Swordfish

The Swordfish strategy is an advanced Sudoku solving technique that can be incredibly effective for tackling challenging puzzles. Similar to the X-Wing strategy but involving three rows and columns instead of two, the Swordfish strategy identifies patterns where a particular candidate number can only occupy the same three columns within three rows (or vice versa). Here’s a detailed breakdown on how to use the Swordfish strategy effectively:

Understanding the Basics

The Swordfish strategy focuses on identifying a situation where a specific candidate (number) can appear only in three columns within three different rows. This pattern allows you to eliminate that candidate from other cells in those columns, significantly narrowing down your options and bringing you closer to solving the puzzle.

Step-by-Step Guide

Identify the Candidate: Select a number you want to focus on. Let’s choose the number 4 for this example.

Scan for the Pattern: Look across three rows to see if the candidate 4 can only appear in the same three columns. Alternatively, scan three columns to see if 4 can only appear in the same three rows.

Verify the Swordfish Pattern: Confirm that within those three rows (or columns), the candidate 4 appears exactly twice (or once) in each row (or column). This forms a 3x3 grid pattern that resembles the points of a swordfish.

Eliminate Other Candidates: Once the Swordfish pattern is identified, you can eliminate the number 4 from all other cells in those three columns (or rows). This step helps refine your solving strategy by reducing possibilities.