Tic-tac-toe游戏在平局的情况下无法正常结束。

在Tic-tac-toe游戏的每个回合结束时，都要判断是否出现平局。如果出现平局，则将游戏状态设为“平局”，并立即结束游戏。以下是代码示例：

# 初始化游戏状态
PLAYING = "playing"
DRAW = "draw"
# 实现判断是否出现平局的函数
def check_draw(board):
    for row in board:
        for val in row:
            if val == "-":
                return False
    return True
# 游戏主循环
def main():
    # 初始化棋盘和游戏状态
    board = [["-" for _ in range(3)] for _ in range(3)]
    game_state = PLAYING
    # 循环进行游戏
    while game_state == PLAYING:
        # 显示棋盘并提示玩家输入
        display_board(board)
        row, col = get_player_input()
        # 在玩家输入的位置上放置棋子
        board[row][col] = "X"
        # 判断是否出现胜利
        if check_victory(board, "X"):
            game_state = "X wins"
        # 判断是否出现平局
        elif check_draw(board):
            game_state = DRAW
        else:
            # 计算电脑下一步的位置，并放置棋子
            row, col = get_computer_move(board)
            board[row][col] = "O"
            # 判断是否出现胜利
            if check_victory(board, "O"):
                game_state = "O wins"
            # 判断是否出现平局
            elif check_draw(board):
                game_state = DRAW
    # 游戏结束，显示最终结果
    display_board(board)
    if game_state == DRAW:
        print("It's a draw!")
    else:
        print(game_state)