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A tile-matching video game is a type of
puzzle video game Puzzle video games make up a broad genre of video games that emphasize puzzle solving. The types of puzzles can test problem-solving skills, including logic, pattern recognition, sequence solving, spatial recognition, and word completion. ...
where the player manipulates tiles in order to make them disappear according to a matching criterion. In many tile-matching games, that criterion is to place a given number of tiles of the same type so that they adjoin each other. That number is often three, and these games are called match-three games.Juul (2009) p. 100 The core challenge of tile-matching games is the identification of patterns on a seemingly chaotic board. Their origins lie in puzzle games from the 1980s such as ''
Tetris ''Tetris'' (russian: link=no, Тетрис) is a puzzle video game created by Soviet software engineer Alexey Pajitnov in 1984. It has been published by several companies for multiple platforms, most prominently during a dispute over the approp ...
'', ''
Chain Shot! is a tile-matching puzzle originally released under the name ''Chain Shot!'' in 1985 by Kuniaki Moribe (Morisuke). It has since been ported to numerous computer platforms, handheld devices, and even TiVo, with new versions as of 2016. History ...
'' (''SameGame'') and ''
Puzznic is a tile-matching puzzle video game developed and released by Taito for arcades in 1989. It was ported to the Nintendo Entertainment System, Game Boy, PC Engine, Sharp X68000, Commodore Amiga, Atari ST, Amstrad CPC, Commodore 64, MS-DOS, and ...
''. Tile-matching games were made popular in the 2000s, in the form of
casual games A casual game is a video game targeted at a mass market audience, as opposed to a hardcore game, which is targeted at hobbyist gamers. Casual games may exhibit any type of gameplay and genre. They generally involve simpler rules, shorter sessio ...
distributed or played over the Internet, notably the ''
Bejeweled ''Bejeweled'' (also referred as ''Bejeweled Deluxe'' in some releases) is a tile-matching puzzle video game by PopCap Games, developed for browsers in 2001. The first game developed by PopCap under their current name, ''Bejeweled'', involves li ...
'' series of games.Juul (2007)
/ref> They have remained popular since, with the game ''
Candy Crush Saga ''Candy Crush Saga'' is a free-to-play tile-matching video game released by King on April 12, 2012, originally for Facebook; other versions for iOS, Android, Windows Phone, and Windows 10 followed. It is a variation of their browser game ''Ca ...
'' becoming the most-played game on
Facebook Facebook is an online social media and social networking service owned by American company Meta Platforms. Founded in 2004 by Mark Zuckerberg with fellow Harvard College students and roommates Eduardo Saverin, Andrew McCollum, Dustin Mosk ...
in 2013. Tile-matching games cover a broad range of design elements, mechanics and gameplay experiences. They include purely
turn-based In video and other games, the passage of time must be handled in a way that players find fair and easy to understand. This is usually done in one of the two ways: real-time and turn-based. Real-time Real-time games have game time progress cont ...
games but may also feature
arcade Arcade most often refers to: * Arcade game, a coin-operated game machine ** Arcade cabinet, housing which holds an arcade game's hardware ** Arcade system board, a standardized printed circuit board * Amusement arcade, a place with arcade games * ...
-style
action Action may refer to: * Action (narrative), a literary mode * Action fiction, a type of genre fiction * Action game, a genre of video game Film * Action film, a genre of film * ''Action'' (1921 film), a film by John Ford * ''Action'' (1980 fil ...
elements such as time pressure, shooting or hand-eye coordination. The tile matching mechanic is also a minor feature in some larger games. Video game researcher Jesper Juul therefore considers tile matching to be a
game mechanic In tabletop games and video games, game mechanics are the rules or ludemes that govern and guide the player's actions, as well as the game's response to them. A rule is an instruction on how to play, a ludeme is an element of play like the L-sha ...
, rather than a distinct
genre Genre () is any form or type of communication in any mode (written, spoken, digital, artistic, etc.) with socially-agreed-upon conventions developed over time. In popular usage, it normally describes a category of literature, music, or other f ...
of games.Juul (2009) p. 84


History

The mechanism of matching game pieces to make them disappear is a feature of many non-digital games, including
Mahjong solitaire Mahjong solitaire (also known as Shanghai solitaire, electronic or computerized mahjong, solitaire mahjong or simply mahjong) is a single-player matching game that uses a set of mahjong tiles rather than cards. It is more commonly played on a ...
and
Solitaire Solitaire is any tabletop game which one can play by oneself, usually with cards, but also with dominoes. The term "solitaire" is also used for single-player games of concentration and skill using a set layout tiles, pegs or stones. These game ...
card games.Juul (2009) p. 98 Video game researcher Jesper Juul traces the history of tile-matching video games back to early puzzle ''
Tetris ''Tetris'' (russian: link=no, Тетрис) is a puzzle video game created by Soviet software engineer Alexey Pajitnov in 1984. It has been published by several companies for multiple platforms, most prominently during a dispute over the approp ...
'' and ''
Chain Shot! is a tile-matching puzzle originally released under the name ''Chain Shot!'' in 1985 by Kuniaki Moribe (Morisuke). It has since been ported to numerous computer platforms, handheld devices, and even TiVo, with new versions as of 2016. History ...
'' (later known as ''SameGame''), published in 1984 and 1985, respectively. While both are puzzle games, they differ in important design points such as time pressure, tile manipulation, and solving criteria. While there may have been earlier video games with tile-matching mechanics, Juul stated that the commercial success of both ''Tetris'' and ''Chain Shot!'' established the popularity of puzzle games, leading to a second generation of influential games – ''
Puzznic is a tile-matching puzzle video game developed and released by Taito for arcades in 1989. It was ported to the Nintendo Entertainment System, Game Boy, PC Engine, Sharp X68000, Commodore Amiga, Atari ST, Amstrad CPC, Commodore 64, MS-DOS, and ...
'', ''
Columns A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. ...
'', ''
Dr. Mario ''Dr. Mario'' is a 1990 puzzle video game developed and published by Nintendo for the Nintendo Entertainment System, Famicom, and Game Boy. It was produced by Gunpei Yokoi and designed by Takahiro Harada. The soundtrack was composed by Hirokaz ...
'' and '' Plotting'' – which were published in 1989 and 1990. Another early Mahjong-style pair matching game was ''
Shanghai Shanghai (; , , Standard Mandarin pronunciation: ) is one of the four direct-administered municipalities of the People's Republic of China (PRC). The city is located on the southern estuary of the Yangtze River, with the Huangpu River flowin ...
'' (1986). The popularity of the puzzle genre was further boosted when
Nintendo is a Japanese multinational video game company headquartered in Kyoto, Japan. It develops video games and video game consoles. Nintendo was founded in 1889 as by craftsman Fusajiro Yamauchi and originally produced handmade playing cards. ...
bundled the Game Boy version of ''Tetris'' with the
Game Boy The is an 8-bit fourth generation handheld game console developed and manufactured by Nintendo. It was first released in Japan on April 21, 1989, in North America later the same year, and in Europe in late 1990. It was designed by the same tea ...
handheld system upon its North American and European releases in 1989. The game helped to sell the handheld system, making it a
killer application In marketing terminology, a killer application (commonly shortened to killer app) is any computer program or software that is so necessary or desirable that it proves the core value of some larger technology, such as computer hardware, a video gam ...
, and sold over 35 million copies over the Game Boy's lifetime. As it drew in players that normally did not play video games, ''Tetris'' is considered one of the first
casual game A casual game is a video game targeted at a mass market audience, as opposed to a hardcore game, which is targeted at hobbyist gamers. Casual games may exhibit any type of gameplay and genre. They generally involve simpler rules, shorter sessio ...
s. The popularity of the late 1980s puzzle games continued to bring new titles to the market, generally building on ideas introduced in these early games. Games building on ''Dr. Marios mechanics include ''
Puyo Puyo ''Puyo Puyo'' (ぷよぷよ), previously known as ''Puyo Pop'' outside Japan, is a series of tile-matching video games created by Compile. Sega has owned the franchise since 1998, with games after 2001 being developed by Sonic Team. ''Puyo Puyo ...
'' (1991), ''
Baku Baku Animal ''Baku Baku'', released in Japan as is a falling block puzzle arcade game released by Sega in 1995. The game is dedicated as Sega's first ever Network Compatible PC Game. A Sega NetLink compatible version of the game was also announced, but n ...
'' (1995) and ''
Puzzle Fighter ''Super Puzzle Fighter II Turbo'', released in Japan as , is a tile-matching puzzle video game released in 1996 for the CP System II (CPS2) arcade board, by Capcom and its Capcom Coin-Op division. The game's title is a play on '' Super Street F ...
'' (1996). Building on the shooting mechanic introduced in ''Plotting'', ''Dr. Mario'' also influenced ''
Puzzle Bobble internationally known as ''Bust-a-Move'', is a 1994 tile-matching puzzle arcade game developed and published by Taito. It is based on the 1986 arcade game ''Bubble Bobble'', featuring characters and themes from that game. Its characteristically ...
'' (1994), which in turn inspired '' Puzz Loop'' (1998), ''
Hexic ''Hexic'' is a 2003 tile-matching puzzle video game developed by Carbonated Games for various platforms. In Hexic, the player tries to rotate hexagonal tiles to create certain patterns. The game is available on Windows, Xbox 360, Xbox One, Xbox ...
'' and '' Zuma'' (2003), and ''
Luxor Luxor ( ar, الأقصر, al-ʾuqṣur, lit=the palaces) is a modern city in Upper (southern) Egypt which includes the site of the Ancient Egyptian city of ''Thebes''. Luxor has frequently been characterized as the "world's greatest open-a ...
'' (2005). ''Columns'' was the basis of a line of development of tile matching games based on shifting or swapping tiles. It includes ''
Yoshi's Cookie ''Yoshi's Cookie'' is a 1992 tile-matching puzzle video game developed by Tose and published by Nintendo for the NES and Game Boy platforms in 1992. A Super NES version was released the following year, developed and published by Bullet-Proof So ...
'' (1992) and ''
Panel de Pon ''Tetris Attack'', also known as in Japan, is a puzzle video game developed by Intelligent Systems and published by Nintendo for the Super Nintendo Entertainment System. A Game Boy version was released a year later. In the game, the player must ar ...
'' (1995), which introduced the swapping mechanic. ''Magic Jewelry'' followed in 1990. '' Puzzled'' included multiplayer games and was released for the Neo Geo console in the same year. 1994 saw ''
BreakThru! is a tile-matching puzzle video game released for the Windows and MS-DOS in 1994. It was created by Steve Fry for the Japanese company Zoo Corporation and published by Spectrum HoloByte, for the North American market. The game would later be ...
'' and '' Gururin'' published with ''
FlipOut! ''FlipOut!'' is a tile-matching puzzle video game developed by Gorilla Systems and originally published by Atari Corporation for the Atari Jaguar in Europe on July 7, 1995 and later in North America on August 28 of the same year. It is one of the ...
'' and ''
Vid Grid ''Vid Grid'' is a Tile-matching video game, tile-matching full motion video puzzle video game, puzzle Video game, game originally developed by Geffen Records and published by Jay Samit#Jasmine Multimedia Publishing, Jasmine Multimedia Publishing f ...
'' released the following year. '' Hebereke's Popoitto'' was released in 1995 containing a two player competitive game. ''
Sega Swirl ''Sega Swirl'' is a puzzle game that was created for the Dreamcast, Personal computer and Palm OS. The game was included in various demo discs released for the Dreamcast (through the '' Official Dreamcast Magazine (UK) and Official Dreamcast Mag ...
'' for handheld devices was released in 1999. Microsoft bundled '' Jawbreaker'' Windows Mobile 2003. Several
multiplayer A multiplayer video game is a video game in which more than one person can play in the same game environment at the same time, either locally on the same computing system ( couch co-op), on different computing systems via a local area network, or ...
modes, both local and networked, featured in early tile-matching games such as ''Columns'' and ''Dr. Mario'' and later with ''
TetriNET ''TetriNET'' is a multiplayer online ''Tetris'' game for up to six people that supports team play. History Tetrinet was originally developed by St0rmCat in 1997. The last official version is 1.13. The game was originally developed for Windows a ...
'' (1997) and ''
Tetris Worlds ''Tetris Worlds'' is a version of the video game ''Tetris''. Originally released in 2001 for Microsoft Windows and Game Boy Advance, it was later released for Xbox, GameCube, and PlayStation 2 in 2002. In 2003, an Xbox Live version and a single-di ...
'' (2001). Multiplayer introduced elements of race and competition as players were able to attacks opponents in various ways resulting in more difficult matchmaking for their opponent. The first of what eventually became known as "match-three" games, where the goal is to create clusters of three or more identical items on a grid, was ''
Shariki ''Shariki'' (Russian language, Russian: Ша́рики, "The Marbles") is a puzzle video game written in 1994 for MS-DOS by Russian developer Eugene Alemzhin. The goal of the game is to gain progressively higher scores by matching three or more ...
'' (1994). It led directly to the successful ''
Bejeweled ''Bejeweled'' (also referred as ''Bejeweled Deluxe'' in some releases) is a tile-matching puzzle video game by PopCap Games, developed for browsers in 2001. The first game developed by PopCap under their current name, ''Bejeweled'', involves li ...
'' (2001), which became a series and inspired similar games including ''
Zoo Keeper A zookeeper, sometimes referred as animal keeper, is a person who manages zoo animals that are kept in captivity for conservation or to be displayed to the public.Hurwitz, Jane. Choosing a Career in Animal Care (World of Work). New York: Rosen Gr ...
'' (2003), '' Big Kahuna Reef'' (2004), '' Jewel Quest'' (2004), and '' Chuzzle'' (2005). '' Tidalis'' (2010) developed the idea further with 20 game modes and the goal of creating the longest possible chain of matching colors. Towards 2010, new trends in tile-matching games appeared. The first was driven by the popularity of mobile games. Prior to 2012, most tile-matching games had no end goal, instead challenging the player to continue as long as possible until the board reached a state where no turn was possible, or, in the case of ''Tetris'', where tiles have filled up past a given point on the board.
King King is the title given to a male monarch in a variety of contexts. The female equivalent is queen, which title is also given to the consort of a king. *In the context of prehistory, antiquity and contemporary indigenous peoples, the ti ...
, which had made similar tile-matching games for browser-based games, explored a different approach with its first mobile app, ''Bubble Witch Saga'', which had puzzle-oriented gameplay like ''Puzzle Bobble'', but applied finite restrictions on the number of moves the player could take and setting target goals such as score or clearing the board. This enabled them to create numerous levels that could be completed in a short time, making the game ideal for mobile players, and apply a
microtransaction Microtransactions, often abbreviated as mtx, are a business model where users can purchase virtual goods with micropayments. Microtransactions are often used in free-to-play games to provide a revenue source for the developers. While microtransact ...
model to provide players temporary boosts and power-ups for more difficult levels. This approach proved highly successful and King reused it for the tile-matching game ''
Candy Crush Saga ''Candy Crush Saga'' is a free-to-play tile-matching video game released by King on April 12, 2012, originally for Facebook; other versions for iOS, Android, Windows Phone, and Windows 10 followed. It is a variation of their browser game ''Ca ...
'' in 2012, itself which was inspired by ''Bejeweled''. ''Candy Crush Saga'' became one of the most financially successful
mobile game A mobile game, or smartphone game, is a video game that is typically played on a mobile phone. The term also refers to all games that are played on any portable device, including from mobile phone (feature phone or smartphone), tablet, PDA t ...
s, and established a new type of tile-matching game based on creating games broken up into levels and establishing goals to reach within a limited number of moves. This "saga" approach also extended to other genres of mobile games. The second innovation in tile-matching games was the incorporation of their mechanic into other genres. One of the first such games was '' Puzzle Quest: Challenge of the Warlords'' released in 2008. While based on a ''Bejeweled''-like tile-matching game, ''Puzzle Quest'' added elements of a
computer role-playing game A role-playing video game (commonly referred to as simply a role-playing game or RPG, as well as a computer role-playing game or CRPG) is a video game genre where the player controls the actions of a character (or several party members) immers ...
atop this. The player would take turns against a computer opponent, making matches on a common game board, with the types of tiles matched representing role-playing game elements like attacks, defense, and magic which the player used to battle their current enemy, the larger game component had the player improve their character and obtain gear that improved the value of the tiles they matched or created special effects on the tile board, such as removing all tiles of a specific type. ''Puzzle Quest'' was very popular and led to numerous games which uses the tile-matching as part of a battle system. While not directly influenced by ''Puzzle Quest'', ''
Puzzle & Dragons is a puzzle video game with Role-playing video game, role-playing and strategy games, strategy elements, developed and published by GungHo Online Entertainment for the iOS, Android (operating system), Android, and Amazon Fire platforms. ''Puzz ...
'' in 2012 was another successful mobile title that used the tile-matching part of the game for combat-related actions. Both '' Push Panic'' and ''Heroes of Kalevala'' arrived in 2010. In 2011 '' New Puzzle Bobble'' was released for iOS while '' Bubble Safari'', '' Ruby Blast'', '' Gems with Friends'' and ''
Puzzle & Dragons is a puzzle video game with Role-playing video game, role-playing and strategy games, strategy elements, developed and published by GungHo Online Entertainment for the iOS, Android (operating system), Android, and Amazon Fire platforms. ''Puzz ...
'' were first released in 2012. '' Juice Cubes'', '' Tower of Saviors'', '' Alien Hive'', ''
Marvel Puzzle Quest ''Marvel Puzzle Quest'' is a video game released by D3 Publisher and Marvel Entertainment on October 3, 2013, and developed by Demiurge Studios. The fourth installment in the '' Puzzle Quest'' series, it is a free-to-play, match-three ''Bejewele ...
'', '' Jelly Splash'' and '' Doctor Who: Legacy'' were released for mobile devices from 2013 onwards. In 2015 '' Dragon Ball Z: Dokkan Battle'', '' Ironcast'', ''
HuniePop ''HuniePop'' is a tile-matching and dating sim adult video game created by American game designer Ryan Koons, under the alias of HuniePot. The game was released for Microsoft Windows, macOS, and Linux-based personal computers in January 2015, afte ...
'', '' Hex Frvr'' and '' Sailor Moon Drops'' were all released. By 2016 millions of players were logging into titles such as '' Gardenscapes: New Acres''. The genre continues to appeal to gamers, with numerous titles including '' Boost Beast'' (2017), '' Dr. Mario World'', and '' Crystal Crisis'' (2019) among the more recent. Many casual tile matching games continue to be published. Their development is characterized by gradual evolution, where new games makes only small changes, if any, to a formula known from previous games.Juul (2009) p. 92 In the highly competitive market for downloadable casual games, new entries must be familiar enough to appeal to players of earlier games, but innovative enough to differentiate the new game from earlier ones. This leads to developers, according to Juul, "simultaneously trying to out-innovate and out-clone each other".Juul (2009) p. 94 A new style of tile-matching game arose from games like '' Triple Town'' (2010), '' 2048'' (2014), and ''
Threes ''Threes'' (stylized as ''Threes!'') is a puzzle video game by Sirvo, an independent development team consisting of game designer Asher Vollmer, illustrator Greg Wohlwend, and composer Jimmy Hinson. The game was released on February 6, 2014, f ...
'' (2014), typically called merge-style games. Here, the player either can place tiles in a limited area, or can manipulate tiles such as sliding all tiles as far as they can move in one direction. The goal is to match two, three, or more tiles of the same type, which merges those matched tiles into a single tile with a different value that then can be matched further. For example, in ''2048'', players are given random blocks with numbers 2 or 4 on them, and much match two blocks of the same number as to generate new blocks with values in the multiples of 2, with the goal to try to get a block with the value 2048 (211) or higher. While the merging mechanic had been part of other video games since as early as '' Darwin's Dilemma'' in 1990, the genre saw a boost following the success of ''Threes'' on mobile platforms.


Features

Tile-matching games that are set in a fictional background are normally based in a "bright and positive" fiction, as opposed to the warlike background of
strategy game A strategy game or strategic game is a game (e.g. a board game) in which the players' uncoerced, and often autonomous, decision-making skills have a high significance in determining the outcome. Almost all strategy games require internal decisio ...
s or the fantasy background of
massively multiplayer A massively multiplayer online game (MMOG or more commonly MMO) is an online video game with a large number of players, often hundreds or thousands, on the same server. MMOs usually feature a huge, persistent world, persistent open world, alt ...
games.Juul (2009) p. 67 Tile matching game mechanics have been combined with other mechanics to produce a great variety of puzzle game experiences. This section discusses a number of these mechanics.


Gameplay limitations

Early puzzle games like ''Tetris'' were timed – that is, new tiles are continuously added and the player is under pressure to make matches before the board fills up. The rate of tile addition often increased as to make for a more difficult challenge in longer games. Untimed (turn-based) games, in which new tiles are added only after the player has made a move, used to be the exception, although the 1985 game ''Chain Shot!'' already had an untimed mode. In untimed modes, the player is able to continue to make matches until they reach an unplayable state, in which case the game is considered over. The addition of an untimed mode to ''Bejeweled!'' was integral to that game's success, as well as one of its most important influences on subsequent games, as it made the game more accessible to less skilled players. With the introduction of ''Candy Crush Saga'', games with levels featuring limits on the number of moves were introduced. In this, the player may be challenged to achieve a certain score, or match enough tiles of a specific color before running out of turns, or otherwise would have to complete the level again.


Tile arrangement, manipulation, and matching

Tiles may be arranged on a horizontal surface or vertically (that is, stacked atop one another, and dropping down when tiles below are removed). In the latter case, some games allow moving or rotating new tiles as they fall down from the top of the playing area, as in ''Tetris'' or ''Dr. Mario''; or they may allow only the manipulation of tiles that have already fallen, as in ''Yoshi's Cookie''. ''
Panel de Pon ''Tetris Attack'', also known as in Japan, is a puzzle video game developed by Intelligent Systems and published by Nintendo for the Super Nintendo Entertainment System. A Game Boy version was released a year later. In the game, the player must ar ...
'' introduced, and ''Bejeweled'' popularized the mechanism of tile swapping, in which tiles may be moved by exchanging the position of two adjacent tiles. Another frequently used tile manipulation method is having the player shoot the tiles onto the board, such as in '' Plotting'' and its descendants including '' Zuma''. The first method, which allows only moves that create a match, results in a more strategic, thoughtful style of play, whereas the second method requires hand-eye coordination in addition to pattern recognition skills, and makes for a more hectic style of play.


Scoring

In most tile-matching games, players obtain points for each match. Higher
score Score or scorer may refer to: *Test score, the result of an exam or test Business * Score Digital, now part of Bauer Radio * Score Entertainment, a former American trading card design and manufacturing company * Score Media, a former Canadian ...
s are awarded for more difficult matches, such as those involving a greater number of similar tiles. In some tile games, when tiles are matched and removed, pieces above them fall to fill the space (as with ''Bejeweled'' and ''Candy Crush Saga''). This creates the potential for additional matches and creating scoring combos, with all subsequent matches scored at higher point values.


Victory and loss

Some games drop tiles at random, others according to
algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
s. In most tile-matching games, new tiles are randomly added to the board continuously, either turn by turn or in real time. This may continue indefinitely or for a given period of time or number of turns. The player must continuously remove the newly added tiles through matching. The game may end with a loss when the board is filled with tiles or if there are no more possible matches. It may end with a victory when the player clears the board or reaches a given score.


Significance

Among downloadable casual video games, according to a survey referred to by Juul, tile-matching games were the second most popular game type in 2004 and by far the most popular in 2005. After that, their popularity declined: they were the fourth most popular of several genres in 2006 and 2007, and in 2008 a games publisher referred to them as a "niche" genre. But as they became well known and therefore assumed to be immediately playable by many people, tile-matching games migrated to other, more ubiquitous distribution channels such as cell phones and smartphones.Juul (2009) p. 100 Despite their commercial popularity, tile-matching games are among the games with the lowest status among video game enthusiasts, to the point where reviewers have advised gamers not to be ashamed of playing them. This may be because critics consider that there are too many of these games, which differ only slightly from each other. It may also be because, as casual games, tile-matching games are designed to be easily accessible and easy to play, which conflicts with a traditional video gaming ethos that demands games to be challenging and punishing.Juul (2009) p. 85


Computational complexity

Match-three games are
NP-hard In computational complexity theory, NP-hardness ( non-deterministic polynomial-time hardness) is the defining property of a class of problems that are informally "at least as hard as the hardest problems in NP". A simple example of an NP-hard p ...
when generalized to an n \times n playfield and played such that the player knows in advance all the tiles that will appear, with no random chance involved.


Bibliography

* *


References

{{Video game genre