递推. 用f[n][l][r]表示n个柱子,从左面能看到l个,从右面能看到r个. 如果我们按照从小到大的顺序放置的话,放置最高的柱子后,大量状态都能递推到当前状态,很难写出递推式. 但是我们如果从小到大放置的话,高度为1的柱子放进去只会产生3种不同的情况. 1.最左面.2.中间.3.右面 在中间的哪里是无所谓的. 所以f[i][j][k]=f[i-1][j-1][k]+f[i-1][j][k-1]+(i-2)*f[i-1][l][r]. 边界条件 f[1][1][1]=1. #include<c…

Suppose you have N integers from 1 to N. We define a beautiful arrangement as an array that is constructed by these N numbers successfully if one of the following is true for the ith position (1 ≤ i ≤ N) in this array: The number at the ith position…

The 11th Zhejiang Provincial Collegiate Programming Contest is coming! As a problem setter, Edward is going to arrange the order of the problems. As we know, the arrangement will have a great effect on the result of the contest. For example, it will…

B - Problem Arrangement Time Limit:2000MS     Memory Limit:65536KB     64bit IO Format:%lld & %llu Submit Status Practice ZOJ 3777 Description The 11th Zhejiang Provincial Collegiate Programming Contest is coming! As a problem setter, Edward is going…

Given two integers n and k, you need to construct a list which contains n different positive integers ranging from 1 to n and obeys the following requirement: Suppose this list is [a1, a2, a3, ... , an], then the list [|a1 - a2|, |a2 - a3|, |a3 - a4|…

Suppose you have N integers from 1 to N. We define a beautiful arrangement as an array that is constructed by these N numbers successfully if one of the following is true for the ith position (1 ≤ i ≤ N) in this array: The number at the ith position…

Suppose you have N integers from 1 to N. We define a beautiful arrangement as an array that is constructed by these N numbers successfully if one of the following is true for the ith position (1 <= i <= N) in this array: The number at the ith positi…

题目链接:http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=3777 Time Limit: 2 Seconds      Memory Limit: 65536 KB The 11th Zhejiang Provincial Collegiate Programming Contest is coming! As a problem setter, Edward is going to arrange the order…

Fast Arrangement Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)Total Submission(s): 3995    Accepted Submission(s): 1141 Problem Description Chinese always have the railway tickets problem because of its' huge amo…

题目链接:New Year and Arbitrary Arrangement 题意: 有一个ab字符串,初始为空. 用Pa/(Pa+Pb)的概率在末尾添加字母a,有 Pb/(Pa+Pb)的概率在末尾添加字母b,当出现≥k个ab子串时立即停止添加字母,求最后期望的ab子串个数.(子串ab不要求连续) 例子:当k=1,aab含2个ab,bbabbab时不可能出现的,因为到了bbab就会停止添加字母. 题解: 期望DP DP果然是智商的分界线 orz @.@#,这题题意其实我也没看太懂,后来看了别人…