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Learn Sudoku Strategy
Every technique you need, from your first naked single to fish, wings, uniqueness and chains, each explained on a real board you can study. Work down the list and you'll solve any logic Sudoku without ever guessing.
Beginner
Intermediate
- Locked Candidates (Pointing & Claiming)Master locked candidates: when a digit in a box is confined to one row or column, eliminate it elsewhere. Pointing and claiming explained.
- Naked PairsLearn naked pairs: two cells in a unit sharing the same two candidates let you remove those digits from every other cell of the unit.
- Hidden PairsLearn hidden pairs: when two digits can only go in the same two cells of a unit, strip every other candidate from those cells.
- Naked Triples & QuadsLearn naked triples and quads: three or four cells in a unit sharing the same three or four candidates, letting you eliminate those digits everywhere else in the unit.
- Hidden Triples & QuadsLearn hidden triples and quads: three or four digits confined to the same three or four cells of a unit, letting you strip every other candidate from those cells.
Advanced
- The X-WingMaster the X-Wing: when a digit sits in exactly two cells of two rows that share the same two columns, eliminate it from the rest of those columns.
- The XY-WingLearn the XY-Wing: a three-cell pincer of bi-value cells that eliminates a shared candidate wherever the two pincers overlap.
- Swordfish & JellyfishMaster the Swordfish: a three-line fish where one digit confined to three rows across three columns is eliminated from the rest of those columns. Jellyfish too.
- The SkyscraperLearn the Skyscraper: two strong links of one digit that share a base line, letting you eliminate the digit from any cell that sees both far ends.
- The Two-String KiteLearn the Two-String Kite: a row strong link and a column strong link of one digit, joined through a box, that eliminate the digit from the cell seeing both free ends.
- The Empty RectangleLearn the Empty Rectangle: when a digit's candidates in a box fit one row plus one column, a crossing strong link lets you eliminate the digit from a far cell.
- The XYZ-WingLearn the XYZ-Wing: a three-candidate pivot with two bi-value pincers sharing a digit Z, eliminating Z from any cell that sees all three.
- The W-WingLearn the W-Wing: two matching bi-value cells {X,Y} joined by a strong link on X, letting you eliminate Y from any cell that sees both.
Expert
- The Unique RectangleLearn the Unique Rectangle: four cells in two boxes sharing a bi-value pair would create two solutions, so you can eliminate candidates that would allow it.
- BUG and BUG+1Learn BUG+1: when every unsolved cell but one is bi-value, the single three-candidate cell must take the digit that appears three times in its units.
- Simple ColoringLearn simple coloring: trace one digit through its conjugate pairs, two-color the chain, then eliminate by the color-trap and color-wrap rules.
- X-ChainsLearn the X-Chain: a single-digit chain alternating strong and weak links that starts and ends on a strong link, eliminating the digit from cells seeing both ends.
- XY-ChainsLearn the XY-Chain: a chain of bi-value cells linked by shared digits whose two ends carry a common digit Z, eliminating Z from any cell seeing both ends.
- Finned & Sashimi FishLearn finned and Sashimi fish: an X-Wing or Swordfish that almost works but for a few extra candidates in one box, still forcing eliminations that see every fin.
- ALS-XZ (Almost Locked Sets)Learn the ALS-XZ rule: two almost-locked sets sharing a restricted common digit and a second digit Z let you eliminate Z wherever it sees both sets.
Put it into practice
Stuck on a real puzzle? Drop it into the step-by-step solver — it names each technique as it solves, linking straight back to these guides.
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