Sudoku Strategies Overview: Every Technique from Beginner to Advanced

Use this overview to choose a technique to study, from singles to advanced chains. The order is a learning suggestion, not a guarantee that every puzzle at a named difficulty needs a particular technique. Check complete, current candidates before applying an elimination.

Begin with singles

A naked single is a cell with only one remaining candidate. A hidden single is a digit with only one possible position in a row, column or box. Rescan affected units after placing either one.

Use interactions and subsets

With pointing, all candidates for one digit in a box lie on one line, allowing removal from that line outside the box. Box-line reduction reverses the direction: candidates confined to one box along a line eliminate that digit elsewhere in the box.

A naked pair consists of two cells in one unit, each with exactly the same two candidates. A hidden pair consists of two digits restricted to the same two cells in a unit. Naked subsets remove their digits from other cells; hidden subsets remove other digits from their own cells. Triples and quads generalize the counts to three and four.

Study one-digit fish

An X-Wing confines a digit in two base rows to the same two cover columns. The two placements occupy both columns, so remove that digit from those columns outside the base rows. Transpose rows and columns for the column version. Swordfish uses three base and cover lines; Jellyfish uses four.

Follow wings and strong links

An XY-Wing has a two-candidate pivot XY and two peers with exactly XZ and YZ. Whichever pivot value is true, one wing is Z; a separate cell seeing both wings loses Z.

Simple coloring alternates colors along strong links for one digit: exactly two candidate positions in a unit. If two same-colored candidates see each other, that color is false within the connected component. A candidate outside the component seeing both colors is also false.

For forcing chains and other advanced chains, verify each implication and branch. A conclusion must follow from the stated assumptions; recognizing a chain shape alone is insufficient. No short list of techniques guarantees an easy solve of every published puzzle.

Practise one explanation at a time

Choose a lesson in the full strategy directory, work through its fixed example and explain one elimination before trying another puzzle. Return to singles whenever a new placement or elimination makes them available. The difficulty guide helps you choose a challenge without treating labels as universal technique requirements.