About Sliding Puzzle
The sliding puzzle is a 4 x 4 frame holding fifteen numbered tiles and one empty space. You slide tiles into the gap one at a time until the numbers read 1 to 15 in order, left to right and top to bottom, with the gap in the bottom-right corner.
How to play
- Only a tile directly next to the gap (above, below, left or right) can move, and it moves into the gap.
- The goal is the order 1, 2, 3, 4 on the top row through 13, 14, 15 and the gap on the bottom row.
- Each slide counts as one move. Tiles that are already in their final position are highlighted in blue.
- Every shuffle is made by taking 300 random legal moves from the solved position, so every puzzle can be solved.
- Solving the puzzle scores 1000 minus the number of moves you used, with a minimum of 1.
Controls
- Mouse or touch: tap or click any tile next to the gap to slide it.
- Keyboard: the arrow keys or W, A, S and D slide a tile in that direction into the gap. Pressing left moves the tile to the right of the gap leftwards.
- Touch: swiping on the board works the same way as the arrow keys.
- The Shuffle button starts a fresh puzzle and resets the move counter.
Tips and strategy
- Solve the top row first, then the second row. Once those eight tiles are fixed, you never need to touch them again.
- Place the last two tiles of a row together. For the top row, park 4 where 3 belongs with 3 directly below it, then swing the gap around so both slide into place, rather than placing 3 first.
- With two rows left, solve the remaining puzzle column by column from the left: 9 and 13 together, then 10 and 14, then finish 11, 12 and 15 by cycling them around the last 2 x 2 block.
- Think of moving the gap rather than the tiles. Plan the route the gap must take around a tile to push it where you want.
- Watch the blue highlights to check progress, but do not be afraid to move a correct tile temporarily if that is the only way through.
Background
The 15 puzzle was invented in the 1870s and is usually credited to Noyes Chapman, a postmaster in New York State. It became a craze in 1880 in the United States and Europe. The puzzle maker Sam Loyd later claimed to have invented it and promoted an impossible version with 14 and 15 swapped; mathematicians had already shown that exactly half of all possible arrangements cannot be solved, which is why this game only shuffles by making legal moves.
Questions
- Is every puzzle solvable?
- Yes. The board is scrambled by sliding tiles from the solved position, so the solution always exists.
- How is my score worked out?
- You get 1000 points minus your move count when you solve it. Fewer moves means a higher score, and your best is kept in your browser's local storage.