Sudoku Strategies Overview: Every Technique from Beginner to Advanced
Sudoku a Day Blog ·
Every sudoku puzzle — no matter how hard it looks — can be solved with logic alone. No guessing required. But the logic you need depends on the difficulty level. This guide maps every major strategy to the level where you will actually need it.
Read it as a reference. Start at the top and work down as your puzzles get harder.
Beginner Strategies: Easy Puzzles
Naked Singles
A naked single is a cell where only one candidate digit can go. After eliminating all the digits already present in the same row, column, and box, one number remains. Place it.
This is the foundation of all sudoku solving. Most easy puzzles can be completed entirely with naked singles.
Hidden Singles
A hidden single is a digit that can only go in one cell within a row, column, or box — even though that cell may appear to have multiple candidates. Scan each unit for digits that have only one available home.
Together, naked and hidden singles carry you through easy puzzles and most medium ones.
Intermediate Strategies: Medium Puzzles
Locked Candidates (Pointing Pairs and Box-Line Reduction)
When all the possible cells for a digit within a box fall in the same row or column, that digit cannot appear elsewhere in that row or column. This is a pointing pair (or pointing triple).
The reverse also applies: when all candidates for a digit in a row or column fall within the same box, you can eliminate that digit from the rest of the box. This is box-line reduction.
Naked Pairs
Two cells in the same unit share exactly the same two candidates. Those two digits must go in those two cells — so you can remove them from every other cell in that unit.
Naked triples and quads work on the same principle with three or four cells and candidates.
Hidden Pairs
Two digits appear as candidates in exactly the same two cells within a unit, and nowhere else in that unit. Those two cells must contain those two digits — remove all other candidates from them.
Like naked pairs, this extends to hidden triples and hidden quads.
Advanced Strategies: Hard Puzzles
X-Wing
When a digit appears as a candidate in exactly two cells in each of two rows, and both rows share the same two columns, you have an X-Wing. That digit must occupy one of the two columns. Remove it from all other cells in those columns.
X-Wing also works across columns (rows become the constraint instead).
Swordfish
Swordfish extends X-Wing to three rows and three columns. When a digit is confined to two or three cells in each of three rows, and those cells all share the same three columns, eliminate the digit from all other cells in those three columns.
Hidden Singles in a Chain (Simple Coloring)
Simple coloring applies when a digit forms a chain of linked pairs across the grid. Each link alternates between two possible states. If two cells of the same color are in the same unit, that color must be wrong — eliminate it everywhere.
Expert and Master Strategies
XY-Wing
An XY-Wing uses three cells. A pivot cell has two candidates (XY). Two wing cells share one candidate each with the pivot (XZ and YZ). Any cell that sees both wings cannot contain Z — eliminate it.
XY-Wing is one of the most useful techniques at expert level.
Jellyfish
Jellyfish is a four-row (or four-column) version of Swordfish. When a digit is confined to two, three, or four cells in each of four rows, and those cells cover only four columns, eliminate the digit from all other cells in those four columns.
Forcing Chains and Advanced Chains
At master level, chains of linked bi-value cells and bi-location candidates drive eliminations that no simple pattern can explain. These include AICs (Alternating Inference Chains), which generalize coloring and X-Wings into a single framework.
If you can follow a chain and reason about its implications in both directions, you can solve almost any published sudoku without guessing.
How to Use This Guide
You do not need to learn all of these at once. Start with naked and hidden singles. When easy puzzles feel automatic, move to locked candidates and naked pairs. Move to X-Wing only when medium and hard puzzles stop yielding to the basics.
Each technique you add to your toolkit makes the next level of puzzle accessible.
Browse the full strategy guide for step-by-step examples of every technique listed here, or try today's puzzle and see how many you can apply.
Frequently Asked Questions
What is the first sudoku strategy beginners should learn?
Start with naked singles — cells where only one candidate digit can go. Once you can spot these reliably, move to hidden singles, where a digit has only one valid cell in a row, column, or box. These two techniques alone solve most easy and many medium puzzles.
What is the difference between naked pairs and hidden pairs in sudoku?
A naked pair is two cells in the same unit that share exactly the same two candidates. You can eliminate those two digits from all other cells in that unit. A hidden pair is two cells that are the only cells in a unit where two specific digits can go — you can remove any other candidates from those two cells.
When should I use X-Wing in sudoku?
Use X-Wing when a single digit appears as a candidate in exactly two cells in each of two different rows, and those cells line up in the same two columns (or vice versa). The digit must go in one of the two columns, so you can safely eliminate it from every other cell in those columns.