X-Wing

X-Wing is your first advanced technique. It finds a pattern across two rows and two columns, forming a rectangle that lets you eliminate candidates.

What is an X-Wing?

Look for this pattern:

• Pick a number (like 5)
• Find two rows where that number can only go in exactly two spots
• Those spots must line up in the same two columns

The four cells form a rectangle. That's an X-Wing!

Visual Example

What's happening:

• Row 2: The 5 can only go in column 1 or column 9
• Row 8: The 5 can only go in column 1 or column 9
• These four cells form a rectangle

The Logic Explained

Here's the key insight. There are only two possible outcomes:

Possibility 1:

• Row 2 gets its 5 in column 1
• Row 8 gets its 5 in column 9

Possibility 2:

• Row 2 gets its 5 in column 9
• Row 8 gets its 5 in column 1

Either way:

• Column 1 gets exactly one 5 (from row 2 or row 8)
• Column 9 gets exactly one 5 (from the other row)

The result: No other cell in columns 1 or 9 can have a 5. Those columns are "claimed" by the X-Wing!

After Elimination

After eliminating, check:

• Did any cell become a naked single?
• Did this create a hidden single somewhere?
• Can you now find other patterns?

Column-Based X-Wing

The same pattern works starting from columns instead of rows:

Column-based rules:

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

How to Systematically Find X-Wings

Method 1: Row Scanning

1. Pick a candidate — Start with numbers that still need placing
2. Go row by row — For each row, count cells with that candidate
3. Note rows with exactly 2 — Write down which columns they're in
4. Look for matches — Do any two rows share the same two columns?

Method 2: Candidate Counting

1. Pick a candidate
2. For each column, list which rows have it
3. Look for two columns with candidates in the same two rows
4. That's your X-Wing!

Method 3: Visual Pattern

With practice, you'll spot X-Wings visually:

• Look for a number that forms a rectangle shape
• Check if the corners are the ONLY places for that number in those rows
• If yes, you found one!

The Exact Requirements

For a valid X-Wing, you need:

Note: If a row has the candidate in only ONE cell (not two), that's a hidden single — just place it directly! X-Wings require exactly 2 cells per row.

What to Do After Finding an X-Wing

1. Make the eliminations — Remove the candidate from other cells in the affected columns (or rows)
2. Check for singles — The elimination might create naked or hidden singles
3. Look for chains — X-Wings often unlock other patterns
4. Re-scan — The board changed, so other X-Wings might now exist

Common Mistakes

Mistake 1: Wrong cell count

• The candidate must appear in EXACTLY 2 cells per row
• If a row has 3+ cells with the candidate, it's not part of this X-Wing

Mistake 2: Columns don't match

• Both rows must use the SAME two columns
• Row 2 in columns 1,4 and Row 5 in columns 2,4 = NOT an X-Wing

Mistake 3: Eliminating from the wrong place

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

Mistake 4: Forgetting to check both directions

• Always check for both row-based AND column-based X-Wings
• You might find one but miss the other

Why "X-Wing"?

If you draw lines connecting the four corners diagonally, they form an X shape. The pattern also resembles the shape of an X-Wing fighter from Star Wars!

When to Look for X-Wings

• Puzzle difficulty: Common in Hard and Expert, rare in Easy/Medium
• Best time: After basic techniques (singles, pairs) stop working
• Good candidates: Numbers that have been partially placed (4-6 left to place)

Practice Tips

1. Start with one number — Pick a number and check ALL rows for X-Wing potential
2. Use pencil marks — Full candidate notation makes X-Wings much easier to spot
3. Check eliminations carefully — Make sure you're eliminating from the right cells
4. Don't force it — Not every puzzle has an X-Wing

What's Next?

Once you master X-Wing, you're ready for:

• Swordfish — Same idea with 3 rows and 3 columns
• Jellyfish — Same idea with 4 rows and 4 columns
• Finned X-Wing — X-Wing with an extra cell that limits eliminations