Learn / Foundations
Sudoku technique · Foundations · first needed in Calm puzzles
Full house
One empty cell in a row, column, or box means just one digit is missing.
How to spot it
Count the filled digits in the highlighted house.
The common mistake
A nearly filled house is useful, but only one remaining cell makes a full house.
Learn this first
Candidates and the row / column / box rules.
A worked example
This position comes from SudokuByte’s lesson on the Full house. Gold cells hold the evidence; green cells are the pattern’s ends.
256
28
4568
7
1
89
346
2569
23459
1257
3
158
6
4
89
17
1259
2579
167
9
146
3
2
5
1467
8
47
2359
28
3589
49
389
1
3468
7
23489
4
6
7
5
389
2
138
19
389
239
1
389
49
7
6
5
29
23489
19
7
19
8
5
3
2
4
6
69
5
2
1
9
4
78
3
78
8
4
3
2
6
7
9
5
1
256
28
4568
7
1
89
346
2569
23459
1257
3
158
6
4
89
17
1259
2579
167
9
146
3
2
5
1467
8
47
2359
28
3589
49
389
1
3468
7
23489
4
6
7
5
389
2
138
19
389
239
1
389
49
7
6
5
29
23489
19
7
19
8
5
3
2
4
6
69
5
2
1
9
4
78
3
78
8
4
3
2
6
7
9
5
1
Where to look
Count the filled digits in the highlighted house.One empty cell in a row, column, or box means just one digit is missing.
Read the evidence in this position
box 8 contains eight filled digits. r8c5 is its only empty cell.Why the deduction must follow
There is no alternative left for r8c5. Candidate reductions can reveal a placement without any trial or guess.Apply the result
Place 9 in r8c5.
Further reading: hodoku.sourceforge.net