🔥 Advanced Sudoku Techniques – X-Wing, Swordfish, and More

Take your Sudoku skills to the next level. This guide dives into advanced solving methods used by expert players to handle puzzles with minimal clues. Perfect for Level 14–20 at Sudoku99.

🧠 What Makes Sudoku "Advanced"

Advanced Sudoku puzzles typically contain fewer clues (17–25) and require pattern-based logic rather than simple elimination. Techniques used at this level focus on interrelated candidates across rows, columns, and boxes.

🔺 X-Wing Technique

The X-Wing involves identifying two rows (or columns) where a candidate appears exactly twice in the same columns (or rows). This forms a rectangle. You can eliminate that candidate from other cells in those columns (or rows).

• Use: Candidate reduction.
• Best for: Level 15–17 puzzles.

🐟 Swordfish

A larger version of X-Wing involving three rows and columns. It's rare but powerful, allowing candidate eliminations that can break a puzzle open when you're stuck.

• Use: Strategic pruning of possible numbers.
• Best for: Level 17–19 puzzles.

🔀 XY-Wing

Based on three cells that form a pivot and two wings. The pivot contains two candidates (X,Y), and the wings (X,Z) and (Y,Z) are connected by units. You can eliminate Z from other cells in the shared unit.

• Use: Logical inference based on cell relations.
• Best for: Level 16–18 puzzles.

♻️ Color Chain & Forcing Chains

Coloring is used to track two candidates (true/false) across the grid and detect contradictions. Forcing chains follow a trail of implications, often resolving tough puzzles logically without guessing.

📘 Practice Puzzle

🎓 Pro Tips

• Always use pencil marks. Many advanced techniques rely on candidates being visible.
• Track changes: after each move, check for ripple effects on other cells.
• Don’t guess. Every puzzle here has a logical path to solve.

📚 Keep Practicing

• Expert Book (Level 13–20)
• Extreme Challenge – 5000 Puzzles

❓ FAQs for Advanced Solving

Can I solve Level 20 puzzles without guessing?

Yes. All puzzles on Sudoku99 are logic-solvable. Techniques like Swordfish and forcing chains often help here.

What’s the difference between X-Wing and Swordfish?

X-Wing uses two rows/columns, Swordfish uses three. Both target a single candidate for elimination.

How can I practice daily?

Visit Level 20 Today to challenge yourself with a fresh expert puzzle every day.