Frequently Asked Questions
Everything about how our Sudoku puzzles are rated, solved, and unlocked.
How is a puzzle’s difficulty scored?
Every puzzle is run through our solving engine, which cracks it the same way a person would: it tries the simplest technique that makes progress, then the next simplest, and so on, keeping track of the hardest technique it had to reach for.
A puzzle’s rating is that single hardest technique. If the grid can be finished using only Easy techniques, it’s rated Easy. The moment it can’t be completed without a Medium technique, it becomes a Medium — and the same logic pushes a puzzle up to Hard or Expert. So the label tells you the toughest move you’ll need, not just the average one.
Every puzzle we publish has exactly one solution and is fully solvable by logic. The techniques below are the complete toolkit, ordered from easiest to hardest.
Which techniques count as Easy, Medium, Hard, and Expert?
Solvable with the two most basic moves — no candidate bookkeeping required.
- Naked Single A cell has only one number left that fits — so it goes there.
- Hidden Single A number can legally go in only one cell of a row, column, or box.
Needs simple candidate elimination within a row, column, or box.
- Naked Pair Two cells in a unit share the same two candidates, so those two numbers can be removed from the other cells of that unit.
- Hidden Pair Two numbers can only fall in the same two cells, so every other candidate is cleared out of those cells.
- Locked Candidates (Pointing) Inside a box, a number is confined to a single row or column — so it is eliminated from the rest of that row or column.
- Locked Candidates (Claiming) Inside a row or column, a number is confined to a single box — so it is eliminated from the rest of that box.
Requires triples and grid-spanning patterns across multiple rows and columns.
- Naked Triple Three cells together use only three candidates, letting you remove those numbers from the rest of the unit.
- Hidden Triple Three numbers are confined to the same three cells, so other candidates in those cells are removed.
- X-Wing A number forms a rectangle across two rows and two columns, which clears it from the rest of those lines.
- Swordfish The same idea as an X-Wing, but stretched across three rows and three columns.
Demands chains, pincers, and — at the very hardest — a proven trial-and-error step.
- XY-Wing A three-cell pincer pattern removes a candidate that both pincer cells can see.
- Simple Coloring A candidate is chained through the grid and two-colored; contradictions and cells that see both colors are eliminated.
- Backtracking (Trial and Error) The last resort: try a candidate and follow the logic to confirm it leads to the one valid solution. Only the toughest puzzles need it.
Each level builds on the ones before it: a Hard puzzle may still use plenty of Easy and Medium moves — it just needs at least one Hard technique to finish.
What does a “Mixed” book contain?
Our Easy to Expert books are ordered as a journey — Easy puzzles first, then Medium, Hard, and finally Expert — so you can warm up before the toughest grids. Every puzzle still carries its own difficulty rating.
How do the free online walkthroughs work?
Every puzzle in a printed book has a complete, step-by-step walkthrough on this site. Find the 6-digit code printed inside your book, sign in at www.ligames.fun, and enter it on your My Books page to unlock the walkthroughs for every puzzle in that volume. Puzzles #1 and #2 are always free samples, no code required.
Are the puzzles guaranteed to have one answer?
Yes. Each puzzle is generated and then checked to confirm it has a single, unique solution reachable by logic alone — no guessing needed, and never more than one valid grid. Answer keys are printed in the back of every book.