Techniques

Swordfish Technique: Advanced Sudoku Solving Method

Saturday, November 22, 2025

Introduction

The Swordfish technique is a powerful, advanced Sudoku pattern that helps eliminate candidates using a three-row, three-column linking structure. It is essentially the "3×3 version" of the X-Wing: instead of two rows and two columns, Swordfish uses three rows and three columns, creating a flexible elimination grid for a single digit.

This technique typically appears in harder puzzles where traditional strategies fail, making it an essential tool for solvers aiming to master late-game logic without guessing.

What Is the Swordfish Technique?

Swordfish occurs when a digit appears:

  • In exactly two or three cells
  • Across three different rows
  • All these possibilities align within three identical columns

Or the pattern can be reversed:

  • Across three columns
  • Within three rows

This creates a structure where the candidate is "locked" into those row–column intersections, forming a repeating grid pattern resembling the shape of a swordfish.

In short:

If a digit's candidate positions in three rows are limited to the same three columns, then that digit must occupy those three rows × columns.

Therefore, that digit can be eliminated from all other cells in those columns.

Swordfish is one of the cleanest advanced elimination techniques once you learn how to spot the pattern.

Key Points

Understanding Swordfish is essential for advanced solving:

  • 3×3 extension of X-Wing: Uses three rows/columns instead of two, creating more flexible eliminations
  • Advanced technique: Appears in harder puzzles where basic methods are insufficient
  • Pattern recognition: Requires practice to identify the three-row, three-column linking structure
  • Powerful eliminations: Can eliminate multiple candidates across multiple columns/rows simultaneously
  • Logical foundation: Builds on X-Wing concepts, leading to understanding Jellyfish and other advanced methods

How It Works (Step-by-Step)

Here's the systematic approach to identifying and using Swordfish:

Step 1: Complete Pencil Marking

Ensure all candidates are marked throughout the grid. Swordfish patterns are only visible with complete candidate information.

Step 2: Choose a Number to Check

Select one number (1-9) to search for Swordfish patterns. Check each number systematically.

Step 3: Scan Rows for Pattern

Look for three rows where your chosen number appears in exactly two or three cells. Note which columns these cells occupy.

Step 4: Verify Column Alignment

Confirm that all candidate positions fall within the same three columns. This creates the Swordfish structure.

Step 5: Make Eliminations

Remove your chosen number from all other cells in those three columns (excluding the Swordfish pattern rows).

🧩 2. Visual Representation of Swordfish

Here is an ASCII-style visualization for candidate 8:

      C1   C5   C9
R2     8    .    8
R5     .    8    .
R8     8    .    8

This shows:

  • R2 contains 8 in C1 and C9
  • R5 contains 8 in C5 (and one more candidate not shown here)
  • R8 contains 8 in C1 and C9
  • All candidates occur within the same three columns
  • And the rows involved are three distinct rows

This creates the Swordfish structure.

🗡️ 3. Why It's Called "Swordfish"

Like X-Wing and Jellyfish, the pattern is named after ocean animals. Swordfish patterns resemble a triangular grid or a cross-hatched fishing net, with the candidates forming three repetitive "arms" across the puzzle.

The name simply helps solvers remember the structure visually.

🔍 4. Step-by-Step Example

Consider candidate 5:

  • Row 1 has 5s in C2, C7
  • Row 4 has 5s in C2, C9
  • Row 9 has 5s in C7, C9

This means the 5s are limited to Columns 2, 7, and 9 across these three rows.

Because:

  • R1 → (C2, C7)
  • R4 → (C2, C9)
  • R9 → (C7, C9)

We can conclude:

One of these three rows will contain a 5 in each of the three columns (2, 7, 9).

Therefore:

All other 5s in columns 2, 7, and 9 (outside R1, R4, R9)

→ must be eliminated.

This often triggers immediate solving breakthroughs, opening up new singles, pairs, and box interactions.

🧠 5. When to Use Swordfish

Swordfish becomes necessary when:

  • ✔ Medium-level techniques stall
  • ✔ X-Wing patterns appear but cannot fully resolve
  • ✔ Multiple strong links appear across large regions
  • ✔ You're solving hard or expert puzzles
  • ✔ You want to avoid trial-and-error or guessing

Swordfish typically appears in puzzles where:

  • Pencil marks are well developed
  • The grid is around 40–70% solved
  • Advanced logic is required to progress

📌 6. Swordfish vs. X-Wing vs. Jellyfish

| Technique | Rows/Columns | Difficulty | Frequency | |-----------|--------------|-----------|-----------| | X-Wing | 2×2 | Easy–Medium | Common | | Swordfish | 3×3 | Medium–Hard | Uncommon | | Jellyfish | 4×4 | Expert | Rare |

Swordfish is the perfect middle ground for advanced but manageable logic.

🛠️ 7. How to Identify Swordfish Quickly

Below are efficient ways to recognize Swordfish patterns without scanning every row manually.

Method 1: Candidate Scanning

  • Pick a digit (1–9)
  • Check rows with exactly 2–3 candidates
  • Look for repeating column patterns
  • Confirm the 3×3 structure

Method 2: Box-Based Scanning

Swordfish often hides across:

  • The top/middle/bottom row band
  • The left/center/right column stack

This pattern is easier to spot visually.

Method 3: Pencil Mark Visualization

Pencil marks help identify:

  • Overlapping columns
  • Matching candidate distributions
  • Repeating "L-shaped" configurations

⚠️ 8. Common Mistakes Solvers Make

Mistake 1: Using rows with more than 3 candidates

Swordfish requires exact pairs or triplets.

Mistake 2: Eliminating from wrong cells

Candidates must be removed from:

  • The same columns
  • But outside the pattern's rows

Mistake 3: Confusing Swordfish with Three-String Kite or Skyscraper

Those share similarities but follow different elimination rules.

Mistake 4: Not confirming all three rows/columns match

Partial alignment is not enough.

🧩 9. Practical Tips for Learning Swordfish

Tip 1: Use color-marking

Mark candidates in three colors to distinguish row-block groupings.

Tip 2: Train with specific drills

Practice identifying:

  • 2-row repeating patterns (pre-X-Wing)
  • 3-row candidate alignments (pre-Swordfish)

Tip 3: Combine with chain techniques

Swordfish often appears before:

  • XY-Chains
  • Alternating Inference Chains
  • Turbot Fish

Tip 4: Don't force it early

Swordfish rarely appears in the early stage of puzzles.

🙋 Frequently Asked Questions

Q1: Is Swordfish mandatory for solving difficult puzzles?

Not always, but it appears frequently in harder logic-based puzzles.

Q2: How often does Swordfish occur?

In medium puzzles: seldom

In hard puzzles: occasionally

In expert puzzles: quite often

Q3: Should beginners learn Swordfish?

Not necessary. It's an intermediate-to-advanced tool.

Q4: How does Swordfish compare to chains?

Swordfish is simpler and more visual; chains are more powerful but harder.

Examples

Example 1: Standard Swordfish Pattern

Looking for number 5:

  • Row 1: 5 appears in columns 2 and 7
  • Row 4: 5 appears in columns 2 and 9
  • Row 9: 5 appears in columns 7 and 9

All candidates fall within columns 2, 7, and 9. We can eliminate 5 from all other cells in those columns.

Example 2: Column-Based Swordfish

The same logic works with columns: if a number appears in exactly two or three cells across three columns, and all positions align within three rows, eliminations occur in those rows.

Summary

The Swordfish technique is an essential strategy in your Sudoku arsenal once you enter the advanced levels of solving. This 3×3 extension of X-Wing uses three rows and three columns to create powerful elimination patterns that break through complex grid structures. By understanding how candidate positions align across multiple rows and columns, you unlock logical elimination methods that avoid guessing.

If you're aiming to tackle expert-level puzzles consistently, mastering Swordfish will dramatically elevate your solving precision and strategic depth. Practice pattern recognition, maintain complete pencil marks, and scan systematically for these advanced structures.

Ready to master Swordfish? Try our Sudoku puzzles and apply this advanced technique!

❓ FAQ

Q1: Is Swordfish mandatory for solving difficult puzzles?

Not always, but it appears frequently in harder logic-based puzzles. Many expert puzzles require Swordfish or similar advanced techniques to solve without guessing.

Q2: How often does Swordfish occur?

In medium puzzles: seldom. In hard puzzles: occasionally. In expert puzzles: quite often. The technique becomes more valuable as puzzle difficulty increases.

Q3: Should beginners learn Swordfish?

Not necessary. It's an intermediate-to-advanced tool. Master X-Wing first, then progress to Swordfish when ready for more complex patterns.

Q4: How does Swordfish compare to chains?

Swordfish is simpler and more visual; chains are more powerful but harder. Swordfish provides a good stepping stone between basic fish techniques and complex chain logic.

Q5: Can Swordfish work with columns instead of rows?

Yes! Swordfish works both ways: row-based (eliminates from columns) and column-based (eliminates from rows). Always check both orientations.

Q6: How is Swordfish different from X-Wing?

X-Wing uses 2 rows/columns, Swordfish uses 3. The logic is the same, just scaled up. Swordfish provides more elimination opportunities but requires more pattern recognition skill.

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