M,n,k-game

Last updated

Example of a completed 11,10,5-game Tic-tac-toe 5.png
Example of a completed 11,10,5-game

An m,n,k-game is an abstract board game in which two players take turns in placing a stone of their color on an m-by-n board, the winner being the player who first gets k stones of their own color in a row, horizontally, vertically, or diagonally. [1] [2] Thus, tic-tac-toe is the 3,3,3-game and free-style gomoku is the 15,15,5-game. An m,n,k-game is also called a k-in-a-row game on an m-by-n board.

Contents

The m,n,k-games are mainly of mathematical interest. One seeks to find the game-theoretic value, the result of the game with perfect play. This is known as solving the game.

Strategy stealing argument

A standard strategy stealing argument from combinatorial game theory shows that in no m,n,k-game can there be a strategy that assures that the second player will win (a second-player winning strategy). This is because an extra stone given to either player in any position can only improve that player's chances. The strategy stealing argument assumes that the second player has a winning strategy and demonstrates a winning strategy for the first player. The first player makes an arbitrary move, to begin with. After that, the player pretends that they are the second player and adopts the second player's winning strategy. They can do this as long as the strategy doesn't call for placing a stone on the 'arbitrary' square that is already occupied. If this happens, though, they can again play an arbitrary move and continue as before with the second player's winning strategy. Since an extra stone cannot hurt them, this is a winning strategy for the first player. The contradiction implies that the original assumption is false, and the second player cannot have a winning strategy.

This argument tells nothing about whether a particular game is a draw or a win for the first player. Also, it does not actually give a strategy for the first player.

Applying results to different board sizes

A useful notion is a "weak (m,n,k) game", where k-in-a-row by the second player does not end the game with a second player win.

If weak (m,n,k) is a draw, then decreasing m or n, or increasing k will also result in a drawn game.

Conversely, if weak or normal (m,n,k) is a win, then any larger weak (m,n,k) is a win.

Note that proofs of draws using pairing strategies also prove a draw for the weak version and thus for all smaller versions.

General results

The following statements refer to the first player in the weak game, assuming that both players use an optimal strategy.

Specific results

Multidimensional variant

It is possible to consider variants played on a multidimensional board instead of a bidimensional board.

For the case of k-in-a-row where the board is an n-dimensional hypercube with all edges with length k, Hales and Jewett proved [4] that the game is a draw if k is odd and

k ≥ 3n − 1

or if k is even and

k ≥ 2n+1 − 2.

They conjecture that the game is a draw also when the number of cells is at least twice the number of lines, which happens if and only if

2 kn ≥ (k + 2)n.

See also

Related Research Articles

<i>Gomoku</i> Abstract strategy board game

Gomoku, also called Five in a Row, is an abstract strategy board game. It is traditionally played with Go pieces on a Go board. It is played using a 15×15 board while in the past a 19×19 board was standard. Because pieces are typically not moved or removed from the board, gomoku may also be played as a paper-and-pencil game. The game is known in several countries under different names.

Pente Abstract strategy board game

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 capture them by flanking them on either side. This changes the overall tactical assessments players face when compared to pure placement m,n,k games such as Gomoku.

Tic-tac-toe Paper-and-pencil game for two players

Tic-tac-toe, noughts and crosses, or Xs and Os is a paper-and-pencil game for two players who take turns marking the spaces in a three-by-three grid with X or O. The player who succeeds in placing three of their marks in a horizontal, vertical, or diagonal row is the winner. It is a solved game, with a forced draw assuming best play from both players.

<i>Hex</i> (board game) Abstract strategy board game

Hex is a two player abstract strategy board game in which players attempt to connect opposite sides of a hexagonal board. Hex was invented by mathematician and poet Piet Hein in 1942 and independently by John Nash in 1948.

Fanorona

Fanorona is a strategy board game for two players. The game is indigenous to Madagascar.

A solved game is a game whose outcome 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 information and no element of chance; solving such a game may use combinatorial game theory and/or computer assistance.

Connect Four Childrens board game

Connect Four is a two-player connection board game, in which the players choose a color and then take turns dropping colored discs 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 discs. Connect Four is a solved game. The first player can always win by playing the right moves.

Combinatorial game theory has several ways of measuring game complexity. This article describes five of them: state-space complexity, game tree size, decision complexity, game-tree complexity, and computational complexity.

<i>Renju</i> Traditional board game

Renju is a professional variant of gomoku. It was named renju by Japanese journalist Ruikou Kuroiwa (黒岩涙香) on December 6, 1899 in a Japanese newspaper Yorozu chouhou (萬朝報). The name "renju" comes from the Japanese language, and means "connected pearls" in Japanese. The game is played with black and white stones on a 15×15 gridded go board.

3D tic-tac-toe 1978 video game

3D tic-tac-toe, also known by the trade name Qubic, is an abstract strategy board game, generally for two players. It is similar in concept to traditional tic-tac-toe but is played in a cubical array of cells, usually 4x4x4. Players take turns placing their markers in blank cells in the array. The first player to achieve four of their own markers in a row wins. The winning row can be horizontal, vertical, or diagonal on a single board as in regular tic-tac-toe, or vertically in a column, or a diagonal line through four boards.

In combinatorial game theory, the strategy-stealing argument is a general argument that shows, for many two-player games, that the second player cannot have a guaranteed winning strategy. The strategy-stealing argument applies to any symmetric game in which an extra move can never be a disadvantage.

In mathematics, the axiom of determinacy is a possible axiom for set theory introduced by Jan Mycielski and Hugo Steinhaus in 1962. It refers to certain two-person topological games of length ω. AD states that every game of a certain type is determined; that is, one of the two players has a winning strategy.

Domineering

Domineering is a mathematical game that can be played on any collection of squares on a sheet of graph paper. For example, it can be played on a 6×6 square, a rectangle, an entirely irregular polyomino, or a combination of any number of such components. Two players have a collection of dominoes which they place on the grid in turn, covering up squares. One player places tiles vertically, while the other places them horizontally. As in most games in combinatorial game theory, the first player who cannot move loses.

Determinacy is a subfield of set theory, a branch of mathematics, that examines the conditions under which one or the other player of a game has a winning strategy, and the consequences of the existence of such strategies. Alternatively and similarly, "determinacy" is the property of a game whereby such a strategy exists.

Connect6 Abstract strategy board game

Connect6 introduced in 2003 by Professor I-Chen Wu at Department of Computer Science and Information Engineering, National Chiao Tung University in Taiwan, is a two-player strategy game similar to Gomoku.

First-player and second-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 the second player to move can always force a win. With perfect play, if neither side can force a win, the game is a draw.

Solving chess means finding an optimal strategy for the game of chess, that is, one by which one of the players can always force a victory, or either can force a draw. It also means more generally solving chess-like games, such as Capablanca chess and infinite chess. According to Zermelo's theorem, a determinable optimal strategy must exist for chess and chess-like games.

A Maker-Breaker game is a kind of positional game. Like most positional games, it is described by its set of positions/points/elements and its family of winning-sets. It is played by two players, called Maker and Breaker, who alternately take previously-untaken elements.

Kaplansky's game or Kaplansky's n-in-a-line is an abstract board game in which two players take turns in placing a stone of their color on an infinite lattice board, the winner being the player who first gets k stones of their own color on a line which does not have any stones of the opposite color on it. It is named after Irving Kaplansky.

In a positional game, a pairing strategy is a strategy that a player can use to guarantee victory, or at least force a draw. It is based on dividing the positions on the game-board into disjoint pairs. Whenever the opponent picks a position in a pair, the player picks the other position in the same pair.

References

  1. 1 2 J. W. H. M. Uiterwijk and H. J van der Herik, The advantage of the initiative, Information Sciences 122 (1) (2000) 43-58.
  2. 1 2 Jaap van den Herik, Jos W.H.M. Uiterwijk, Jack van Rijswijck (2002). "Games solved: Now and in the future". Artificial Intelligence.
  3. Hsu, Wei-Yuan; Ko, Chu-Ling; Hsueh, Chu-Hsuan; Wu, I-Chen (2018). "Solving 7,7,5-game and 8,8,5-game". ICGA Journal . 40 (3). Retrieved 6 November 2019.
  4. Elwyn R. Berlekamp, John Horton Conway, Richard K. Guy. "Winning ways for your mathematical plays, Volume 3", A K Peters (2003)