Puzzles
Sudoku, alone or racing friends at a table: everybody solves the same grid, each with their own digits, seeing how far the others have got. A new one whenever you like, made for you there and then.
Playing
- Three levels - gentle, moderate and tough - and a new sudoku whenever you ask for one.
- Notes for the digits you are weighing, written small in a square; check your digits when you are stuck, or reveal one.
- Alone, or at a table with friends: everybody solves the same grid with their own digits, and sees how many squares each has filled.
- One sudoku for everybody: a room's leader board where each player solves the same grid once, timed by the centre's own clock, with no check or reveal.
- Any puzzle played again by its reference; and a sudoku for visitors to try, with no account.
- On a phone, the grid laid out to the way you hold it, and zoomed and moved with your fingers.
How the computer makes them
Every sudoku is made by the centre's computer there and then, from a number of its own choosing, at the level you asked for. A full grid is made first; then digits are taken out one at a time, each kept out only while the puzzle still has exactly one solution. It is graded by the hardest piece of reasoning needed to solve it - none ever needs a guess:
- Gentle - singles alone: a square with only one digit left, or a digit with only one square left in its row, column or box. A gentle one keeps at least 35 digits.
- Moderate - also pointing (a digit in a box confined to one row or column, so it can go nowhere else on that line) and pairs (two squares of a row, column or box with the same two digits left).
- Tough - also triples and the X-wing.
The solution is worked out on the centre's server and never sent to your browser: when you check a digit or reveal one, the server answers that one question. There is no computer player to beat - just you, the grid, and anybody racing you.
The other games
Back to the centre; how to find your way around, and what it costs (nothing): frequently asked questions.