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A sliding puzzle, sliding block puzzle, or sliding tile puzzle is a puzzle that challenges a player to slide usually flat pieces along certain routes (usually on a board) to establish a certain end-configuration.
The fifteen puzzle is the oldest type of sliding block puzzle. It was invented by Noyes Chapman and created a puzzle craze in 1880. Sam Loyd is often wrongly credited with making sliding puzzles popular based on his false claim that he invented the fifteen puzzle.
Unlike other tour puzzles, a sliding block puzzle prohibits lifting any piece off the board. This property separates sliding puzzles from rearrangement puzzles. Hence, finding moves and the paths opened up by each move within the two-dimensional confines of the board are important parts of solving sliding block puzzles.
Sliding puzzles are essentially two-dimensional in nature, even if the sliding is facilitated by mechanically interlinked pieces (like partially encaged marbles) or three-dimensional tokens. As this example shows, some sliding puzzles are mechanical puzzles. However, the mechanical fixtures are usually not essential to these puzzles; the parts could as well be tokens on a flat board that are moved according to certain rules.
This type of puzzle has been computerized (as puzzle video games) and is available to play for free on-line from many Web pages. It is a descendant of the jigsaw puzzle in that its point is to form a picture on-screen. The last square of the puzzle is then displayed automatically once the other pieces have been lined up.
A 7x7 puzzle. This one solves to a picture, like a jigsaw puzzle.
Examples of sliding puzzles 
See also 
- Mechanical puzzles
- Combination puzzles
- Transport Puzzle
- Rush Hour
- Rubik's Cube
- RO (game) A rotational variation
- Sliding Piece Puzzles (by Edward Hordern, 1986, Oxford University Press, ISBN 0-19-853204-0) is said to be the definitive volume on this type of puzzle.
- Winning Ways (by Elwyn Ralph Berlekamp et al., 1982, Academic Press)
- The 15 Puzzle (by Jerry Slocum & Dic Sonneveld, 2006, Slocum Puzzle Foundation)
- maa.org column on Sliding-block puzzles which rebuts the claims in the Economist.
- US Patent 4872682 - sliding puzzle wrapped on Rubik's Cube