求解方法是：从入口出发，顺某个方向走，若能过去，继续；否则，沿着原路返回，换方向继续走，直到所有可能的通路都被找到为止。-Solving method is: starting from the entrance, and to conform to a direction, if in the past, continue otherwise, along the same route back, changing direction to go, until all the possibl