Single Candidate (Naked Single)

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Single Candidate (Naked Single)

What It Is

A single candidate (naked single) is an empty cell with only one possible number left. After penciling candidates or eliminating others, that lone digit must fill the cell.

When to Use

Always watch for naked singles, especially after cross-hatching or simple eliminations. In straightforward puzzles, many cells quickly dwindle to one option.

How to Spot a Naked Single (Step-by-Step)

  1. List candidates: check which numbers 1–9 are missing in the cell’s row, column, and box.
  2. Identify sole options: if only one number is possible, you’ve found a naked single.
  3. Place the number: fill in that lone candidate as the solution.
  4. Eliminate and update: remove it from candidate lists of peers; this often creates new singles.
  5. Repeat: keep scanning for other cells that have dwindled to one option.

Naked singles are satisfying because they are 100% certain: when a cell sees eight digits around it, the missing digit is the solution. Each new placement can cascade into more singles.

See also

Scanning / Cross-Hatching Single Candidate (Naked Single) Single Position (Hidden Single) Naked Pairs / Triples / Quads Hidden Pairs / Triples / Quads Pointing Pairs / Triples (Locked Candidates Type 1) Box–Line Reduction (Locked Candidates Type 2) X-Wing Swordfish Jellyfish XY-Wing XYZ-Wing W-Wing Alternating Inference Chains (AICs) Forcing Chains / Forcing Nets Nishio Coloring Multi-Coloring Uniqueness Techniques (Unique Rectangle etc.) Fish Variants (Finned X-Wing, Sashimi etc.) ALS Techniques (ALS-XZ, ALS Chains) Sue de Coq Pattern Overlay / Template Method
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