Sudoku Guides
Long-form articles on the history, mathematics, and craft of Sudoku — where the puzzle came from, why the techniques work, and how to train them deliberately. Read alongside the worked walkthroughs and the technique picker.
History & Mathematics
- The History of Sudoku: From Euler to Your Newspaper
Sudoku was not invented in Japan. Trace the puzzle from 18th-century Latin squares through Howard Garns and Dell Magazines to Nikoli, Wayne Gould, and the 2005 boom. (9 min read)
- The Mathematics of Sudoku: Counting Grids, 17 Clues, and NP-Completeness
How many Sudoku grids exist, why 17 is the magic minimum number of clues, and what it means that Sudoku is NP-complete — the real mathematics behind the puzzle. (10 min read)
Solving Skills
- The Right Order to Learn Sudoku Techniques
A practical roadmap through Sudoku solving techniques — which to learn first, why the standard order works, how long each stage takes, and how to know you are ready to move on. (8 min read)
- Cross-Hatching and Scanning: How Fast Solvers Read the Grid
Fast Sudoku solving is a set of trained eye movements. Learn cross-hatching, digit scanning, box counting, and the habits that separate quick solvers from slow ones. (8 min read)
- Pencil Marks Done Right: Candidates Without the Clutter
When to add Sudoku pencil marks, when they hurt, full-candidate versus Snyder notation, and the maintenance discipline that keeps candidates trustworthy. (8 min read)
- What Makes a Sudoku Hard? How Difficulty Ratings Actually Work
Why one paper’s "fiendish" is another’s "medium": what difficulty raters measure, why clue count barely matters, and why technique-based practice beats star ratings. (8 min read)
Techniques in Depth
- Why Naked and Hidden Subsets Work: The Pigeonhole Principle in Action
The logical proof behind Naked Pairs, Hidden Triples, and every subset technique — one pigeonhole argument, plus the duality that makes naked and hidden mirror images. (9 min read)
- X-Wing, Swordfish, Jellyfish: The Fish Family Explained
The fish techniques share one elegant cover-set argument. How X-Wing and Swordfish actually work, where the strange names came from, and why no fish bigger than a Jellyfish is ever needed. (9 min read)
- Why Every Proper Sudoku Has Exactly One Solution
What makes a Sudoku "proper", how deadly patterns break puzzles, the techniques that exploit the uniqueness promise, and why some purists refuse to use them. (9 min read)
Reference
- The Complete Sudoku Glossary
Every Sudoku term defined in one place — cells, units, and peers; candidates and bivalue cells; naked, hidden, and locked patterns; fish, chains, deadly patterns, and more. (10 min read)