How to play Sliding Puzzle
The board holds numbered tiles and one empty space. Your goal is to put the tiles back in order, reading left to right and top to bottom, with 1 in the top-left corner and the gap in the bottom-right corner.
Choose 3 x 3 (tiles 1 to 8) or 4 x 4 (tiles 1 to 15) from the menu. The board is shuffled by making hundreds of random legal slides from the solved position, so every puzzle you get can definitely be solved.
- Click or tap a tile next to the gap to slide it into the empty space.
- Click a tile further away in the same row or column as the gap and the whole line of tiles between them slides together. Each tile that moves counts as one move.
- With the keyboard, each arrow key pushes a tile into the gap in that direction. For example, pressing Left moves the tile to the right of the gap leftward.
- Tiles that are already in their correct position turn teal, which helps you see your progress.
The timer starts with your first move. When every tile is in place the board turns green and a summary shows your moves and time. Your fewest moves and fastest time for each size are saved in this browser. Press Shuffle to start a new puzzle.
Controls
| Desktop | Click a tile in the same row or column as the gap to slide it. After clicking the game, the arrow keys or W, A, S, D move a tile into the gap. |
|---|---|
| Mobile | Tap any tile that lines up with the empty space to slide it, along with any tiles between it and the gap. |
Tips and strategy
Solve in layers, not all at once
Trying to fix every tile at the same time leads to endless shuffling. Instead, lock in the puzzle piece by piece. On the 3 x 3 board, complete the top row first, then treat the remaining two rows as a smaller puzzle. On the 4 x 4 board, finish the top row, then the second row, and then solve the bottom two rows column by column from the left.
The last two tiles of a row
The final tiles of each row are the tricky part, because placing one pushes the other out. The standard trick is to set them up together:
- Move the last tile of the row (for example 3) into the position where the second-to-last tile belongs (the 2 spot), temporarily.
- Bring the second-to-last tile (2) directly underneath it.
- Now rotate both into place in one smooth move: slide the gap around so that 3 moves right and 2 follows it up.
Move the gap, not the tile
It helps to think about steering the empty space. To move a tile one step in a direction, first bring the gap to the far side of the tile in that direction, taking a route that avoids your finished rows, then slide the tile across.
Protect your finished work
Once a row is complete, avoid routing the gap through it. If you ever must disturb it, make sure you can restore it quickly.
Aim for fewer moves
Sliding several tiles with one click saves time but not moves, since each tile counts. To lower your move count, plan short routes for the gap and avoid undoing your previous slide. A 3 x 3 puzzle can always be solved in 31 moves or fewer, so there is plenty of room to improve on your first attempts.
About Sliding Puzzle
Sliding tile puzzles have been popular since the late nineteenth century, when the 15 puzzle, a 4 x 4 frame of fifteen numbered blocks, became a craze in the United States and Europe. Its smaller cousin, the 8 puzzle on a 3 x 3 grid, is a classic example in computer science courses on search algorithms.
Mathematicians later showed that exactly half of all possible arrangements of the tiles cannot be solved, no matter how many moves you make. That is why this version never places tiles at random: it scrambles the board only by making legal slides, so a solution always exists.
This is our own browser version of the puzzle, written for PlayNook. It runs on your device with mouse, keyboard or touch, and keeps track of your best results for each board size.
Frequently asked questions
Is every shuffle solvable?
Yes. The board is scrambled by making random legal slides from the solved position, so it can always be returned to order.
Why do tiles turn a different colour?
A tile turns teal when it is sitting in its correct final position. It is just a visual aid and does not lock the tile in place.
How are moves counted?
Every tile that slides counts as one move. If you click a tile three spaces from the gap, three tiles slide and three moves are added.
Which arrow key moves which tile?
The arrow shows the direction a tile will travel into the gap. Pressing Up slides the tile below the gap upward, pressing Right slides the tile to the left of the gap rightward, and so on.
