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Connect Four (also known as Connect 4, Four Up, Plot Four, Find Four, Captain's Mistress, Four in a Row, Drop Four, and Gravitrips in the Soviet Union) is a two-player connection
board game Board games are tabletop games that typically use . These pieces are moved or placed on a pre-marked board (playing surface) and often include elements of table, card, role-playing, and miniatures games as well. Many board games feature a comp ...
, in which the players choose a color and then take turns dropping colored tokens into a seven-column, six-row vertically suspended grid. The pieces fall straight down, occupying the lowest available space within the column. The objective of the game is to be the first to form a horizontal, vertical, or diagonal line of four of one's own tokens. Connect Four is a
solved game A solved game is a game whose outcome (win, lose or draw) can be correctly predicted from any position, assuming that both players play perfectly. This concept is usually applied to abstract strategy games, and especially to games with full informa ...
. The first player can always win by playing the right moves. The game was first sold under the ''Connect Four'' trademark by
Milton Bradley Milton Bradley (November 8, 1836 – May 30, 1911) was an American business magnate, game pioneer and publisher, credited by many with launching the board game industry, with his eponymous enterprise, which was purchased by Hasbro in 1984, and ...
in February 1974.


Gameplay

A gameplay example (right), shows the first player starting Connect Four by dropping one of their yellow discs into the center column of an empty game board. The two players then alternate turns dropping one of their discs at a time into an unfilled column, until the second player, with red discs, achieves a diagonal four in a row, and wins the game. If the board fills up before either player achieves four in a row, then the game is a draw.


Mathematical solution

Connect Four is a two-player game with
perfect information In economics, perfect information (sometimes referred to as "no hidden information") is a feature of perfect competition. With perfect information in a market, all consumers and producers have complete and instantaneous knowledge of all market pr ...
for both sides, meaning that nothing is hidden from anyone. Connect Four also belongs to the classification of an adversarial,
zero-sum game Zero-sum game is a mathematical representation in game theory and economic theory of a situation which involves two sides, where the result is an advantage for one side and an equivalent loss for the other. In other words, player one's gain is e ...
, since a player's advantage is an opponent's disadvantage. One measure of complexity of the Connect Four game is the number of possible games board positions. For classic Connect Four played on a 7-column-wide, 6-row-high grid, there are 4,531,985,219,092 positions''Number of legal 7 X 6 Connect-Four positions after n plies''
Online Encyclopedia of Integer Sequences
for all game boards populated with 0 to 42 pieces. The game was first solved by James Dow Allen (October 1, 1988), and independently by
Victor Allis Louis Victor Allis (born 19 May 1965) is a Dutch computer scientist working in the artificial intelligence (AI) field. In his graduate work, he revealed AI solutions for Connect Four, Qubic, and Gomoku. His dissertation introduced two new game s ...
(October 16, 1988). Allis describes a knowledge-based approach,Allis, Victor
''A Knowledge-based Approach of Connect-Four''
Vrije Universiteit, October 1988
with nine strategies, as a solution for Connect Four. Allen also describes winning strategies Allen, James D.

1990
in his analysis of the game. At the time of the initial solutions for Connect Four, brute-force analysis was not deemed feasible given the game's complexity and the computer technology available at the time. Connect Four has since been solved with brute-force methods, beginning with
John Tromp John Tromp is a Dutch computer scientist. He formerly worked for Dutch Centre for Mathematics and Computer Science. Tromp discovered the number of legal states of the board game Go, and co-authored with Bill Taylor the Tromp-Taylor Rules, which ...
's work in compiling an 8-ply database (February 4, 1995). The artificial intelligence algorithms able to strongly solve Connect Four are
minimax Minimax (sometimes MinMax, MM or saddle point) is a decision rule used in artificial intelligence, decision theory, game theory, statistics, and philosophy for ''mini''mizing the possible loss for a worst case (''max''imum loss) scenario. When de ...
or
negamax Negamax search is a variant form of minimax search that relies on the zero-sum property of a two-player game. This algorithm relies on the fact that to simplify the implementation of the minimax algorithm. More precisely, the value of a position ...
, with optimizations that include
alpha-beta pruning Alphabeta is an Israeli musical group. Alphabeta or Alpha Beta may also refer to: *The Greek alphabet, from ''Alpha'' (Αα) and ''Beta'' (Ββ), the first two letters *Alpha Beta, a former chain of Californian supermarkets *Alpha and beta anomers ...
, move ordering, and
transposition table {{no footnotes, date=November 2017 A transposition table is a cache of previously seen positions, and associated evaluations, in a game tree generated by a computer game playing program. If a position recurs via a different sequence of moves, the ...
s. The code for solving Connect Four with these methods is also the basis for the FhourstonesTromp, John
''The Fhourstones Benchmark''
1992
integer performance benchmark. The solved conclusion for Connect Four is
first-player-win In combinatorial game theory, a two-player deterministic perfect information turn-based game is a first-player-win if with perfect play the first player to move can always force a win. Similarly, a game is second-player-win if with perfect play th ...
. With
perfect play A solved game is a game whose outcome (win, lose or draw) can be correctly predicted from any position, assuming that both players play perfectly. This concept is usually applied to abstract strategy games, and especially to games with full informa ...
, the first player can force a win, on or before the 41st move by starting in the middle column. The game is a theoretical draw when the first player starts in the columns adjacent to the center. For the edges of the game board, column 1 and 2 on left (or column 7 and 6 on right), the exact move-value score for first player start is loss on the 40th move, and loss on the 42nd move, respectively. In other words, by starting with the four outer columns, the first player allows the second player to force a win.


Rule variations

There are many variations of Connect Four with differing game board sizes, game pieces, and gameplay rules. Many variations are popular with game theory and artificial intelligence research, rather than with physical game boards and gameplay by persons. The most commonly-used Connect Four board size is 7 columns × 6 rows. Size variations include 5×4, 6×5, 8×7, 9×7, 10×7, 8×8, Infinite Connect-Four, and Cylinder-Infinite Connect-Four. Several versions of Hasbro's Connect Four physical gameboard make it easy to remove game pieces from the bottom one at a time. Along with traditional
gameplay Gameplay is the specific way in which players interact with a game, and in particular with video games. Gameplay is the pattern defined through the game rules, connection between player and the game, challenges and overcoming them, plot and pla ...
, this feature allows for variations of the game. Some earlier game versions also included specially-marked discs, and cardboard column extenders, for additional variations to the game.


PopOut

''PopOut'' starts the same as traditional gameplay, with an empty board and players alternating turns placing their own colored discs into the board. During each turn, a player can either add another disc from the top, or if one has any discs of their own color on the bottom row, remove (or "pop out") a disc of one's own color from the bottom. Popping a disc out from the bottom drops every disc above it down one space, changing their relationship with the rest of the board and changing the possibilities for a connection. The first player to connect four of their discs horizontally, vertically, or diagonally wins the game.


Pop 10

Before play begins, ''Pop 10'' is set up differently from the traditional game. Taking turns, each player places one of their own color discs into the slots filling up only the bottom row, then moving on to the next row until it is filled, and so forth until all rows have been filled. Gameplay works by players taking turns removing a disc of one's own color through the bottom of the board. If the disc that was removed was part of a four-disc connection at the time of its removal, the player sets it aside out of play and immediately takes another turn. If it was not part of a "connect four", then it must be placed back on the board through a slot at the top into any open space in an alternate column (whenever possible) and the turn ends, switching to the other player. The first player to set aside ten discs of their color wins the game.


Five-in-a-Row

The ''Five-in-a-Row'' variation for Connect Four is a game played on a 6 high, 9 wide grid. Two additional board columns, already filled with player pieces in an alternating pattern, are added to the left and right sides of the standard 6-by-7 game board. The game plays similarly to the original Connect Four, except players must now get five pieces in a row to win. This is still a 42-ply game since the two new columns added to the game represent twelve game pieces already played, before the start of a game.


Power Up

In this variation of Connect Four, players begin a game with one or more specially-marked "Power Checkers" game pieces, which each player may choose to play once per game. When playing a piece marked with an anvil icon, for example, the player may immediately pop out all pieces below it, leaving the anvil piece at the bottom row of the game board. Other marked game pieces include one with a wall icon, allowing a player to play a second consecutive non-winning turn with an unmarked piece; a "×2" icon, allowing for an unrestricted second turn with an unmarked piece; and a bomb icon, allowing a player to immediately pop out an opponent's piece.


Other versions

Hasbro also produces various sizes of Giant Connect Four, suitable for outdoor use. The largest is built from weather-resistant wood, and measures 120 cm in both width and height. Connect Four was released for the
Microvision The Microvision (aka Milton Bradley Microvision or MB Microvision) is the first handheld game console that used interchangeable cartridges and in that sense is reprogrammable. It was released by the Milton Bradley Company in November 1979 for a ...
video game console in 1979, developed by Robert Hoffberg. It was also released for the Texas Instruments 99/4 computer the same year. With the proliferation of mobile devices, Connect Four has regained popularity as a game that can be played quickly and against another person over an
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
connection. In 2007, Milton Bradley published Connect Four Stackers. Instead of the usual grid, the game features a board to place colored discs on. Just like standard Connect Four, the object of the game is to try get four in a row of a specific color of discs. In 2008, another board variation Hasbro published as a physical game is
Connect 4x4 Connect 4x4 (spoken as Connect Four by Four) is a three-dimensional-thinking strategy game first released in 2009 by Milton Bradley. The goal of the game is identical to that of its similarly named predecessor, Connect Four. Players take turns p ...
. This game features a two-layer vertical grid with colored discs for four players, plus blocking discs. The object of the game is also to get four in a row for a specific color of discs. A ''
SpongeBob SquarePants ''SpongeBob SquarePants'' (or simply ''SpongeBob'') is an American animated comedy television series created by marine science educator and animator Stephen Hillenburg for Nickelodeon. It chronicles the adventures of the title character a ...
'' version of the game was released in 2009 for the show's 10th anniversary. The rules are the same as the normal version; the chips have the faces of SpongeBob and Patrick on them. It was re-released in 2014, but with Patrick being replaced with Plankton. In 2013, Bay Tek Games released a Connect Four ticket redemption arcade game under license from Hasbro. There are standard and deluxe versions of the game. Two players move and drop the checkers using buttons. If only one player is playing, the player plays against the computer. Both the player that wins and the player that loses get tickets. The player that wins gets to play a bonus round where a checker is moving and the player needs to press the button at the right time to get the ticket jackpot. In 2015 Winning Moves published Connect Four Twist & Turn. This game variant features a game tower instead of the flat game grid. The tower has five rings that twist independently. Gameplay is similar to standard Connect Four where players try to get four in a row of their own colored discs. However, with Twist & Turn, players have the choice to twist a ring after they have played a piece. It adds a subtle layer of strategy to the gameplay. In 2018, Bay Tek Games released their second Connect Four arcade game, Connect 4 Hoops. Players throw basketballs into basketball hoops, and they show up as checkers on the video screen. The game can be played by two players, or by one player against the computer. Both the player that wins and the player that loses get tickets. In 2018, Hasbro released Connect 4 Shots. This version requires the players to bounce coloured balls into the grid until one player achieves four in a row.


Popular culture

*Broadcaster and writer
Stuart Maconie Stuart Maconie (born 13 August 1961) is an English radio DJ and television presenter, writer, journalist, and critic working in the field of pop music and popular culture. He is currently a presenter on BBC Radio 6 Music where, alongside Mark ...
—while working at the ''
NME ''New Musical Express'' (''NME'') is a British music, film, gaming, and culture website and brand. Founded as a newspaper in 1952, with the publication being referred to as a 'rock inkie', the NME would become a magazine that ended up as a f ...
''—started a rumour that Connect Four was invented by
David Bowie David Robert Jones (8 January 194710 January 2016), known professionally as David Bowie ( ), was an English singer-songwriter and actor. A leading figure in the music industry, he is regarded as one of the most influential musicians of the ...
, which became an
urban myth An urban legend (sometimes contemporary legend, modern legend, urban myth, or urban tale) is a genre of folklore comprising stories or fallacious claims circulated as true, especially as having happened to a "friend of a friend" or a family m ...
. *On
The Hub The Hub may refer to: Places * The Hub, Bronx, an area of the South Bronx, New York, known for its convergence of subway and bus lines * The Hub (Edinburgh), former church in Edinburgh that is now home to the Edinburgh International Festival * T ...
's game show ''Family Game Night'', there is a game under the name " Connect 4 Basketball" in which teams use colored balls. *
Nintendo is a Japanese Multinational corporation, 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 produce ...
added a version of this game called "Four-in-a-row" to their
tabletop games Tabletop games or tabletops are games that are normally played on a table or other flat surface, such as board games, card games, dice games, miniature wargames, or tile-based games. Classification according to equipment used Tabletop games c ...
compilation Compilation may refer to: *In computer programming, the translation of source code into object code by a compiler **Compilation error **Compilation unit *Product bundling, a marketing strategy used to sell multiple products *Compilation thesis M ...
named Clubhouse Games: 51 Worldwide Classics for the
Nintendo Switch The is a hybrid video game console developed by Nintendo and released worldwide in most regions on March 3, 2017. The console itself is a Tablet computer#Gaming tablet, tablet that can either be docking station, docked for use as a home video ...
. *In the video game '' A Way Out'', Vincent and Leo can play Connect Four as a
minigame A minigame (also spelled mini game and mini-game, sometimes called a subgame or microgame) is a short game often contained within another video game. A minigame contains different gameplay elements, and is often smaller or more simplistic, than th ...
.


See also

*
Score Four Score Four is a "three dimensional" abstract strategy game, similar to Connect Four (Milton Bradley, 1974). It was first sold under the name "Score Four" by Funtastic in 1968. Lakeside issued 4 different versions in the 1970s. Later Hasbro sold ...
*
Gomoku ''Gomoku'', also called ''Five in a Row'', is an abstract strategy board game. It is traditionally played with Go pieces (black and white stones) on a Go board. It is played using a 15×15 board while in the past a 19×19 board was standard. Be ...
*
Pente Pente is an abstract strategy board game for two or more players, created in 1977 by Gary Gabrel. A member of the m,n,k game family, Pente stands out for its custodial capture mechanic, which allows players to "sandwich" pairs of stones and cap ...
*
Teeko Teeko is an abstract strategy game invented by John Scarne in 1937 and rereleased in refined form in 1952 and again in the 1960s. Teeko was marketed by Scarne's company, John Scarne Games Inc.; its quirky name, he said, borrowed letters from Tic-t ...


References


External links

*
Connect Four
at
MathWorld ''MathWorld'' is an online mathematics reference work, created and largely written by Eric W. Weisstein. It is sponsored by and licensed to Wolfram Research, Inc. and was partially funded by the National Science Foundation's National Science Dig ...
*
Connect Four game solver
() {{Authority control Board games introduced in 1974 1970s toys Milton Bradley Company games Children's board games Paper-and-pencil games Connection games Abstract strategy games Solved games Games played on Go boards Computer-assisted proofs