Sudoku Swordfish Technique Explained (Step-by-Step Guide) - SudokuPuzzles.net
Learn the Sudoku Swordfish technique with clear examples and diagrams. Master advanced strategies today with our comprehensive step-by-step guide.
The Swordfish technique is one of the most powerful advanced Sudoku solving methods, extending the concept of the X-Wing pattern to three rows and columns. This comprehensive guide will teach you everything you need to know about identifying and applying the Swordfish technique to solve challenging Sudoku puzzles.
What is the Swordfish Technique?
The Swordfish technique is an advanced pattern recognition method that operates on the principle of candidate elimination. It's named "Swordfish" because of the distinctive pattern it creates when visualized - resembling the skeletal structure of a swordfish.
This technique works when a specific digit appears as a candidate in exactly two or three cells across three different rows (or columns), and these cells align in such a way that they form a pattern across three columns (or rows).
Key Characteristics of Swordfish:
- Involves three rows and three columns
- Target digit appears in 2-3 cells per row
- All cells align to form a rectangular pattern
- Allows elimination of the target digit from other cells in the same columns
When to Use Swordfish in a Puzzle
The Swordfish technique becomes necessary when simpler elimination methods have been exhausted. Here's when to look for Swordfish patterns:
Prerequisites for Swordfish:
- Basic techniques exhausted: Single candidates, hidden singles, and naked pairs have been applied
- X-Wing patterns absent: No simpler fish patterns are available
- Puzzle difficulty: Typically found in Hard, Expert, or Master level puzzles
- Candidate distribution: A digit appears in multiple rows/columns with limited distribution
Visual Cues to Look For:
- A digit appears in exactly 2-3 cells in each of three different rows
- These cells are positioned to form a rectangular grid pattern
- The digit doesn't appear in other cells of those same rows
Step-by-Step Example
Let's work through a detailed example to understand how the Swordfish technique works in practice.
Example Setup:
Imagine we're solving a Sudoku puzzle where the digit "7" appears as a candidate in the following positions:
Digit 7 Candidate Distribution:
Row 2: 7 appears in cells (2,3) and (2,7)
Row 5: 7 appears in cells (5,1), (5,3), and (5,7)
Row 8: 7 appears in cells (8,1) and (8,3)
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