Sudoku technique guide

Swordfish Sudoku Technique

A Swordfish is a larger fish pattern using three rows or columns for one candidate. This guide explains the idea in plain English, when to look for it, and the common mistake to avoid.

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At a glance

Difficulty

Hard

This is where Swordfish normally sits in a human solving path.

Family

Fish techniques

It belongs to the fish techniques group of Sudoku logic.

Main action

Usually remove candidates

Most technique moves reduce notes first. That often reveals a simpler placement afterwards.

What is Swordfish?

A Swordfish is a larger fish pattern using three rows or columns for one candidate.

The important thing is that this is logic, not guessing. You are using the current candidates to prove that a number must either go in one place, or cannot stay in another place.

In SudoSketch, this technique is designed to work with notes and Coach highlighting, so the key cells and removal cells can be shown clearly.

How Swordfish works

Focus on one candidate only.
Find three rows or columns where that candidate is restricted to three matching lines.
Remove the candidate from other cells in those crossing lines.

When to look for it

Look for Swordfish after easier moves have stopped working. First check for naked singles, hidden singles, locked candidates and simple pairs. If those do not move the puzzle forward, this technique may be worth checking.

For learning, do not try to scan for every advanced technique at once. Pick one method, understand the shape, and practise spotting that one pattern.

Common mistake

Check the candidate is restricted to the same three crossing lines. Swordfish mistakes are easy when notes are incomplete.

If you are unsure, rebuild the candidates first. Bad notes create bad logic, and Sudoku will absolutely punish you for it like a tiny spreadsheet goblin.

Swordfish FAQ

What is Swordfish in Sudoku?