What Is Auto Candidate Mode in Sudoku?
Quick answer
Auto candidate mode fills empty Sudoku cells with small possible digits, usually by excluding numbers already placed in the same row, column, and box. It saves note-taking, but a listed candidate is not a proven answer. Manual notes let you record possibilities and remove candidates as you make logical deductions.
One cell: what should the automatic notes show?
Find r2c1: row 2 from the top, column 1 from the left. The outlined empty cell is the focus. Check the placed digits, not the notes in neighboring cells.
- Row 2: exclude 4, 6, 7.
- Column 1: also exclude 2. The 4 and 6 are already excluded.
- Top-left box: also exclude 1. The 2 and 7 are already excluded.
Start with 1–9.
Remove 1, 2, 4, 6, 7.
Keep 3, 5, 8, 9.
All four digits fit the placed numbers around r2c1. That does not prove that any one of them is the answer. If an app shows only these basic candidates, this is the set to expect before further deductions.
Automatic or manual: choose the skill to practice
- Manual pencil marks
- You enter the possible digits yourself. This is useful for learning to check all three constraints. Missing a legal candidate can create a false single or pair.
- Automatic candidates
- The app generates the initial options. This reduces transcription work so you can focus on patterns. Whether it updates after placements or preserves your own deletions depends on the app.
- Automatic note cleanup
- Removing a newly placed digit from neighboring notes is different from filling all candidates. An app may offer either feature, both, or additional logic-based cleanup.
This explains common Sudoku interface terms, not a promise that Sudoku Coach has a particular toggle or setting. For the fundamentals, read how candidate notes work; for timing, read when to start using notes.
Before refreshing all notes, protect your deductions
Basic candidates answer “does this digit conflict with a placed number?” Logical eliminations answer a stronger question: “can this digit survive the pattern I just proved?” A digit can pass the first test and fail the second.
For example, a Naked Pair can remove a digit from another cell even when no matching digit has been placed in that cell’s row, column, or box. A basic refill may put that note back. Do not treat a restored note as evidence that your deduction was wrong.
- Before deleting a candidate, be able to state the rule that eliminates it.
- Check whether the app preserves manual eliminations when you refill notes.
- If you are unsure how a note disappeared, recheck its evidence before using a single or pair that depends on it.
Frequently asked questions
Does auto candidate mode solve the puzzle?
Basic auto candidates only apply the row, column, and box exclusions. A cell with several notes still needs a deduction. Some apps also offer solver-based hints or extra note cleanup; check the specific feature rather than assuming all auto modes work alike.
Why did a candidate I removed come back?
A full recalculation may restore a digit that fits the placed numbers but was ruled out by a pattern such as a pair. Apps differ in whether they preserve manual eliminations. Keep the reason for your elimination and check the refresh behavior.
Is using automatic candidates cheating?
For personal practice, choose the assistance that matches your goal. Write notes manually to practice basic exclusions; use automatic notes to focus on recognizing patterns. In a competition, follow its rules on assistance.
Next: tell a one-candidate cell from a one-place digit, or use the stuck-puzzle checklist.