Sudoku

Sudoku is the world’s best-known number puzzle, and it needs no arithmetic at all. A 9 × 9 grid, divided into nine 3 × 3 boxes, comes with some digits already in place. Your job is to fill in the rest so that no digit repeats in any row, column or box.

On Alex Play Zone a new Sudoku appears every two hours in one of three difficulties. Each has exactly one solution, reachable by reasoning alone.

How to start a game

1. 1Open Sudoku on Alex Play Zone; the clock starts when the puzzle opens.
2. 2Tap a cell, then a digit on the pad — or type it on a keyboard. Tap the same digit again to remove it.
3. 3Switch Notes on to pencil small candidate digits into a cell. Notes are yours alone and are never checked.
4. 4Undo steps back, Erase empties the selected cell and Hint fills one cell correctly.

The rules of Sudoku

The rule

• Every row holds each digit from 1 to 9 exactly once.
• Every column holds each digit exactly once.
• Every 3 × 3 box holds each digit exactly once.
• The digits you are given cannot be changed. A digit that repeats in its row, column or box turns red.

A new puzzle every two hours

• One new puzzle is made every two hours, and it is the same for every player.
• You get one go at each puzzle. Leave and come back whenever you like: your grid is kept and the clock only runs while the puzzle is open.
• When the next puzzle arrives, an unfinished one is closed and shows as abandoned in your Battle Log.

Rewards

• The faster you finish, the more XP and coins you earn.
• Up to 35 for an easy puzzle, 55 for a medium and 75 for a hard one.
• Each hint takes 10% off the reward. Guests can play; XP and coins need a free account.

How to play well

Start with the fullest digit

The small number under each pad button shows how many of that digit are still to be placed. A digit with only one or two left has very few places it can go.

One place in a box

Pick a digit and a box. Cross off, in your head, every row and column of that box that already contains the digit elsewhere. If one cell is left, the digit goes there.

One digit in a cell

Look at a cell’s row, column and box together. If eight different digits already appear among them, the cell must be the ninth.

Use notes, then look for pairs

When the easy steps run out, note the candidates in the emptiest boxes. Two cells in a row that can each only be the same two digits use those digits up — remove them from the rest of that row.

Remember: Look for the digit that already appears most often — the few places left for it are usually the easiest to pin down.

Common mistakes

• Guessing when stuck. A wrong digit stays hidden until it wrecks the grid much later.
• Filling in notes for the whole grid at once — it hides the easy placements under clutter.
• Not updating notes after placing a digit, then trusting a candidate that is no longer possible.

Questions and answers

Is the Sudoku the same for everyone?

Yes. Every player gets the same grid for each two-hour round.

Do hints cost anything?

Each hint reduces your reward for that puzzle by 10%.

Are my notes checked?

No. Notes are a scratch pad for you alone and are never marked right or wrong.