Sudoku solving techniques

Every technique Sudoku Knockout’s puzzles need, from your first hidden single to chains, explained with real puzzles. They’re grouped by the level that first needs them, and no puzzle ever needs a guess.

Reading the pictures
  • Rows are named A to I from the top, columns 1 to 9 from the left: B7 is row B, column 7.
  • Small digits are notes: the digits a cell can still take, at that point of the solve.
  • Blue circles mark the pattern, orange the digit or cells it’s about, and red struck-through notes are the ones it rules out.
  • Purple lines are links between notes: solid for strong links, dashed for weak ones.

Easy

No notes needed: every digit has one place left somewhere.

Hidden single

The only place left for a digit in a row, column or box.

Medium

Some cells only show themselves once you see which digits they have left.

Naked single

A cell where only one digit is left.

Hard

Notes, and the first patterns that clear them.

Locked candidates

A digit stuck on one line inside a box, or inside one box along a line.

Naked and hidden pairs

Two cells that share the same two digits, and only those.

Expert

Patterns across the board: fish, wings and skyscrapers.

X-Wing

One digit in two rows, lined up in the same two columns.

Triples and quads

Pairs with three or four cells: three cells, three digits.

Skyscraper and 2-String Kite

Two lines where a digit has two places, joined at one end.

XY-Wing

Three cells with two notes each, linked like a hinge.

Master

Bigger fish and wings, and quads.

Swordfish and Jellyfish

X-Wing with three rows and columns, or four.

XYZ-Wing

An XY-Wing whose pivot has three notes.

W-Wing

Two matching two-note cells, linked through a strong link.

Quads (on the triples page)

Pairs with three or four cells: three cells, three digits.

Extreme

Chains, and nothing harder.

Chains: X-Chain, XY-Chain and AIC

Links of notes that prove one of two ends is true.

Put it into practice

Six levels, a thousand puzzles each, and hints that show the technique when you’re stuck.

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