AI Summary
This guide explains candidate mode in Sudoku apps, when to use it, and how it speeds up solving without guessing. It covers light notes, full notes, workflows, and common mistakes.
AI Highlights
- Candidate mode: Digital pencil marks for logical possibilities.
- Timing matters: Use it after scanning stalls.
- Clean notes: Removing candidates is as important as adding them.
- Technique support: Pairs, triples, and fish patterns depend on candidates.
- Workflow: Scan, note, eliminate, rescan.
What Is Candidate Mode?
Candidate mode is the digital version of pencil marks. It lets you place small digits in a cell to show possible values. These candidates are not guesses. They are logical options based on the current grid and the row, column, and box constraints.
When Should You Use It?
Candidate mode is most helpful in medium and hard puzzles. Easy puzzles often solve with scanning alone. When a grid stops giving singles, candidates reveal hidden structure and open the next step. Think of it as a tool for clarity, not something you must use from the start.
Light Notes Vs Full Notes
Light notes are fast and keep the grid readable. Full notes list all possible digits and are better for hard puzzles. A practical approach is to start with light notes in the toughest box. If you still cannot progress, expand to full notes in the surrounding boxes, not the entire grid.
How To Use Candidate Mode Efficiently
- Scan rows, columns, and boxes for singles.
- Add candidates only where needed, not everywhere.
- Check for hidden singles and hidden pairs.
- Remove candidates after every placement.
- Rescan the affected row, column, and box.
Candidate Mode And Techniques
Many techniques rely on candidates. Without clean notes, advanced patterns are nearly invisible.
- Hidden pairs: Two digits appear only in two cells.
- Triples: Three digits confined to three cells.
- Box line reduction: Candidates in a box align in one row or column.
- Fish patterns: Candidate positions align across rows and columns.
Why Clean Candidates Matter
Messy candidates hide patterns. A correct candidate list turns the grid into a map. A sloppy list turns it into noise. Remove candidates immediately after placing a digit and rescan the affected units so your notes stay trustworthy.
Example Workflow
Suppose you solve all singles and the grid stalls. You add candidates in one box. You notice digit 7 appears only twice in that box, forming a hidden pair with digit 3. You remove other candidates from those two cells, which creates a new single in the row. That single unlocks the next step and the grid opens again.
Candidate Mode Styles
- Box-first: Fill candidates in one box to spot pairs quickly.
- Digit-first: Track one digit across the grid to find hidden singles.
- Hybrid: Use light notes everywhere, full notes only where stuck.
Common Mistakes
- Over marking: Filling every candidate creates noise.
- Not cleaning: Stale candidates hide the next move.
- Switching modes too often: Use a steady flow.
- Guessing: Candidate mode is a logic tool, not a guess aid.
Practice Drill
Pick one medium puzzle. Solve the first half without candidates. When you stall, turn on candidate mode and add notes in one box. Find one hidden single or pair, then clear the candidates and rescan the grid. Repeat in the next box.
Checklist
- Scan for singles before adding notes.
- Use light notes first.
- Clean candidates after every placement.
- Rescan the affected units.
- Only expand to full notes if stuck.
FAQ
Q1: Should I use full candidates?
Full candidates help on hard puzzles, but selective notes are faster for medium ones.
Q2: Does candidate mode slow me down?
It slows you initially but speeds up solving once you find patterns faster.
Q3: Is candidate mode required?
No, but it makes advanced techniques much easier to apply.
Summary
Candidate mode is a powerful tool for efficient solving. Use it when a puzzle stalls, keep candidates clean, and rely on them to spot pairs, line interactions, and advanced patterns. With practice, your solving becomes faster and more reliable.
Extended Practice Guide
To build real speed with candidate mode, practice in small cycles. Solve one easy puzzle without candidates, then solve one medium puzzle using light notes only. Finally, take a harder puzzle and use full candidates in just two boxes. This sequence teaches you when to switch modes without overloading the grid.
When using light notes, focus on three tasks: find hidden singles, confirm hidden pairs, and clean candidates after every placement. This keeps your notes short and readable while still giving you enough structure to make progress.
Full notes should feel temporary. Use them to identify one strong elimination, then return to scanning. The goal is not to keep a fully marked grid, but to unlock the next step.
Example Walkthrough
Imagine a box where the digit 8 appears only in two cells. You mark those cells and remove 8 from the rest of the row and column. That removal creates a hidden single in another box. This chain happens often, and candidate mode makes it visible quickly.
Candidate Mode Checklist
- Scan for singles before adding any notes.
- Add candidates only in the most constrained area.
- Look for hidden singles after adding notes.
- Remove candidates immediately after placements.
- Rescan the affected row, column, and box.
Extra Tips
- Zoom in: If using a mobile app, zoom to avoid misclicks.
- Color mode: Some apps allow colored candidates; use it to track one digit.
- Undo wisely: If a grid feels messy, undo a few steps and clean notes.
Deep Dive: When To Switch Modes
Candidate mode is most effective when you are no longer getting singles from a basic scan. The moment you feel like you are guessing, pause and add candidates in the tightest box. This usually has the fewest possibilities, so it provides the quickest clues. Once that box yields a pair or a hidden single, return to normal scanning. The goal is to use candidates to unlock the next step, not to fill the grid with notes.
Full candidates are powerful but expensive. They take time and can overwhelm your eyes, so use them in limited zones. Many solvers mark candidates only in two or three boxes at a time, which keeps the grid readable and still lets you apply mid-level techniques. If you feel stuck for longer than two scan cycles, switch a small region to full notes and look for a single elimination to restart the puzzle.
Apps often have tools like auto-candidate or highlight. Use them sparingly. Auto-candidate can save time, but it can also reduce your engagement with the logic. If you use it, immediately clean candidates after each placement so the grid stays accurate.
Step-by-Step Example
Imagine a box where digits 2, 4, and 9 appear only in three cells. After you add candidates, you notice those digits are confined to those cells. You remove all other candidates from the trio. This reveals a hidden single in the row that intersects the box. That single then clears a column, opening the next move. Candidate mode makes this chain visible in seconds.
A similar pattern happens with line interactions. If a candidate in a box only appears in one row, you can eliminate that candidate from the rest of the row. This elimination often produces a single without any advanced technique.
Candidate Mode Checklist
- Scan for singles before adding notes.
- Start candidates in the most constrained box.
- Look for hidden singles and hidden pairs first.
- Clean candidates after every placement.
- Rescan the affected row, column, and box.
- Limit full notes to small areas.
- Use digit-focused scans when stuck.
- Stop once a new single appears.
FAQ
Q1: Is auto-candidate cheating?
No, but it can reduce your engagement. Use it if you still practice the logic.
Q2: How many candidates should I write?
Enough to reveal structure. If the grid feels noisy, reduce them.
Q3: Should I always use full candidates on hard puzzles?
Not always. Start with light notes and expand only where needed.