Full house
EasyWhen a row, a column or a box has a single empty cell left, that cell takes the one digit still missing there. It is the easiest step in sudoku, and the last one in every row, column and box.
How to spot it
- Count the empty cells of a row, a column or a box.
- If only one is left, find which digit from 1 to 9 is missing.
- Write it in.
Why it works
A row, column or box holds each digit once: with eight of them there, the ninth has only one place left.
Example
7
1
8
5
6
4
2
3
9
2
3
8
1
9
7
6
9
5
2
7
3
8
1
8
2
3
9
5
6
4
7
9
5
7
6
4
8
3
1
2
3
6
4
1
2
7
8
2
6
3
5
7
5
7
1
8
3
4
3
9
7
5
2
Column 2 has a single empty cell left.
Common mistakes
- Missing that a cell is the last one: count the empty cells, don’t guess from a glance.
- Writing a digit the unit already has: check all nine before writing.