The technique map
Sudoku technique map
A map of the main families of standard 9 × 9 Sudoku reasoning. Follow a learning path, compare ideas, or jump into an available guide.
A useful starting path
55 techniques shown.
Read the position
Understand a unit, its peers and the difference between a candidate and a proven answer.
- Open guide →
- Open guide →
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Place a digit
Either one cell has only one choice, or one digit has only one place in a unit.
Connect a box and a line
Confined positions let you eliminate candidates across an intersection.
Reserve cells and digits
Naked subsets look at cells. Hidden subsets look at positions for digits.
- Open guide →
- Open guide →
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Track one digit across units
Fish relate sets of candidate positions across rows and columns; advanced variants add further structure.
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Connect small candidate sets
Wings use linked possibilities to identify a candidate that cannot survive.
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Recognise single-digit patterns
These patterns provide approachable examples of linked candidate reasoning.
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Follow implications
Learn strong and weak links, then follow how one candidate implies another.
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Combine almost-locked sets
Extend subset reasoning with links between sets. This branch needs careful candidate bookkeeping.
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Reason with a uniqueness premise
These techniques have an extra premise: the puzzle must have a unique solution. Do not assume this for arbitrary input.
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Explore further methods
A reference branch for advanced reasoning and computational approaches, not a claim of current game support.
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Distinguish a mistake from a limit
A duplicate, a puzzle with no solution, multiple solutions and a stalled logical path are different conditions.
Related research
Where singles stop working in our 512-puzzle catalog →See how a locked-candidates deduction helps solve the first Hard puzzle in our catalog.
References
HoDoKu and SudokuWiki