山科小菜鸡

Given an array of  integers , we say a set  is a prime set of the given array, if  and  is prime. BaoBao has just found an array of  integers  in his pocket. He would like to select at most  

Given a tree with n vertices, we want to add an edge between vertex 1 and vertex x, so that the sum of d(1, v) for all vertices v in the tree is minimized, where d(u, v) is the minimum number of edges...