>传送门< 题意:求树的直径 思路:就是道模板题,两遍dfs就求出来了 Code #include <cstdio> #include <iostream> #include <algorithm> #include <vector> using namespace std; typedef pair<int, int> P; const int MAX_N = 1000005; vector<P> G[MAX_N]; i…

用两次dfs求出树的直径,这两次dfs可以写在一起,当然为了方便理解,这里是分开写的. 1 //两次dfs求树的重心 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 using namespace std; 6 7 const int N=40005,M=40005*2; 8 int n,m,tot,p,ed; 9 int d[N],head[N],to[M],w[M],nxt[M]; 10…

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…

题目大意:给你一棵树,要你求树的直径的长度 思路:随便找个点bfs出最长的点,那个点一定是一条直径的起点,再从那个点BFS出最长点即可 以下研究了半天才敢交,1.这题的输入格式遵照poj1984,其实就是把后面的字母无视即可 2.这题数据量没给,所以把数组开得很大才敢交TUT #include <stdio.h> #include <iostream> #include <string.h> #include <algorithm> #include <…

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…

http://poj.org/problem?id=1985 题意:给出树,求最远距离. 题意: 树的直径. 树的直径是指树的最长简单路. 求法: 两遍BFS :先任选一个起点BFS找到最长路的终点,再从终点进行BFS,则第二次BFS找到的最长路即为树的直径. 原理: 设起点为u,第一次BFS找到的终点v一定是树的直径的一个端点 .证明: 1) 如果u 是直径上的点,则v显然是直径的终点(因为如果v不是的话,则必定存在另一个点w使得u到w的距离更长,则于BFS找到了v矛盾) 2) 如果u不是直径…

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…

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: 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…

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…