Four In A Row

This program implements the game Four In A Row, to be played by two external programs (strategies).

The objective of the game is to place your pieces in a row of four pieces. The row can be horizontal, vertical, or diagonal.

The board is a matrix of 6 by 7 and each player chooses the column to place their piece. A piece will rest at the bottom of the board or on top of another piece.

The following is a representation of an empty board. Each . marks empty space and the top numbers mark the columns.

1 2 3 4 5 6 7
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .

There're two players: @ and O. The first player to move is @, then O. Each player places their pieces in turns. So after two turns, the board might look like as:

1 2 3 4 5 6 7
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . O . .
. . . . @ . .

where player @ placed their piece at column 5, and then player O too placed their piece in column 5.

A game ends when four pieces are placed in a row, as in

1 2 3 4 5 6 7
. . . . @ . O
. . . . @ . @
. . . . @ . O
. . O . @ . @
. . O @ O . O
. O O @ @ O @

and the game declares @ as the winner: "Player @ wins."

Protocol

To each strategy, this program feeds their standard input with the player they're playing as, as well as the state of the board. It's a single line where the first character is the player, a white space, 42 characters representing the board and a new line.

The player character is either @ or O.

A board character is either ., @, or O.

The sequence of characters on the board scans the board from top left to bottom right. So for example, the board

1 2 3 4 5 6 7
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . O . .
. . . . @ . .

will be received by player @ (the next to play) as:

@ ................................O......@..

The strategy has to read the whole line from input and send to the standard output the column, from 1 to 7, where it wants to place its piece. So, for example, if @ wants to place its piece in column 7, it sends

7

a single integer, terminated by a new line. Then the game will send to player O is the board

1 2 3 4 5 6 7
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . O . .
. . . . @ . @

as the message

O ................................O......@.@

Each strategy must read the game state and write their move in a never ending loop.

Strategy examples

The directory players/ has example strategies written in Python and Scheme (with the Scheme implementation called Guile). A strategy can be written in any programming language, as long as it respects the protocol.

Usage

To play a game, run this program (fiar.py) with two arguments, each implementing the protocol defined earlier. For example, the command

./fiar.py -v players/random_strategy.scm players/random_strategy.py

will make two random strategies face each other, and the switch -v will ensure the boards will be printed.

Common Problems

The game is frozen!

A common problem when writing a strategy happens when sending the column response: the game will freeze. This usually means that the strategy's output stream is buffered and has to be flushed.