Tips for Hard
Hard grids need notes. Once every cell has candidates, look for three cells sharing three digits, or an X-wing where a digit appears in the same two columns of two rows. Eliminating carefully beats guessing.
How sudoku works
Fill the 9×9 grid with the digits 1 to 9 so that each row, each column and each of the nine 3×3 boxes contains every digit once. The starting numbers (clues) cannot be changed, and every Comma Puzzles grid has exactly one solution.
A simple way to start
- Scan one digit at a time: pick a digit, say 5, and look for a box where only one cell can still hold it.
- Focus on one cell: remove every digit already in its row, column and box. Sometimes only one candidate is left.
- Take notes: press N or tap Notes to pencil in candidates. Placing a digit clears it from the notes in the same row, column and box.
- Use locked candidates: if a digit's candidates inside one box all sit on one row, that digit can be removed from the rest of that row.
How levels are set
Each new puzzle is solved by a logic engine that uses human techniques, and the hardest technique it needed sets the level. Easy needs only singles and starts with 36 to 40 clues. Medium may need locked candidates and pairs. Hard can call for triples or an X-wing, and Expert starts with only about 22 to 25 clues.