Sokoban

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A Sokoban puzzle being solved.

Sokoban (倉庫番, Sōko-ban, lit.'warehouse keeper'[1]) is a puzzle video game in which the player pushes boxes around in a warehouse, trying to get them to storage locations. The game was designed in 1981 by Hiroyuki Imabayashi, and first published in December 1982.

Gameplay[edit]

The warehouse is depicted as a grid of squares, each one representing either a floor section or a wall section. Some floor squares contain boxes and some are marked as storage locations. The player, often represented as a worker character, can move one square at a time horizontally or vertically onto empty floor squares, but cannot pass through walls or boxes.

To move a box, the player walks up to it and pushes it to the square beyond. Boxes cannot be pushed to squares with walls or other boxes, and they cannot be pulled. The number of boxes equals the number of storage locations. The puzzle is solved when all boxes are located on storage locations.

Challenges and Strategy[edit]

Progressing through the game often requires meticulous planning and strategic maneuvering. A single misstep, like pushing a box into a corner or blocking others, can create unsolvable scenarios, forcing the player to backtrack or restart the puzzle. Anticipating the consequences of each push, and considering the overall layout of the puzzle are crucial to avoid these deadlocks.

Selected official releases[edit]

Year Title Country Platform Publisher Media Notes
1982 Sokoban (倉庫番) Japan NEC PC-8801 Thinking Rabbit Cassette tape
1983 Sokoban [Extra Edition] (倉庫番[番外編][2][3]) Japan NEC PC-8801 PCマガジン Type-in program
1984 Sokoban 2 (倉庫番2) Japan NEC PC-8801 Thinking Rabbit Cassette tape
1986 Namida no Sokoban Special (涙の倉庫番スペシャル) Japan Famicom Disk System ASCII Corporation Floppy
1988 Soko-Ban US IBM PC, XT, and AT Spectrum HoloByte Floppy
1989 Soko-ban Perfect (倉庫番Perfect) Japan NEC PC-9801 Thinking Rabbit Floppy
1990 Boxyboy Japan, US Turbografx-16/PC Engine NEC HuCard
1990 Shove It! ...The Warehouse Game Japan, US Sega Genesis/Mega Drive Masaya Games ROM cartridge
1991 Soko-ban Revenge (倉庫番Revenge) Japan NEC PC-9801 Thinking Rabbit Floppy
2016 Sokoban Touch (倉庫番Touch) Japan, US Android and Apple iOS Thinking Rabbit Digital distribution
2018 Sokoban Smart (倉庫番スマート) Japan Windows Thinking Rabbit Digital distribution
2019 Minna No Sokoban (みんなの倉庫番) Japan Nintendo Switch and PlayStation 4 Unbalance Corporation Digital distribution
2021 The Sokoban US Nintendo Switch and PlayStation 4 Unbalance Corporation Digital distribution

Development[edit]

Sokoban was created in 1981 by Hiroyuki Imabayashi.[4][5] The first commercial game was published in December 1982 by Thinking Rabbit, a software house based in Takarazuka, Japan. Sokoban was a hit in Japan, where it sold more than 400,000 copies before being released in the United States.[6] In 1988, Sokoban was published in US by Spectrum HoloByte for the IBM PC, Commodore 64, and Apple II as Soko-Ban.[7]

Implementations[edit]

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, graphing calculators, digital cameras[8] and electronic organizers.

Scientific research[edit]

Sokoban can be studied using the theory of computational complexity. The computational problem of solving Sokoban puzzles was first proved to be NP-hard.[9][10] Further work showed that it was significantly more difficult than NP problems; it is PSPACE-complete.[11][12] This is of interest for artificial intelligence (AI) research because solving Sokoban puzzles requires planning similar to what some autonomous robots require in real-world tasks.[13][14]

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.[15] 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 search effort.

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 approach was used by Rolling Stone,[16] an early Sokoban solver developed at the University of Alberta. Festival[17] was the first automatic solver to solve all 90 levels in the widely used XSokoban test suite. However, the more complex Sokoban levels are out of reach even for the best automated solvers.[18]

Variants[edit]

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.

  • Alternative tilings: In the standard game, the mazes are laid out on a square grid. Several variants apply the rules of Sokoban to mazes laid out on other tilings. Hexoban uses regular hexagons, and Trioban uses equilateral triangles.
  • Multiple pushers: In the variant Multiban, the puzzle contains (and often requires) more than one pusher. In the game Sokoboxes Duo, strictly two characters are required to solve the puzzle, who can either take turns or work together.
  • Designated storage locations: In Sokomind Plus, some boxes and target squares are uniquely numbered. In Block-o-Mania, the boxes have different colours, and the goal is to push them onto squares with matching colours.
  • Alternative game objectives: Several variants feature different objectives from the traditional Sokoban gameplay. For instance, in Interlock and Sokolor, the boxes have different colours, but the objective is to move them so that similarly coloured boxes are adjacent. In CyberBox, each level has a designated exit square, and the objective is to reach that exit by pushing boxes, potentially more than one simultaneously. In a variant called Beanstalk, the objective is to push the elements of the level onto a target square in a fixed sequence.
  • Additional game elements: Push Crate, Sokonex, Xsok, Cyberbox and Block-o-Mania all add new elements to the basic puzzle. Examples include holes, teleports, moving blocks and one-way passages.
  • Character actions: In Pukoban, the character can pull boxes in addition to pushing them.
  • Reverse mode: The player solves the puzzle backwards, from the end to the initial position by pulling instead of pushing boxes. Standard Sokoban puzzles can be played in reverse mode, and the reverse-mode solutions can be converted to solutions for the standard-mode puzzles. Therefore, reverse-mode gameplay can also be instrumental in solving standard Sokoban puzzles.[19]

See also[edit]

External links[edit]

References[edit]

  1. ^ Yoshio Murase; Hitoshi Matsubara; Yuzuru Hiraga (1996). Norman Foo; Randy Goebel (eds.). Automatic Making of Sokoban Problems. Springer Science & Business Media. p. 592. ISBN 978-3-540-61532-3.
  2. ^ "今回はこのゲームを開発した THINKING RABBIT さんにお願いして, 市販品とは別に10の倉庫をつくってもらいましたので" [This time, we asked THINKING RABBIT, who developed this game, to build 10 warehouses separately from commercial products]. PCマガジン (in Japanese). August 1983. pp. 52–56.
  3. ^ "題して『倉庫番』PCマガジン番外編 (このプログラムは, PC-8801/9801 で使えます)" [Titled "Sokoban" PC Magazine Extra Edition (this program can be used with PC-8801 / 9801)]. PCマガジン (in Japanese). August 1983. pp. 52–56.
  4. ^ "Thinking Rabbit - 1983 Developer Interview".
  5. ^ "My conversation with Mr Hiroyuki Imabayashi".
  6. ^ Lafe Low (November 1988). "News Line; Made in Japan". inCider. p. 14.
  7. ^ Austin Barr; Calvin Chung; Aaron Williams (2021). Block Dude Puzzles are NP-Hard (and the Rugs Really Tie the Reductions Together) (PDF). CCCG (2021). p. 1.
  8. ^ "CHDK 1.5 User Manual". CHDK Wiki. Retrieved 2023-07-13.
  9. ^ Michael Fryers; Michael Greene (1995). "Sokoban" (PDF). Eureka (54): 25–32.
  10. ^ Dorit Dor; Uri Zwick (1999). "SOKOBAN and other motion planning problems". Computational Geometry. 13 (4): 215–228. doi:10.1016/S0925-7721(99)00017-6.
  11. ^ Joseph C. Culberson (1997). "Sokoban is PSPACE-complete" (PDF). Technical Report TR 97-02, Dept. of Computing Science, University of Alberta.
  12. ^ Robert Aubrey Hearn (2006). Games, Puzzles, and Computation (PDF) (PhD thesis). Massachusetts Institute of Technology. pp. 98–100.
  13. ^ Andreas Junghanns; Jonathan Schaeffer (1998). Sokoban: Evaluating standard single-agent search techniques in the presence of deadlock (PDF). p. 4.
  14. ^ Timo Virkkala (2011). Solving Sokoban (PDF) (MSc thesis). University of Helsinki. p. 1.
  15. ^ David Holland; Yaron Shoham. "Theoretical analysis on Picokosmos 17". Archived from the original on 2016-06-07.
  16. ^ Andreas Junghanns; Jonathan Schaeffer (2001). "Sokoban: Enhancing general single-agent search methods using domain knowledge". Artificial Intelligence. 129 (1–2): 219–251. doi:10.1016/S0004-3702(01)00109-6.
  17. ^ Yaron Shoham; Jonathan Shaeffer (2020). The FESS Algorithm: A Feature Based Approach to Single-Agent Search (PDF). 2020 IEEE Conference on Games (CoG). Osaka, Japan: IEEE. doi:10.1109/CoG47356.2020.9231929.
  18. ^ "Solver Statistics – Sokoban Wiki". Retrieved 8 February 2013.
  19. ^ Frank Takes (2008). "Sokoban: Reversed Solving" (PDF).