Tic-tac-toe is an instance of an m,n,k-game, where two players alternate taking turns on an *m*×*n* board until one of them gets *k* in a row.^{ [1] } Harary's generalized tic-tac-toe is an even broader generalization. The game can also be generalized as a n^{d} game.^{ [2] } The game can be generalised even further from the above variants by playing on an arbitrary hypergraph where rows are hyperedges and cells are vertices.

- Historic
- Variants in higher dimensions
- 3D Tic-tac-toe
- Misère games
- Misere Tic-tac-toe
- Notakto
- Variants with bigger boards
- Quixo
- Unrestricted n-in-a-row
- Isomorphic games
- Number Scrabble
- Word Tic-tac-toe
- Other variants
- Numerical Tic-tac-toe
- Check Lines
- Quantum tic-tac-toe
- Wild tic-tac-toe
- SOS
- Treblecross
- Revenge n-in-a-row
- Random turn tic-tac-toe
- Quick Tic-tac-toe
- Ultimate tic-tac-toe
- References

Many board games share the element of trying to be the first to get *n*-in-a-row, including three men's morris, nine men's morris, pente, gomoku, Qubic, Connect Four, Quarto, Gobblet, Order and Chaos, Toss Across, and Mojo.

**Variants of tic-tac-toe** date back several millennia.^{ [3] }

An early variation of tic-tac-toe was played in the Roman Empire, around the first century BC.^{ [4] } It was called Terni Lapilli and instead of having any number of pieces, each player only had three, thus they had to move them around to empty spaces to keep playing. The game's grid markings have been found chalked all over Rome.^{ [5] } However, according to Claudia Zaslavsky's book *Tic Tac Toe: And Other Three-In-A Row Games from Ancient Egypt to the Modern Computer*, Tic-tac-toe could be traced back to ancient Egypt.^{ [6] }^{ [7] } Another closely related ancient game is three men's morris which is also played on a simple grid and requires three pieces in a row to finish.^{ [8] }

3-dimensional tic-tac-toe on a 3×3×3 board. In this game, the first player has an easy win by playing in the centre if 2 people are playing.

One can play on a board of 4x4 squares, winning in several ways. Winning can include: 4 in a straight line, 4 in a diagonal line, 4 in a diamond, or 4 to make a square. Another variant, Qubic, is played on a 4×4×4 board; it was solved by Oren Patashnik in 1980 (the first player can force a win).^{ [9] } Higher-dimensional variations are also possible.^{ [10] }

In misère tic-tac-toe, the player wins if the opponent gets *n* in a row.^{ [11] }^{ [12] }^{ [13] }^{ [14] } This game is also known as avoidance tic tac toe,^{ [12] } toe-tac-tic,^{ [12] }^{ [15] } inverse tic tac toe,^{ [13] } or reverse tic tac toe.^{ [14] } A 3×3 game is a draw. More generally, the first player can draw or win on any board (of any dimension) whose side length is odd, by playing first in the central cell and then mirroring the opponent's moves.^{ [10] }^{ [13] }

Notakto is a misere and impartial form of tic tac toe. This means unlike in misere tic tac toe, in Notakto, both players play as the same symbol, X.^{ [16] } It also can be played on one or multiple boards.^{ [17] }

The game Quixo is played on a 5 by 5 board of cubes with two players or teams.^{ [18] } On a player's turn, they select a blank cube or a cube with their symbol on it that is at the edge of the board. If a blank cube was selected, the cube is turned to be the player's symbol (either a X or O). The game ends when one player gets 5 in a row.^{ [18] }^{ [19] }^{ [20] }^{ [21] }

Unrestricted n-in-a-row is played on an infinite tic-tac-toe board where the goal is for one player to get n in a row.^{ [2] }

The game called Amőba (amoeba) in Hungary is played on squared paper is 5-in-a-row variant. The winner of a match gets to fence in the completed game with a tight continuous line resulting a amoeba looking shape, hence the name.^{ [22] }

There is a game that is isomorphic to tic-tac-toe, but on the surface appears completely different. It is called Pick15^{ [23] } or Number Scrabble.^{ [24] } Two players in turn say a number between one and nine. A particular number may not be repeated. The game is won by the player who has said three numbers whose sum is 15.^{ [23] }^{ [25] } If all the numbers are used and no one gets three numbers that add up to 15 then the game is a draw.^{ [23] } Plotting these numbers on a 3×3 magic square shows that the game exactly corresponds with tic-tac-toe, since three numbers will be arranged in a straight line if and only if they total 15.^{ [26] }

eat | bee | less | →e | |
---|---|---|---|---|

air | bits | lip | →i | |

soda | book | lot | →o | |

↙ s | ↓ a | ↓ b | ↓ l | ↘ t |

Another isomorphic game uses a list of nine carefully chosen words, for instance "eat", "bee", "less", "air", "bits", "lip", "soda", "book", and "lot". Each player picks one word in turn and to win, a player must select three words with the same letter. The words may be plotted on a tic-tac-toe grid in such a way that a three in a row line wins.^{ [27] }

Numerical Tic Tac Toe is a variation invented by the mathematician Ronald Graham.^{ [28] } The numbers 1 to 9 are used in this game. The first player plays with the odd numbers, the second player plays with the even numbers. All numbers can be used only once. The player who puts down 15 points in a line wins (sum of 3 numbers).^{ [29] } This game can be generalized to a n × n board.^{ [29] }

In the 1970s, there was a two player game made by Tri-ang Toys & Games called * Check Lines*, in which the board consisted of eleven holes arranged in a geometrical pattern of twelve straight lines each containing three of the holes. Each player had exactly five tokens and played in turn placing one token in any of the holes. The winner was the first player whose tokens were arranged in

Quantum tic tac toe allows players to place a quantum superposition of numbers on the board, i.e. the players' moves are "superpositions" of plays in the original classical game. This variation was invented by Allan Goff of Novatia Labs.^{ [31] }

In wild tic-tac-toe, players can choose to place either X or O on each move.^{ [7] }^{ [32] }^{ [33] }^{ [34] } It can be played as a normal game where the player who makes three in a row wins or a misere game where they would lose.^{ [7] } This game is also called your-choice tic-tac-toe^{ [35] } or Devil's tic-tac-toe^{[ citation needed ]}.

In the game SOS, the players on each turn choose to play a "S" or an "O" in an empty square.^{ [36] } If a player creates the sequence, SOS vertically, horizontally or diagonally they get a point and also take another turn.^{ [37] } The player with the most points (SOSs) is the winner.^{ [36] }^{ [37] }

In Treblecross, both players play with the same symbol (a X^{ [13] } or black chip^{ [38] }). The game is played on a 1 by n board with k equal to 3.^{ [13] } The player who creates a three in a row of X's (or black chips) wins the game.^{ [13] }^{ [38] }

In revenge n-in-a-row, the player who creates a n-in-a-row wins unless the opponent can create a n-in-a-row in the next move where they lose.^{ [39] }^{ [13] }

In the game, random turn tic-tac-toe, a coin flip determines whose turn it is.^{ [7] }

In quick-tac-toe, on each turn the players can play their mark in any squares they want provided that all the marks are in the same vertical or horizontal row. The winner is the player who places the last mark.^{ [40] }

In ultimate tic-tac-toe, the board is composed of nine tic-tac-toe boards arranged in a 3-by-3 grid. Players take turns playing in the smaller tic-tac-toe boards until one of them wins in the larger tic-tac-toe board.

**Tic-tac-toe**, **noughts and crosses**, or **Xs and Os**, is a paper-and-pencil game for two players, *X* and *O*, who take turns marking the spaces in a 3×3 grid. 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.

**Nine men's morris** is a strategy board game for two players dating at least to the Roman Empire. The game is also known as **nine-man morris**, **mill**, **mills**, **the mill game**, **merels**, **merrills**, **merelles**, **marelles**, **morelles**, and **ninepenny marl** in English. The game has also been called **cowboy checkers** and is sometimes printed on the back of checkerboards. Nine men's morris is a solved game, that is, a game whose optimal strategy has been calculated. It has been shown that with perfect play from both players, the game results in a draw.

**Three men's morris** is an abstract strategy game played on a three by three board that is similar to tic-tac-toe. It is also related to six men's morris and nine men's morris. A player wins by forming a mill, that is, three of their own pieces in a row.

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.

**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 mathematics, the **Hales–Jewett theorem** is a fundamental combinatorial result of Ramsey theory named after Alfred W. Hales and Robert I. Jewett, concerning the degree to which high-dimensional objects must necessarily exhibit some combinatorial structure; it is impossible for such objects to be "completely random".

**Toss Across** is a game first introduced in 1969 by the now defunct Ideal Toy Company. The game was designed by Marvin Glass and Associates and created by Hank Kramer, Larry Reiner and Walter Moe, and is now distributed by Mattel. It is a game in which participants play tic-tac-toe by lobbing small beanbags at targets in an attempt to change the targets to their desired letter. As in traditional tic-tac-toe, the first player to get three of their letters in a row wins the game. There are other similar games to Toss Across known under different names, such as Tic Tac Throw.

**Score Four** is a "three dimensional" abstract strategy game, similar to Connect Four. It was first sold under the name "Score Four" by Funtastic in 1968. Lakeside issued 4 different versions in the 1970s. Later Hasbro sold the game as "**Connect Four Advanced**" in the UK.

**Harary's generalized tic-tac-toe** or **animal tic-tac-toe** is a generalization of the game tic-tac-toe, defining the game as a race to complete a particular polyomino on a square grid of varying size, rather than being limited to "in a row" constructions. It was devised by Frank Harary in March 1977, and is a broader definition than that of an m,n,k-game.

**Achi** is a two-player abstract strategy game from Ghana. It is also called tapatan. It is related to tic-tac-toe, but even more related to three men's morris, Nine Holes, Tant Fant, Shisima, and Dara, because pieces are moved on the board to create the 3-in-a-row. Achi is an alignment game.

**Shisima** is a two-player abstract strategy game from Kenya. It is related to tic-tac-toe, and even more so to three men's morris, Nine Holes, Achi, Tant Fant, and Dara, because pieces are moved on the board to create the 3-in-a-row. Unlike those other games, Shisima uses an octagonal board.

**Picaria** is a two-player abstract strategy game from the Zuni Native American Indians or the Pueblo Indians of the American Southwest. It is related to tic-tac-toe, but more related to three men's morris, Nine Holes, Achi, Tant Fant, and Shisima, because pieces can be moved to create the three-in-a-row. Picaria is an alignment game.

**Zillions of Games** is a commercial general game playing system developed by Jeff Mallett and Mark Lefler in 1998. The game rules are specified with S-expressions, *Zillions rule language*. It was designed to handle mostly abstract strategy board games or puzzles. After parsing the rules of the game, the system's artificial intelligence can automatically play one or more players. It treats puzzles as solitaire games and its AI can be used to solve them.

* Hip Hop Squares* is an American television game show originally hosted by Peter Rosenberg, which debuted on MTV2 on May 22, 2012. The show is a licensed format of CBS Television Distribution's

**Ultimate tic-tac-toe** is a board game composed of nine tic-tac-toe boards arranged in a 3 × 3 grid. Players take turns playing in the smaller tic-tac-toe boards until one of them wins in the larger tic-tac-toe board. Compared to traditional tic-tac-toe, strategy in this game is conceptually more difficult and has proven more challenging for computers.

**Notakto** is a tic-tac-toe variant, also known as **neutral** or **impartial tic-tac-toe**. The game is a combination of the games tic-tac-toe and Nim, played across one or several boards with both of the players playing the same piece. The game ends when all the boards contain a three-in-a-row of Xs, at which point the player to have made the last move loses the game. However, in this game, unlike tic-tac-toe, there will always be a player who wins any game of Notakto.

**Number Scrabble** is a mathematical game where players take turns to select numbers from 1 to 9 without repeating any numbers previously used, and the first player to amass a personal total of exactly 15 wins the game. The game is isomorphic to tic-tac-toe, as can be seen if the game is mapped onto a magic square.

**Wild tic-tac-toe** is a game similar to tic-tac-toe. However, in this game players can choose to place either X or O on each move. This game can also be played in its misere form where if a player creates a three-in-a-row of marks, that player loses the game.

A **n ^{d} game** (or

**Treblecross** is a degenerate tic-tac toe variant. The game is an octal game, played on a one-dimensional board and both players play using the same piece. Each player on their turn plays a piece in an unoccupied space. The game is won if a player on their turn creates a line of three pieces in a row.

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