Question

Need help with a 2D list - I'm almost there!

#Write a function called check_winner which takes

#as input a 2D list. It should return "X" if there are four

#adjacent "X" values anywhere in the list (row, column,

#diagonal); "O" if there are four adjacent "O" values

#anywhere in the list; and None if there are neither.

#

#Here are the ways Connect-4 is different from tic-tac-toe:

#

# - Connect-4 is played with 6 rows and 7 columns

# - You must have 4 in a row (or column or diagonal) to win

# - You may only place pieces in the bottom-most empty

# space in a column (e.g. you "drop" the pieces in the

# column and they fall to the first empty spot). Note,

# though, that this shouldn't affect your reasoning.

#

#We'll use "X" and "O" to represent the players, and

#None to represent empty spots.

#Assume there will be only one winner per board,

#no characters besides "X", "O", and None.

#Ignore whether the board is actually a valid game

# of Connect 4.

#

#Hints:

# - Check both kinds of diagonals, top-left to

# bottom-right and bottom-left to top-right.

# - This board is too large to check every possible place

# for a winner: there are 69 places a player could win.

# - Remember, if you put a negative index in a list,

# Python "wraps around" and checks the last value. You

# may have to control for this.

#Write your function here!

def is_list_identical(l):

return len(set(l)) <= 1

def check_winner(board):

rows = len(board)

cols = len(board[0])

# find rows containing 4 values together.

for row in board:

l = len(row)

for i in range(l-3):

if is_list_identical(row[i:i+4]):

return row[i]

# find cols containing 4 values together.

for c in range(cols):

col = [board[x][c] for x in range(rows)]

l = len(col)

for i in range(l-3):

if is_list_identical(col[i:i+4]):

return col[i]

# find primary diagonal (top left to bottom right)

for r in range(rows-3):

for c in range(cols-3):

data = [board[r+x][c+x] for x in range(4)]

if is_list_identical(data):

return data[0]

# find secondary diagonal (top right to bottom left)

for r in range(rows-3):

for c in range(cols-1, 3, -1):

data = [board[r+x][c-x] for x in range(4)]

if is_list_identical(data):

return data[0]

return None

#The code below tests your function on three Connect-4

#boards. Remember, the line breaks are not needed to create

#a 2D tuple; they're used here just for readability.

xwins = ((None, None, None, None, None, None, None),

(None, None, None, None, None, None, None),

(None, None, None, None, "X" , None, None),

(None, None, None, "X" , "O" , "O", None),

(None, "O" , "X" , "X" , "O" , "X", None),

("O" , "X" , "O" , "O" , "O" , "X" , "X"))

owins = ((None, None, None, None, None, None, None),

(None, None, None, None, None, None, None),

("O" , "O" , "O" , "O" , None, None, None),

("O" , "X" , "X" , "X" , None, None, None),

("X" , "X" , "X" , "O" , "X" , None, None),

("X" , "O" , "O" , "X" , "O" , None, None))

nowins =(("X" , "X" , None, None, None, None, None),

("O" , "O" , None, None, None, None, None),

("O" , "X" , "O" , "O" , None, "O" , "O" ),

("O" , "X" , "X" , "X" , None, "X" , "X" ),

("X" , "X" , "X" , "O" , "X" , "X" , "O" ),

("X" , "O" , "O" , "X" , "O" , "X" , "O" ))

print(check_winner(xwins))

print(check_winner(owins))

print(check_winner(nowins))

Answer 1

Program:

Output: