How to play sudoku
The grid has nine rows, nine columns and nine 3×3 boxes. Fill the empty cells so that every row, column and box holds each digit from 1 to 9 exactly once. Tap a cell, then tap a number on the pad. On a keyboard, type 1–9 to fill, use the arrow keys to move, Backspace to erase, N to switch notes on or off and Ctrl+Z to undo.
Difficulty levels
Easy puzzles can be solved with singles alone: find a cell with only one possible digit, or a digit with only one possible place in a row, column or box. Medium puzzles give fewer clues. Hard puzzles need techniques such as pointing pairs and naked pairs, and Expert puzzles call for advanced patterns like X-Wings and chains.
Tips
Turn on Notes to pencil in candidates — placing a digit clears it from the notes around it. Tap a filled cell to light up every matching digit. Digits that clash turn red. Your game saves itself, so you can close the page and come back later. Best times count for games finished without hints.