Tilerace
The sliding puzzle you have met before, as a race. Fifteen numbered tiles and one empty square, scrambled the same way for everybody at the table. Tap a tile in line with the gap and it slides into it, along with any tiles between them. Put the fifteen in order before the others do and the game is yours.
The rules
- Everybody gets the same scramble, on their own board. What you do to yours does not touch anybody else's.
- The game begins with a lobby: when everyone has pressed Ready a three second countdown runs, and then every board goes live at the same moment.
- Tap a tile that shares a row or a column with the empty square and it slides into it. Every tile between the two slides along with it, so one tap can move up to three tiles.
- A tap on a tile that is not in line with the empty square does nothing. Neither does a tap on the empty square itself: it is a gap, not a tile.
- The arrow keys move the gap instead, one square at a time, which is one tile moved per key.
- Your moves are counted in tiles and not in taps, because a tap that slides three tiles is three moves.
- The board ends when everybody has finished, or when the time runs out, or when the player who finished first has been waiting a while.
How a board is won
- Whoever puts the tiles in order first takes the board. Time decides it, to the millisecond.
- If nobody finishes, the board is still decided: the seats are ranked by HOW FAR FROM DONE they were, and then by how few moves they used getting there.
- How far from done is not how many tiles are in their places, and the two often disagree. A board with fourteen tiles home can be twenty moves from finished, because the last two need a long loop to put right, while a board with eight home can be six moves away. So you can end a board looking tidier than somebody else and still place behind them, and that is the honest answer rather than a flattering one.
- The figure used is a lower bound on the moves still needed. Two seats it cannot tell apart share the place, which is what not knowing should look like.
- One scramble decides it. A game is that one board, so there is no coming back from it in the next.
The speed limit, and why it is here
- The answer to a sliding puzzle is public. You know what the finished board looks like before you start, and so does everybody else, and so does any computer.
- A program can work out a perfect route for one of these in less time than it takes to read this sentence. Nothing here can stop that, and pretending otherwise would be worse than saying it.
- What there is, is a speed limit. A board finished faster than a person could tap is recorded as unrated for that seat, and everybody else's result stands. It is a nuisance to a script and not a wall, and it is the whole of the defence.
- So the leaderboard for this game is what it is. The game is the race against the person you are playing.
Worth knowing before you start
- Work in order: the top row first, then the second, then the left of what is left. Tiles you have placed are the ones you must stop disturbing.
- The last two of a row will not go in one at a time. Put the last one above where it belongs and the second to last beside it, then turn the pair in together.
- One tap can move three tiles, which is three moves and one gesture. Lining a run up is usually cheaper than three separate taps.
- There is no undo. Sliding a tile back costs the moves it costs, the same as sliding it forward.
The seed picks the scramble and is published when the game ends, so anybody can check that everyone raced the same board. Every scramble shipped here can be solved: half of all arrangements of fifteen tiles cannot be, and those are kept out before a board is ever dealt. Each one also carries the length of its best possible solution, which is how the site knows nobody has finished in fewer moves than the puzzle allows; that figure is not shown while a board is live, because it would tell you how far you still had to go.
Tilerace terms
- The gap
- The one empty square. Tiles slide into it, and it is not a tile: tapping it does nothing.
- A run
- Two or three tiles in line with the gap that slide together on one tap. It costs a move for each tile it moved.
- A move
- One tile moving one square. The count that decides a tie, and the one a perfect route is measured in.
- How far from done
- The fewest moves that could still finish the board, at best. It is what ranks the seats that did not finish, and it is not the number of tiles in their places.
- A board
- One scramble, raced by everybody at once. That board is the game.