy
Hidden single
When a digit has only one place left in a row, column or box, it goes there.
Pick a digit and go through the rows, checking where it can still go. Other cells either hold a digit already or share a row, column or box with the same digit. When one cell is left, enter it.
The cell itself may still have several candidates, so looking at the cell won't show it; looking at the digit does.
This example, step by step
- Where to lookA pointer first: look at row 4. Where can 5 still go?
- Hidden singleIn row 4, 5 can only go in column 3.
In hints
When stuck, tap "Hint" for the next step. For a hidden single it marks the region and the cell, then explains why.