In box 5, the digits 5, 7, 8 and 9 can go only in the 4 highlighted cells. Those cells are reserved for these digits, so remove all other candidates from them.
What to look for
Find four digits whose candidate positions, taken together, cover exactly four cells in one row, column or box.
Why it works
The four digits need all four cells. Each of those cells must contain one of the four digits, so no other candidates can remain.
Try it step by step
- Choose four digits in one house.
- Check that all their candidate positions fall within exactly four cells.
- Remove every other candidate from those four cells.
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: 222319 · Play this puzzle from the start
A simple example
If 1, 2, 3 and 4 are candidates only in four cells of a row, remove any candidates 5-9 from those cells.
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.