Sudoku Elimination by Row, Column, and Box

When placing candidates, eliminate impossibilities aggressively across rows, columns, and boxes.

The rules

• If 5 is in a row, remove 5 from pencil marks in every other cell in that row.
• Repeat for columns and boxes.

This cross-elimination often creates naked singles indirectly — you eliminate candidates until only one remains.

Reliable workflow

1. Place all obvious full-house digits.
2. Update pencil marks.
3. Find naked singles.
4. Find hidden singles in rows, columns, then boxes.
5. Repeat until the grid is complete.

Play Sudoku online and apply elimination after every placement.