Other noticeable solvers has been developed by Joris Witt and David White. Probably the oldest solver is Rolling Stone, developed at University of Alberta, Canada, Department of Computing Science by Andreas Junghanns and Jonathan Schaeffer. Then came the Sokoban solvers and the Sokoban optimizers.Ī solver is a program that finds a solution for a Sokoban level.Īn optimizer is a program that finds a shorter solution on the basis of a given solution. The more complex Sokoban levels are, however, out of reach even for the best automated solvers.First came the Sokoban player.

This is the method used by Rolling Stone, a Sokoban solver developed by the University of Alberta GAMES Group. Some Sokoban puzzles can be solved automatically by using a single-agent search algorithm, such as IDA, enhanced by several techniques which make use of domain-specific knowledge. Skilled human players rely mostly on heuristics they are usually able to quickly discard futile or redundant lines of play, and recognize patterns and subgoals, drastically cutting down on the amount of search. Sokoban is difficult not only due to its branching factor (which is comparable to chess), but also its enormous search tree depth some levels can be extended indefinitely, with each iteration requiring an exponentially growing number of moves and pushes. This is also interesting for artificial intelligence researchers, because solving Sokoban can be compared to the automated planning that needs to be done by a robot that moves boxes in a warehouse. Further work showed that it was significantly more difficult than NP problems it is PSPACE-complete. The problem of solving Sokoban puzzles has been proven to be NP-hard. Sokoban can be studied using the theory of computational complexity. The puzzle is solved when all boxes are at storage locations. The number of boxes is equal to the number of storage locations. Boxes may not be pushed into other boxes or walls, and they cannot be pulled. The player can also move into a box, which pushes it into the square beyond. The player is confined to the board, and may move horizontally or vertically onto empty squares (never through walls or boxes). Some floor squares contain boxes, and some floor squares are marked as storage locations. The game is played on a board of squares, where each square is a floor or a wall. Sokoban was created in 1981 by Hiroyuki Imabayashi, and published in December 1982 by Thinking Rabbit, a software house based in Takarazuka, Japan. Sokoban ('warehouse keeper') is a type of puzzle video game, in which the player pushes crates or boxes around in a warehouse, trying to get them to storage locations.

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