Single Candidate
Find cells where only one number can legally be placed based on current puzzle state.
How to Apply
- 1Check empty cells in a region (row, column, or 3x3 box)
- 2List possible numbers for each cell
- 3Look for cells with only one possible number
- 4That number must go in that cell
Example
If a cell can only contain 4 based on the rules, then 4 is the answer.
Hidden Singles
Identify numbers that can only appear in one position within a row, column, or box.
How to Apply
- 1Look at all empty cells in a region
- 2List possible numbers for each cell
- 3Find numbers that only appear once in the lists
- 4That number must go in that cell
Example
If 7 can only go in one cell of a row, even if that cell has other possibilities, 7 must go there.