是的，“But as we mentioned above, for some pairs of energy states, this special atom cannot transit between them directly. What's more,when its energy state changes from one to another, for example, from Ej1 to Ejw , it can only follow a unique sequence Ej1 ,Ej2 ,Ej3 ,... , Ejw . And the most interesting thing is that it can only follow another unique sequence Ejw, ...,Ej3 ,Ej2 ,Ej1 , when it transits back from Ejw to Ej1 .”读了好久才明白这句话的意思，其实就是告诉你这是一个树，不是一个图，这样的话，用树形（这里有可能是森林）DP就ko了

• Re:这题是树还是森林? (27) wuyue19 2009-11-10 19:39:29