Solve Tic Tac Toe with Constraint satisfaction problem (CSP)

Question

I am solving tic tac toe board game with CSP. To formulate the game as a CSP, I found variables and Domain. variables are the squares in 3 by 3 game board and Domain should be X and O, in my case 1 and 2. Suppose AI is 2 and I am 1. The constraints should be the rules of the game, such as the fact that each position can only have one value and my question is what are other constraints And How do I do the backtracking?

This is my code so far

PLAYER_1 = 2
PLAYER_AI = 1

def print_solution(board):
    """Print Tic Tac Toe board
    """
    for i in range(3):
        for j in range(3):
            print(board[i][j], end= ' ')
            print()

def IsTerminal(board):
    # Vertical win
    for i in range(0, 3):
        if (board[0][i] != 0 and
            board[0][i] == board[1][i] and
            board[1][i] == board[2][i]):
            return board[0][i]

        # Horizontal win
        for i in range(0, 3):
            if (board[i] == [1,1,1]):
                return 1
            elif (board[i] == [2,2,2]):
                return 2

        # Main diagonal win
        if (board[0][0] != 0 and
            board[0][0] == board[1][1] and
            board[0][0] == board[2][2]):
            return board[0][0]

        # Second diagonal win
        if (board[0][2] != 0 and
            board[0][2] == board[1][1] and
            board[0][2] == board[2][0]):
            return board[0][2]
    
    # Is whole board full?
    for i in range(0, 3):
        for j in range(0, 3):
            # There's an empty field, we continue the game
            if (board[i][j] == 0):
                return None
    return 0
    

def is_valid(self, px, py, board):
    if px < 0 or px > 2 or py < 0 or py > 2:
        return False
    elif board[px][py] != 0:
        return False
    else:
        return True

def CSP(board):
    pass



def solveGame():
    board = [
        [0,0,0],
        [0,0,0],
        [0,0,0]
        ]
    if Current_player == 2:
        while(True):
            px = int(input('Insert the X coordinate: '))
            py = int(input('Insert the Y coordinate: '))
            if is_valid(px, py):
                board[px][py] = 2
                Current_player = 1
                break
            else:
                print('The move is not valid! Try again.')

In CSP function I have to use the backtracking. So every time it will check if the move is safe. I mean if the move does not satisfy one of the constraints AI will trackback. If the game ends in a tie, then it means that the CSP was not solved correctly, as there should be a unique solution that results in a win for one of the players.

Also I found a document from chegg. but I dont understand the constraints. Please help me to solve this question

Answer 1

As far as I understand your question I hope this answer should work :) Hope SO...

def CSP(board, col, row):
    if Is_board_full(board):
        return True


    for i in range(row):
        if is_valid(i , col, board):
           board[i][col] = 1

        if CSP(board, col+1, row) == True:
            return True

        board[i][col] = 1

    return False

With a new function

def Is_board_full(board):
# Is the whole board full?
for i in range(0, 3):
    for j in range(0, 3):
        # There's an empty field, we continue the game
        if (board[i][j] == 0):
            return False

return True