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Overview

Sliding Puzzle

1 player · 2-12 min per session

Rearrange the tiles by sliding them into the empty space until the numeric order is restored.

Players: 1P Session length: 2-12 min

Puzzle

Goal & Core Rules

Rearrange the tiles by sliding them into the empty space until the numeric order is restored.

The board has one empty space; only tiles adjacent to it can move into the gap.
Each move slides a tile horizontally or vertically into the empty space.
Repeat until the numbers are fully ordered from 1 to the final tile.
Fewer moves and faster time usually mean a better score.

Easy 3x3

The quickest board size for short rounds.

Normal 4x4

The classic numbered 15-puzzle layout.

Hard 5x5

An expanded board that rewards longer move planning.

Controls

Mouse

Click a tile next to the gap: slide
Top menu: new game / restart

Keyboard

Arrow keys: move the empty space

Touch

Tap: move an adjacent tile
Direction pad: move the empty space
Top menu: new game / restart

Beginner Tips

Solve row by row (or edge by edge) instead of random moves.
Keep the empty space near where you’re working to reduce wasted motion.
On 4×4+, learn a standard last-layer technique; the final two rows/columns are the real puzzle.

Advanced Tips

Use cyclic moves (3-cycles) to place tiles without disturbing solved parts too much.
Plan ahead to avoid parity traps in numbered variants (some configurations are unsolvable).
Track your move count and aim for cleaner “macro” sequences instead of micro-adjusting.

Origins & History

Sliding puzzles are a class of combination puzzles where pieces are moved by sliding along constrained routes. The famous 15 puzzle (also known as the Gem Puzzle) was “invented” by Noyes Palmer Chapman in the 1870s and became a major craze in the United States in 1880.

Timeline

1874 Noyes Palmer Chapman is said to have shown an early precursor of the 15 puzzle.
1879 Manufacturing and distribution expanded, including the ‘Gem Puzzle’ name.
1880 The 15 puzzle became a widespread craze in the U.S.

Notable People

Noyes Palmer Chapman Credited with inventing the 15 puzzle
Sam Loyd Later falsely claimed invention; popularized an unsolvable challenge variant

Sources

FAQ

Why does the last part feel hardest?

Because you must position multiple tiles while preserving what’s already solved—planning beats quick moves.

Are all starting positions solvable?

In this implementation, yes: every board is generated by legal shuffles from the solved state, so each start is solvable.

Is there an optimal strategy?

There are known methods; perfect shortest solutions relate to search/heuristics and can be computationally hard.