Basic Sudoku Rules
Welcome to Sudoku!
All Techniques
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Unique Solution
Many beginners think:
Pencil marks (candidates)
Candidates are simply the digits that could still fit in an empty cell.
Direct exclusion
Direct exclusion is the most reliable kind of Sudoku reasoning: pick a digit, then in a row / column / box, find the...
Box elimination
Box elimination is a very common “candidate elimination” technique.
Pairs & Subsets
Naked/Hidden pairs and subsets
Chain Basics
Strong links / weak links / alternation (AIC)
Skyscraper
Prerequisite: Chain Basics
Kite
Prerequisite: Chain Basics
X-Wing
X-Wing is a simple “rectangle” pattern for eliminating candidates: focus on one digit d .
BUG+1
Prerequisite: BUG+1 relies on the puzzle having exactly one solution .
Swordfish
Tip: Swordfish is basically an “upgraded” X-Wing .
Crane
Prerequisite: Chain Basics
Unique Rectangle (UR)
Prerequisite: UR relies on the fact that the puzzle has exactly one solution .
XY-Wing
XY-Wing (also known as Y-Wing) is a short candidate elimination chain made of one pivot and two wings .
Finned X-Wing
Recommended first: X-Wing
XYZ-Wing
XYZ-Wing is similar to XY-Wing : both use a “pivot + two wings” pattern to eliminate a shared candidate by contradict...
W-Wing
W-Wing is a short candidate elimination technique.
Empty Rectangle
Prerequisite: Chain Basics
Finned Swordfish
Prerequisite: Swordfish · Finned X-Wing
Hidden Rectangle
A Hidden Rectangle prevents the same dangerous result as a regular Unique Rectangle:
Sashimi Fish
Prerequisites: X-Wing · Finned X-Wing
Basic Coloring
Prerequisite: Chain Basics
WXYZ-Wing
If you’ve already read these, WXYZ-Wing will feel much easier: XY-Wing / XYZ-Wing
Bent Quad
A Bent Quad is also known as a generalized WXYZ-Wing.
X-Chain
Prerequisite: Chain basics
XY-Chain
Prerequisite: Chain basics
AIC (Standard Chain)
Prerequisite: Chain basics
ALS-XZ
ALS-XZ sounds abstract, but its central idea is simple:
3D Medusa (Advanced Coloring)
Prerequisite: Basic Coloring
ALS-XY-Wing
An ALS-XY-Wing joins three ALSs with two RCCs.
Grouped Chain
Prerequisite: X-Chain , AIC (Standard Chain) You’ll see this idea inside: Grouped X-Chain , Grouped AIC
Sue de Coq
Sue de Coq was originally called <strong Two-Sector Disjoint Subsets</strong .
Aligned Pair Exclusion (APE)
APE selects two blue base cells, pairs their candidates in every possible way, and rejects combinations that lead to...
Nishio Forcing Chain
Prerequisite: Chain Basics
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