Swordfish
A digit's candidates in three rows are confined to three columns. Remove that candidate from the rest of those columns.
In rows 3, 6 and 9, candidate 5 appears only in columns 1, 7 and 9. These 3 rows each need the digit once, with no two placements in the same column. The placements must therefore use all 3 columns. Remove candidate 5 from those columns outside rows 3, 6 and 9.
What to look for
Choose a digit and find three rows whose candidates for that digit fall within the same set of three columns. Each row can have the digit in two or three of those columns.
Why it works
The digit must appear once in each of the three rows, using three different columns. No cell in those columns outside the three rows can contain it.
Try it step by step
- Choose a digit and three rows.
- Check that their candidate positions cover exactly three columns.
- Remove that candidate from the three columns outside the selected rows. The same method works with rows and columns swapped.
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: 67463 · Play this puzzle from the start
A simple example
If the only candidates for 7 in rows 2, 5 and 8 are in columns 1, 4 and 9, remove candidate 7 from those columns in every other row.
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.