input: Write a python function to initialize a TicTacToe game board.
  assert game.board == [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
  assert game.x_player == 1
  assert game.o_player == -1
  assert game.empty == 0
output: def initialize_tictactoe():
      class TicTacToe:
          def __init__(self):
              self.board = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
              self.x_player = 1
              self.o_player = -1
              self.empty = 0
      
      return TicTacToe()
  
  game = initialize_tictactoe()