3363: [Usaco2004 Feb]Cow Marathon 奶牛马拉松 Description ​ 最近美国过度肥胖非常普遍,农夫约翰为了让他的奶牛多做运动,举办了奶牛马拉松．马拉 松路线要尽量长,所以,告诉你农场的地图(该地图的描述与上题一致),请帮助约翰寻找两个 最远农场间的距离． Input ​ 第1行:两个分开的整数N和M. ​ 第2到M+1行:每行包括4个分开的内容,Fi,F2,L,D分别描述两个农场的编号,道路的长 度,F1到F2的方向N,E,S,W． Output ​ 一个…

Description 最近美国过度肥胖非常普遍,农夫约翰为了让他的奶牛多做运动,举办了奶牛马拉松．马拉松路线要尽量长,所以,告诉你农场的地图(该地图的描述与上题一致),请帮助约翰寻找两个最远农场间的距离． Input 第1行:两个分开的整数N和M. ​ 第2到M+1行:每行包括4个分开的内容,Fi,F2,L,D分别描述两个农场的编号,道路的长度,F1到F2的方向N,E,S,W． Output 一个整数,表示最远两个衣场间的距离． 明显,这题是求树的直径. 树的直径的定义 树中最远的两个节点之间…

Description 给你一个图,两个点至多有一条路径,求最长的一条路径. \(n \leqslant 4\times 10^4\) Sol DFS?DP? 这就是一棵树,方向什么的都没用... 然后记录一下到这个点的最大值和次大值更新答案即可. Code /************************************************************** Problem: 3363 User: BeiYu Language: C++ Result: Accepted…

http://poj.org/problem?id=1985 题意:就是给你一颗树,求树的直径(即问哪两点之间的距离最长) 分析: 1.树形dp:只要考虑根节点和子节点的关系就可以了 2.两次bfs: ①任意从一个点u出发bfs,设其能到的最远点为v ②从v出发重新bfs,设其能到达的最远点为s ③则树的直径就是v->s 证明: 若能证明从任意一个点出发,bfs到的最远点一定在树的直径的端点上,那么第二次bfs就可以证明一定正确了,下面来证明第一次bfs正确性: ①若选择的点u在直径上,那么能到…

Cow Marathon Time Limit: 2000MS   Memory Limit: 30000K Total Submissions: 3195   Accepted: 1596 Case Time Limit: 1000MS Description After hearing about the epidemic of obesity in the USA, Farmer John wants his cows to get more exercise, so he has com…

Cow Marathon Time Limit: 2000MS   Memory Limit: 30000K Total Submissions: 4185   Accepted: 2118 Case Time Limit: 1000MS Description After hearing about the epidemic of obesity in the USA, Farmer John wants his cows to get more exercise, so he has com…

Cow Marathon Time Limit: 2000MS   Memory Limit: 30000K Total Submissions: 5496   Accepted: 2685 Case Time Limit: 1000MS Description After hearing about the epidemic of obesity in the USA, Farmer John wants his cows to get more exercise, so he has com…

传送门 Cow Marathon Time Limit: 2000MS   Memory Limit: 30000K Total Submissions: 5362   Accepted: 2634 Case Time Limit: 1000MS Description After hearing about the epidemic of obesity in the USA, Farmer John wants his cows to get more exercise, so he has…

题目链接:http://poj.org/problem?id=1985 After hearing about the epidemic of obesity in the USA, Farmer John wants his cows to get more exercise, so he has committed to create a bovine marathon for his cows to run. The marathon route will include a pair o…

Description After hearing about the epidemic of obesity in the USA, Farmer John wants his cows to get more exercise, so he has committed to create a bovine marathon for his cows to run. The marathon route will include a pair of farms and a path compr…