题面 有 n n n 棵树排成一排,每棵树高度为 h i ( i ∈ [ 1 , n ] ) h_i~(i\in[1,n]) hi (i∈[1,n]) ,你现在要按照一个排列 P P P 的顺序去砍树,每砍一棵树,这棵树的高度就会变成 0 0 0 ,也就是说,砍一棵树 i i i 会使得 h i → 0 h_i\rightarrow0 hi→0 .由于光头强的阻挠,你每次砍树的代价是当前这棵树相邻两棵树的高度加上这棵树的高度,即 h i − 1 + h i + h i + 1 h_{i-1}…
Permutation p is an ordered set of integers p1, p2, ..., pn, consisting of n distinct positive integers, each of them doesn't exceed n. We'll denote the i-th element of permutation p as pi. We'll call number n the size or the length of permutation…