D. Two Paths 题目连接: http://codeforces.com/contest/14/problem/D Description As you know, Bob's brother lives in Flatland. In Flatland there are n cities, connected by n - 1 two-way roads. The cities are numbered from 1 to n. You can get from one city t…

首先有朴素的\(O(n^2)\)想法 首先枚举断边,之后对于断边之后的两棵子树求出直径 考虑优化这个朴素的想法 考虑换根\(dp\) 具体而言,首先求出\(f[i], fs[i]\)表示\(i\)号点向下的最长链以及\(i\)号子树内部最长的直径 并且在求出\(g[i]\)表示\(fa[i]\)在\(i\)号节点子树外的最长链 \(gs[i]\)表示\(i\)号节点子树外的直径 对于所有的\(fs[i] * gs[i]\)取\(max\)即为答案 首先一遍\(dfs\)把\(f, fs\)求出来…

题目地址 题意 给你一颗树 初始点颜色全部为白色 对于每一个满足要求一的点集s f(s)的定义为先把点集内的点染黑 满足要求二的路径集合数量 要求一为两两黑点之间不能出现白色的点 要求二为将这个路径集合上所有点染红(起始不能为黑色) 染红后使得每个初始染黑的点相邻的点为红或黑色 例如样例 2 1 2 2 3 选1这个点集的话 我们可以选择 {2-2},{2-3},{2-2,3-3},{2-3,2-2},{2-3,3-3},{2-3,2-2,3-3}这六种路径集 则f({1})=6 题目要求你求出…

Two Paths time limit per test 2 seconds memory limit per test 64 megabytes input standard input output standard output As you know, Bob's brother lives in Flatland. In Flatland there are n cities, connected by n - 1 two-way roads. The cities are numb…

题目大意:给你一棵树,点有点权$a_{i}$,边有边权$w_{e}$,定义一种路径称为$2-path$,每条边最多经过2次且该路径的权值为$\sum _{x} a_{x}\;-\;\sum_{e}w_{e}\cdot k_{e}$,$k_{e}$为边的经过次数,一共$Q$次询问,每次查询经过$x,y$的$2-path$权值最大的路径的权值 看题解之前感觉不可做...有点思路但感觉不靠谱,都被我否掉了 LiGuanlin神犇提供了一种树形DP的解法 定义$f[x][0]$表示该子树内,经过$x$点…

Find Metal Mineral Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65768/65768 K (Java/Others)Total Submission(s): 3397    Accepted Submission(s): 1588 Problem Description Humans have discovered a kind of new metal mineral on Mars which are d…

Paladin Manao caught the trail of the ancient Book of Evil in a swampy area. This area contains n settlements numbered from 1 to n. Moving through the swamp is very difficult, so people tramped exactly n - 1 paths. Each of these paths connects some p…

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=4003 Humans have discovered a kind of new metal mineral on Mars which are distributed in point‐like with paths connecting each of them which formed a tree. Now Humans launches k robots on Mars to collect…

Walking Race Time Limit: 10000MS   Memory Limit: 131072K Total Submissions: 5409   Accepted: 1371 Case Time Limit: 3000MS Description flymouse’s sister wc is very capable at sports and her favorite event is walking race. Chasing after the championshi…

Walking Race Time Limit: 10000MS   Memory Limit: 131072K Total Submissions: 4123   Accepted: 1029 Case Time Limit: 3000MS Description flymouse’s sister wc is very capable at sports and her favorite event is walking race. Chasing after the championshi…