Full house
A row, column or box has just one empty cell. Fill it with the missing digit.
In column 2, eight cells are already filled. The missing digit is 3, so place it in R1C2.
What to look for
Look for a row, column or 3 × 3 box with eight filled cells. Each of these groups is called a house.
Why it works
Each house must contain the digits 1-9 exactly once. With eight digits already filled in, only the missing digit can go in the last cell.
Try it step by step
- Check the eight filled cells in the row, column or box.
- Find the missing digit from 1-9.
- Fill the empty cell, then check its row, column and box for new opportunities.
Try it on a real puzzle
Start with the highlighted step, then keep solving. Use "Apply hint" to make the suggested change, or enter your own digits and candidate notes. Use "Undo" to reverse your last change.
| C1 | C2 | C3 | C4 | C5 | C6 | C7 | C8 | C9 | |
|---|---|---|---|---|---|---|---|---|---|
| R1 | |||||||||
| R2 | |||||||||
| R3 | |||||||||
| R4 | |||||||||
| R5 | |||||||||
| R6 | |||||||||
| R7 | |||||||||
| R8 | |||||||||
| R9 |
Use the arrow keys to move, 1-9 to enter a digit and Backspace or Delete to clear a cell. To add or remove a candidate, press C and then 1-9.
Source puzzle number: 148634 · Play this puzzle from the start
A simple example
If a row contains 1, 2, 3, 4, 5, 6, 7 and 9, its empty cell must be 8. The same reasoning works in a column or a box.
A house is a row, column or 3 × 3 box. A line is a row or column. Two cells "see" each other when they share a house. R1C3 means row 1, column 3. Boxes are numbered 1-9 from left to right and top to bottom. Braces such as {1, 2} show a cell's candidates, not confirmed digits.