The Connect 4 Board CS115

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Connect Four is a variation of tic-tac-toe played on a rectangular board. Typically there are 6 rows and 7 columns, although your code will work for any number of rows and columns.

The game is played by two players, alternating turns, with each trying to place four checkers in a row vertically, horizontally, or diagonally. Because the board stands vertically and the checkers are subject to gravity, a checker may only be placed at the top of one of the currently existing columns (or it may start a new column).

The Board class—a preview

In this problem, you will need to create a class named Board that implements some of the features of the Connect Four game. The Board class will have three data members: there will be a two-dimensional list (a list of lists) containing characters to represent the game area, and a pair of variables holding the number of rows and columns on the board (6 rows and 7 columns is standard), but your Board datatype will be able to handle boards of any size. The details of the Board class appear below.

The Board class

You will probably want to store the representation of the board as a two-dimensional list/array

of characters. You should represent an empty slot by ' ', the space character. You should represent player X's checkers with an 'X' (the capital x character) and player O's checkers with an 'O' (the capital o character).

Methods required for the Board class

• __init__(self, width=7, height=6): This is a constructor for Board objects that (in addition to self) takes two named arguments, one for the number of rows and one for the number of columns. It uses the default number of columns and rows (7 and 6, respectively) in the event that the user does not specify those arguments. Inside the constructor, you should set the

values of the data members of the object, including initializing the two-dimensional array of characters to contain all ' 's (space characters). Note: It is tempting to initialize the board using the multiplication operator. For example, a 2 by 3 array of 0's could be constructed this way:

[ [' '] * 3 ] * 2. Unfortunately, this looks nice but doesn't work because Python actually creates multiple copies of the same row this way. Thus, changing an element in one row will

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change the corresponding entries in all of the rows! Instead, use a strategy analogous to the way we constructed a blank board in the game of life.

• __str__(self): This method returns a string (it does not print a string) representing

the Board object that calls it. Basically, each "checker" takes up one space, and all columns are separated by vertical bars (|). The columns are labeled at the bottom.

Here is an example of how your board should look:

||||||||

|||O||O|||

| |X|X|X|O| | |

---------------

0123456

See the example run below for more examples of what a board should look like as a game is played. Remember that __str__ returns a string but doesn't actually print anything! The symbol \n can be placed in a string and causes a newline (return to beginning of next line). Here's an example:

• foo = "I\nlike\nspam"

• foo

'I\nlike\nspam'

• print foo

I like spam

◦ allowsMove(self, col): This method should return True if the calling Board object can allow a move into column c (because there is space available). It returns False if c does not have space available or if it is not a valid column. Thus, this method should check to be sure that c is within the range from 0 to the last column and make sure that there is still room left in the column!

◦ addMove(self, col, ox): This method should add an ox checker, where ox is a variable holding a string that is either "X" or "O", into column col. Note that the code will have to find the highest row number available in the column col and put the checker in that row. The highest row number available is the highest index with a space character ' ' in the column c. Notice that

the highest row number corresponds to the lowest physical row on the board.

◦ setBoard(self, move_string): This method helps you (and us!) to test your Connect-Four Board class. Code is provided below, if you'd like to use it -- or adapt it to suit your representation of the game. But be sure to include a method that has this functionality in your class!

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• delMove(self,col): This method should do the "opposite" of addMove. That is, it should remove the top checker from the column col. If the column is empty, then delMove should do nothing. This function may not seem crucial right away, but it is very useful in the next problem in which you implement your own Connect Four AI... It's also useful if you implement "undo."

• winsFor(self, ox): This method should return True if the given checker, 'X' or 'O', held

in ox, has won the calling Board. It should return False otherwise. Important Note: you need to check if the player has won horizontally, vertically, or diagonally (and there are two different directions for a diagonal win).

• hostGame( self ) This is a method that, when called from a connect four board object, will run a loop allowing the user(s) to play a game. See below for an example user interface.

Here is our code for setBoard - please use this or something equivalent that works with your class:

def setBoard( self, moveString ):

• takes in a string of columns and places alternating checkers in those columns, starting with 'X'

For example, call b.setBoard('012345') to see 'X's and 'O's alternate on the bottom row, or b.setBoard('000000') to see them alternate in the left column.

moveString must be a string of integers

"""

nextCh = 'X' # start by playing 'X'

for colString in moveString:

col = int(colString)

if 0 <= col <= self.width:

self.addMove(col, nextCh)

if nextCh == 'X': nextCh = 'O'

else: nextCh = 'X'

Sample run of hostGame

Sample run:

• b = Board( 7, 6 )

• b.hostGame()

Welcome to Connect Four!

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||||||||

---------------

0123456

X's choice: 3

||||||||

||||X||||

---------------

0123456

O's choice: 4

||||||||

||||X|O|||

---------------

0123456

X's choice: 2

||||||||

| | |X|X|O| | |

---------------

0123456

O's choice: 4

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||||||||

|||||O|||

| | |X|X|O| | |

---------------

0123456

X's choice: 1

||||||||

|||||O|||

| |X|X|X|O| | |

---------------

0123456

O's choice: 2

||||||||

|||O||O|||

| |X|X|X|O| | |

---------------

0123456

X's choice: 0

X wins -- Congratulations!

||||||||

|||O||O|||

|X|X|X|X|O| | |

---------------

0123456