#Tic-Tac-Toe 井字棋游戏
#全局常量
X="X"
O="O"
EMPTY=" "
#询问是否继续
def ask_yes_no(question):
 response=None;
 while response not in("y","n"):
  response=input(question).lower()
 return response
#输入位置数字
def ask_number(question ,low,high):
 response=None
 while response not in range(low,high):
  response=int(input(question))
 return response
#询问谁先走，先走方为X,后走方为O
#函数返回计算机方，玩家的角色代号
def pieces():
 go_first=ask_yes_no("玩家你是否先走（y/n):")
 if go_first=="y":
  print("\n玩家你先走.")
  human=X
  computer=O
 else:
  print("\n计算机先走.")
  computer=X
  human=O
 return computer,human
#产生新的棋盘
def new_board():
 board=[]
 for square in range(9):
  board.append(EMPTY)
 return board
#显示棋盘
def display_board(board):
 board2=board[:]
 for i in range(len(board)):
  if board[i]==EMPTY:
   board2[i]=i
 print("\t",board2[0],"|",board2[1],"|",board2[2])
 print("\t","----------")
 print("\t",board2[3],"|",board2[4],"|",board2[5])
 print("\t", "----------")
 print("\t",board2[6],"|",board2[7],"|",board2[8],"\n")
 #产生可以合法走棋位置序列（也就是还未下过子位置）
def legal_moves(board):
 moves=[]
 for square in range(9):
  if board[square]==EMPTY:
   moves.append(square)
 return moves
 #判断输赢
def winner(board):
  # 所有赢得可能情况，例如（0,1,2）就是第一行，（0,4,8,），（2,4,6）就是对角线
 WAYS_TO_WIN=((0,1,2,),(3,4,5),(6,7,8),(0,3,6),(1,4,7),(2,5,8),(0,4,8),(2,4,6))
 for row in WAYS_TO_WIN:
  if board[row[0]]==board[row[1]]==board[row[2]]!=EMPTY:
   winner=board[row[0]]
   return winner
   #棋盘没有空位置
 if EMPTY not in board:
  return "TIE"
 return False
  #人走棋
def human_move (board,human):
 legal =legal_moves(board)
 move =None
 while move not in legal:
  move=ask_number("你走那个位置？（0-8）：",0,9)
  if move not in legal:
   print("\n此位置已经落过子了")
     #print("Fine...")
 return move
  #计算机走棋
def computer_move(board,computer ,human):
 board=board[:]
   #按优劣顺序排序的下棋走子
 BEST_MOVES=(4,0,2,6,8,1,3,5,7) #最佳下棋位置顺序表
   #如果计算机能赢，就走那个位置
 for move in legal_moves(board):
   board[move]=computer
   if winner(board)==computer:
    print("计算机下棋位置...",move)
    return move
    #取消走棋方案
   board[move]=EMPTY
   #如果玩家能赢就堵住那个位置
 for move in legal_moves(board):
   board[move]=human
   if winner(board)==human:
    print("计算机下棋位置...",move)
    return move
    #取消走棋方案
   board[move]=EMPTY
   #如果不是上面情况，也就是这一轮赢不了
   #则是从最佳下棋位置表中挑出第一个合法位置
 for move in BEST_MOVES:
  if move in legal_moves(board):
   print("计算机下棋位置....",move)
   return move
  #转换角色
def next_turn(turn):
 if turn ==X:
   return O
 else:
  return X
  #主函数
def main():
  computer,human=pieces()
  turn =X
  board=new_board()
  display_board(board)
  while not winner(board):
   if turn ==human:
    move=human_move(board,human)
    board[move]=human
   else:
    move=computer_move(board,computer,human)
    board[move]=computer
   display_board(board)
   turn=next_turn(turn) #转换角色
     #游戏结束输出输赢或和棋信息
  the_winner=winner(board)
  if the_winner==computer:
   print("计算机赢！\n")
  elif the_winner==human:
   print("玩家赢！\n")
  elif the_winner=="TIE":
   print("平局，游戏结束\n")

main()
input("按任意键退出游戏")