Sliding Puzzle
PuzzleHow to play Sliding Puzzle
I see fifteen numbered tiles and one empty gap. I click or tap any tile sitting right next to the gap and it slides into the open space. My goal is to put every number back in order, from 1 in the top left down to 15, with the gap finishing in the bottom right corner.
Every shuffle I get is guaranteed solvable, so I never have to start over because of a stuck board. The game counts my moves and times me, so once I know the basics I try to beat my own move count. I press New Game whenever I want a fresh scramble.
About the Sliding Puzzle
The sliding puzzle is a genuine antique: the 15 puzzle swept America in 1880 in one of the first recorded puzzle crazes, complete with a famous prize offered by Sam Loyd for a challenge, swapping just the 14 and 15 tiles, that mathematicians later proved flatly impossible. Half of all scrambles are unreachable, and parity arguments tell you which half.
One empty square is the entire mechanism: every move slides a neighboring tile into the gap, so you are really moving the hole around the board. Solving is famously layered, top row first, then the next, until a final 2x3 region falls to a rehearsed rotation. It is the puzzle that teaches the difference between moving pieces and planning space.
Sliding puzzle technique
- Solve the top row completely, then the left column (or next row), and never disturb finished lines again.
- Place the last two tiles of each row together as a pair, hook them around the corner in one rehearsed maneuver.
- Think about where the empty square needs to be, moving the gap efficiently is the actual skill.
- Rotate tiles in small 2x2 or 2x3 cycles; almost the whole endgame is one practiced 6-tile rotation.
- If the final two tiles are swapped, restart, on this classic puzzle that scramble was unsolvable from the start (real versions only deal solvable boards).
FAQ
Why do rows get locked in from the top?
Because a finished row never needs to move again if you solve top-down: all remaining shuffling happens in the shrinking free area below. Breaking a completed row to 'help' a tile is the classic beginner loop; the layered method never requires it.
What is the trick for the end of each row?
The last two tiles of a row cannot be placed one by one, you park the second-to-last tile in the corner, stage the last tile below it, then rotate both into place as a unit. Learning that one three-move hook is the biggest single upgrade in sliding puzzles.
Is every scramble solvable?
Exactly half of all possible tile arrangements are reachable, a parity invariant proves the other half, including Sam Loyd's famous 14-15 swap, can never be solved. Digital versions like this one scramble by making legal moves from the solved state, so every board you get is honest.
How few moves can a 15 puzzle take?
Optimal solutions for typical scrambles run around 40-60 moves, and the hardest legal positions need 80. Humans solve layer by layer, which costs more moves but is reliable; chasing your personal move count down is the long-term game.
