有老熊、小熊、老虎、小虎、老豹、小豹要过河，河边只有一条船，因船小，每船最多只能坐一个划手和一个乘客，动物中只有老熊、老虎、老豹和小熊能划船，当老兽不在时，它的小兽就要被其他老兽吃掉，请设计一个程序，让全部动物尽快过河。-There which stay, bear, tiger, tiger, leopard and old, small leopard to cross the river, the river is only one boat, due to small boat, eac