Sudoku

Rules

Goal: Complete every cell without repeating a digit in any row, column or box.

• Each row, column and outlined box must contain every digit exactly once (1–4, 1–6 or 1–9 depending on the grid).
• Grey digits are given and cannot be changed.
• Every puzzle has exactly one solution and can be solved by logic alone: no guessing is needed.

Controls

Select a cell, then type a digit or tap the number pad. Press N (or the Notes button) to pencil in candidates. Arrow keys move; Backspace clears.

Stars

One star for a solve with hints, two for a solve without hints. Three stars: no hints and no wrong digits entered. Stars and badges never depend on Premium.

Strategy guide

Singles first

Look for a cell with only one possible digit (naked single) and a digit with only one possible cell in a row, column or box (hidden single).

Use notes

From Level 4, write candidates in each cell. Most advanced techniques are patterns among candidates.

Locked candidates

If a digit in a box can only go in one row, it can be removed from that row outside the box (and the reverse).

Pairs and triples

Two cells in a unit that hold only the same two digits claim those digits: remove them from the rest of the unit.

Fish and chains

Levels 7–10 need X-Wings, Swordfish, XY-Wings and alternating chains: follow “if this is not 5, that must be 5” links until both ends point at the same elimination.