What is candidate mode in Sudoku?
Candidate mode in Sudoku lets you enter small possible digits in an unsolved cell instead of committing to one answer. On paper these are called pencil marks. As the puzzle develops, you remove candidates that conflict with a digit placed in the same row, column, or box.
When to use candidate mode
Easy puzzles can often be solved by scanning without writing every possibility. Candidate mode becomes useful when several cells have two or three possible digits and you need to compare them across a unit. Complete, accurate candidates reveal hidden singles, pairs, triples, and advanced patterns.
Keep candidates useful
For printed puzzles, place pencil marks lightly near consistent corners of each cell. The diagrams in the Sudoku tips guide show how candidate notes support techniques such as pairs, pointing, and X-Wing.
- Write only digits that are legal in the cell's row, column, and box.
- Remove a candidate immediately when that digit is placed in a peer cell.
- When only one candidate remains, write it as the cell's answer.
- Scan for digits that appear as a candidate in only one cell of a row, column, or box.