Sokoban

 is a puzzle video game genre in which the player pushes crates or boxes around in a warehouse, trying to get them to storage locations.
"Sokoban" was created in 1981 by Hiroyuki Imabayashi. The first commercial game was published in December 1982 by Thinking Rabbit, a software house based in Takarazuka, Japan.
Gameplay.
The game is played on a board of squares, where each square is a floor or a wall. Some floor squares contain boxes, and some floor squares are marked as storage locations.
The player is confined to the board and may move horizontally or vertically onto empty squares (never through walls or boxes). The player can move a box by walking up to it and push it to the square beyond. Boxes cannot be pulled, and they cannot be pushed to squares with walls or other boxes. The number of boxes equals the number of storage locations. The puzzle is solved when all boxes are placed at storage locations.
Development.
In 1988 "Sokoban" was published in US by Spectrum HoloByte for the Commodore 64, IBM-PC and Apple II series as "Soko-Ban". "Sokoban" was a hit in Japan, and had sold over 400,000 units in that country by the time Spectrum HoloByte imported it to the United States.
Implementations.
Implementations of "Sokoban" have been written for numerous computer platforms, including almost all home computer and personal computer systems. Different versions also exist for video game consoles, mobile phones, graphic calculators, digital cameras and electronic organizers.
Scientific research.
"Sokoban" can be studied using the theory of computational complexity. The problem of solving "Sokoban" puzzles was first proved to be NP-hard. Further work showed that it was significantly more difficult than NP problems; it is PSPACE-complete. This is of interest for artificial intelligence (AI) research because solving "Sokoban" can be compared to the automated planning required by some autonomous robots.
"Sokoban" is difficult not only because of its large branching factor, but also because of its large search tree depth. Some level types can even be extended indefinitely, with each iteration requiring an exponentially growing number of moves and pushes. Skilled human players rely mostly on heuristics and are usually able to quickly discard a great many futile or redundant lines of play by recognizing patterns and subgoals, thereby drastically reducing the amount of search.
Some "Sokoban" puzzles can be solved automatically by using a single-agent search algorithm, such as IDA*; enhanced by several techniques that make use of domain-specific knowledge. This is the method used by "Rolling Stone", a "Sokoban" solver developed by the University of Alberta GAMES Group. "Festival" was the first automatic solver to solve all 90 levels in the standard benchmark test suite. However, the more complex "Sokoban" levels are out of reach even for the best automated solvers.
Variants.
Several puzzles can be considered variants of the original "Sokoban" game in the sense that they all make use of a controllable character pushing boxes around in a maze.