Sudoku Techniques and Strategies

Whether you’re a beginner or an expert, mastering a variety of Sudoku techniques will help you solve puzzles of any difficulty. Below you’ll find a comprehensive list of strategies, each with a brief explanation and a link to a detailed guide.

Basic Techniques

• Naked Single
  Use when a cell has only one possible candidate. This is the most fundamental and frequently used technique in all puzzles.

• Hidden Single
  Use when a candidate appears only once in a row, column, or box, even if the cell has other candidates.

Intermediate Techniques

• Naked Pair
  Use when two cells in a unit contain only the same two candidates. Eliminate those candidates from other cells in the unit.

• Hidden Pair
  Use when two candidates appear only in the same two cells within a unit, even if those cells have other candidates.

• Naked Triple
  Use when three cells in a unit contain only the same three candidates (in any combination). Remove those candidates from other cells in the unit.

• Hidden Triple
  Use when three candidates appear only in the same three cells within a unit, even if those cells have other candidates.

• Naked Quad Use when four cells in a unit contain only the same four candidates. Eliminate those candidates from other cells in the unit.

• Hidden Quad Use when four candidates appear only in the same four cells within a unit, even if those cells have other candidates.

• Pointing Pair / Pointing Triple Use when a candidate is confined to one row or column within a box. Eliminate that candidate from the same row or column outside the box.

• Box-Line Reduction (Box/Line Interaction) Use when a candidate is restricted to a single row or column within a box, allowing you to eliminate it from the rest of that row or column.

Advanced Techniques

• X-Wing
  Use when a candidate appears exactly twice in two different rows and the columns match. Eliminates that candidate from other cells in those columns.

• Swordfish
  An extension of X-Wing involving three rows and columns. Use when a candidate appears in three rows and the columns align.

• Jellyfish
  A further extension involving four rows and columns. Use for very advanced puzzles with complex candidate patterns.

• XY-Wing
  Use when three cells form a pivot and two pincers, allowing you to eliminate a candidate from other cells that see both pincers.

• XYZ-Wing
  A more advanced version of XY-Wing involving three cells with overlapping candidates, allowing for further eliminations.

• WXYZ-Wing
  An even more advanced wing technique involving four cells and four candidates.

• Coloring Use chains of candidates to find contradictions and eliminate possibilities.

• Chains (AIC, Nice Loops) Follow alternating inference chains to deduce eliminations or placements.

• Unique Rectangle Use the puzzle’s uniqueness property to avoid deadly patterns and eliminate candidates.

• Finned X-Wing / Finned Swordfish Variations of X-Wing and Swordfish with extra candidates (“fins”) that allow further eliminations.

• BUG (Bivalue Universal Grave) Recognize and resolve situations where only bivalue cells remain.

• ALS (Almost Locked Sets) Advanced technique involving sets of candidates in overlapping cells.

• Skyscraper Pattern-based elimination involving two strong links in different rows or columns.

• Kite A pattern that allows candidate elimination based on the interaction of rows, columns, and boxes.

• Empty Rectangle
  Eliminate candidates by analyzing empty rectangles and their interactions with strong links.

• Sue de Coq A complex technique involving the interaction of candidates in overlapping units.

When to Use Each Technique

• Basic techniques are used in every puzzle and should always be your starting point.
• Intermediate techniques become necessary as puzzles get harder and basic methods no longer yield progress.
• Advanced techniques are typically required for the most challenging puzzles, such as those labeled “hard,” “expert,” or “evil.”

Explore each technique above to learn how and when to apply it. Mastering these strategies will help you solve even the toughest Sudoku puzzles!