Naked single
Only one candidate remains in a cell, so that digit must go there.
The only remaining candidate in R7C7 is 5. Place 5 there.
What to look for
Choose an empty cell and rule out the digits already in its row, column and box. A candidate is a digit that could still go in the cell.
Why it works
Every cell needs a digit. If every other digit has been ruled out, the remaining candidate must be correct.
Try it step by step
- Check the filled digits in the cell's row, column and box.
- Remove those digits from its candidates.
- If only one candidate remains, fill in that digit.
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: 332429 · Play this puzzle from the start
A simple example
If a cell's only candidate is 5, it must contain 5, even if several other cells in the row are still empty.
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.