Swordfish

Swordfish is like X-Wing, but bigger: three rows and three columns instead of two. It's an advanced technique that can break through tough puzzles.

What is a Swordfish?

Look for this pattern:

• Pick a number (like 4)
• Find three rows where that number can only go in 2-3 spots each
• All those spots must fit within three columns

Unlike X-Wing's perfect rectangle, Swordfish can have "missing corners."

Visual Example

What's happening:

• Row 2: 4 can only go in columns 1 or 5
• Row 4: 4 can only go in columns 1 or 3
• Row 8: 4 can only go in columns 3 or 5
• All fit within three columns: 1, 3, and 5

The Logic Explained

Think about it step by step:

1. Row 2 needs a 4 somewhere — it must go in column 1 or 5
2. Row 4 needs a 4 somewhere — it must go in column 1 or 3
3. Row 8 needs a 4 somewhere — it must go in column 3 or 5
4. Three rows, three columns — each column gets exactly one 4

The key insight: No matter which cell gets the 4 in each row, the three columns will each contain exactly one 4 from these rows.

The result: No other cell in columns 1, 3, or 5 can have 4. They're "claimed" by the Swordfish!

After Elimination

Why "Missing Corners" Work

Unlike X-Wing which needs all 4 corners, Swordfish can have "gaps":

Why it still works:

• Each row still needs exactly one 4
• Those 4s must come from the three columns
• Even if a row doesn't use all three columns, the logic holds

Column-Based Swordfish

The same pattern works starting from columns instead of rows:

Column-based rules:

• Find three columns where a number can only go in 2-3 cells each
• Those cells share the same three rows
• Eliminate from other cells in those rows

How to Find Swordfish

Method 1: Row Scanning

1. Pick a candidate — Works best when it has few placements left
2. Find rows with 2-3 candidates — Note which columns they're in
3. Look for three rows — All fitting in exactly three columns
4. Eliminate! — Remove from other cells in those columns

Example thought process:

• "Row 2 has 4 in columns 1, 5"
• "Row 4 has 4 in columns 1, 3"
• "Row 8 has 4 in columns 3, 5"
• "Together: columns 1, 3, 5 — that's three columns!"
• "Swordfish found!"

Method 2: Column Grouping

1. For each candidate, list which columns contain it in each row
2. Look for three rows that share exactly three columns
3. Verify no row has the candidate in a 4th column

Method 3: Build from X-Wing

1. Find an almost-X-Wing (two rows, two columns)
2. Look for a third row that extends the pattern
3. Check if the third row fits within three total columns

Method 4: Visual Pattern

With practice, Swordfish becomes visual:

• A number that forms an irregular shape across three rows
• The shape stays within three columns
• No row has more than 3 positions for the candidate

The Exact Requirements

For a valid Swordfish:

The Elimination Process

Once you find a Swordfish:

1. Identify the three columns — Where the Swordfish cells are
2. Check each column — Find cells with the candidate outside Swordfish rows
3. Eliminate — Remove the candidate from those cells
4. Check for singles — The elimination might solve cells
5. Re-scan — The board changed, new patterns may exist

Swordfish vs. X-Wing

Practice Exercises

Exercise 1: Find the Swordfish

Exercise 2: Find and apply the Swordfish

Common Mistakes

Mistake 1: Wrong row count

• Swordfish needs EXACTLY 3 rows
• 2 rows = X-Wing (different technique)
• 4 rows = Jellyfish (different technique)

Mistake 2: Too many columns

All candidate positions must fit in EXACTLY 3 columns. If you need 4+ columns, it's not a Swordfish.

Mistake 3: Eliminating from wrong places

• Row-based Swordfish: eliminate from the columns
• Column-based Swordfish: eliminate from the rows
• NEVER eliminate from the Swordfish cells themselves

Mistake 4: Rows have too many candidates

If a row has 4+ cells with the candidate, that row can't be part of a Swordfish.

Mistake 5: Not checking both directions

Always check for both row-based AND column-based Swordfish. You might find one but miss the other.

When Swordfish Appears

• Easy puzzles: Never needed
• Medium puzzles: Rarely needed
• Hard puzzles: Occasionally useful
• Expert puzzles: Important technique
• Extreme puzzles: Essential skill

The Fish Family

Swordfish is part of a family of techniques:

All work the same way — just with different sizes!

Quick Reference

Swordfish definition:

• 3 rows with a candidate in 2-3 positions each
• All positions in exactly 3 columns
• Or: 3 columns with candidate in 2-3 positions, same 3 rows

Finding Swordfish:

1. Pick a candidate with few positions
2. Find three rows with 2-3 positions each
3. Check if all positions fit in 3 columns
4. Verify and eliminate

Elimination rule:

• Row-based: eliminate from columns (outside Swordfish rows)
• Column-based: eliminate from rows (outside Swordfish columns)

When to look:

• Expert+ puzzles
• After simpler techniques fail
• Candidates that have 6-9 positions left

What's Next?

Once you master Swordfish:

• Jellyfish — Same pattern with 4 rows and 4 columns
• Finned X-Wing — Fish patterns with extra "fin" cells
• XY-Wing — Three-cell chain technique