一个农夫带着一只羊，一条狼和一颗白菜想从河的东岸到西岸去。河上仅有一条船。只有农夫一人会开船。假设他每次只能带一只羊，或者一条狼，或者一颗白菜过河，并且当人不在场时，狼和羊，或羊和白菜不能单独在一起，因为狼会吃羊，羊会吃白菜。试编写程序求出他带一只羊，一条狼和一颗白菜过河的所有办法。-A farmer with a sheep, a wolf and a cabbage would like to go from the eastern shore of the river to the West Bank. Only one boat on the river. Only one farmer will set sail. Suppose every time he can only bring a sheep or a wolf, or a cabbage across the river, and when the person is not present, the wolves and sheep, or sheep and cabbage can not be alone together, because the wolf will eat the sheep, the sheep will eat the cabbage. Try to write the program obtained him with a sheep, a wolf and a cabbage across the river all the way.