说明：  用递归的思想求出从迷宫起点出发可以到达的点的个数，则递归四个行走方向，走到的地方做好标记，当走不通时再统计即可，还有一个要求就是需要从文件中读取迷宫地图。递归注意结束的条件。
(With the idea of recursion, the number of points that can be reached from the starting point of maze can be calculated. Then four walking directions of recursion are used to mark the places that can be reached. When they can't walk, the statistics can be done. Another requirement is to read the maze map from the file. Recursion pays attention to the condition of the end.)