Sudoku Zen

Controls

Tap or click a square, then tap a number on the pad. Tap Notes to write pencil marks instead, Erase to clear the marks in a square, Undo to take back a move and Hint for help. Keys: arrows move, 1 to 9 place a digit, Shift plus a digit or N for notes, Backspace or Delete erases notes, U or Ctrl+Z undoes, H asks for a hint. P or Esc pauses.

How to play Sudoku Zen

The grid has nine rows, nine columns and nine 3x3 boxes. Fill every empty square so that each row, each column and each box holds the digits 1 to 9 exactly once. Pick a square, then pick a digit. The row, column and box of the square you picked are shaded, and every copy of the digit in that square lights up, so it is easy to see where a number can still go.

A wrong digit is not written in. It counts as a mistake instead, and three mistakes end the puzzle. Turn on Notes to pencil in small candidates while you think. When you place a digit, the game removes that digit from the notes in the same row, column and box. A number on the pad shows a check once all nine copies are on the board.

Difficulty levels and the Daily puzzle

Every puzzle is made fresh, has exactly one solution and can be finished by logic alone. Easy and Medium only ever need singles, where a square has one possible digit or a digit has one possible square. Hard brings in techniques such as locked candidates and pairs, and Expert always needs more than singles.

The Daily puzzle is the same for everyone on a given day, and its difficulty changes through the week. A solved puzzle earns up to three stars, losing one for each mistake and one for going over the target time. Your best time for each level and your Daily streak are shown on the start screen.

Tips and tricks

• Start with the digit that already appears most often. Its last few spots are usually forced.
• Scan a single box for one digit at a time. If only one square can take it, that is a hidden single.
• Use notes on harder puzzles. Two squares in a box that share the same two candidates rule those digits out everywhere else in the box.
• A hint costs a short ad. It fills one square and explains why, up to three times a game, and after a third mistake you can watch one to take it back and keep going. Skip it and you get nothing, but the button stays so you can try again.