数据结构学习中的农夫过河问题： 有一人要将自己的兔子、蔬菜、狐狸三物品运过河，但过河的船每次只能运农夫自己和一样东西，而这三种物品之间有存在一定的制约关系：兔子不能单独和狐狸或蔬菜放在一起。构造出问题模型并编程实现求解。-Data structure learning problem in the farmer across the river: one person to own a rabbit, vegetables, fox across the river three items, but you can only transport the boat across the river itself and the farmer thing, and between the three items there are some constraints with relations: the rabbit and the fox can not stand alone or vegetables together. Structure and programming model for solving problems.