POJ 2631 Roads in the North(树的直径) http://poj.org/problem? id=2631 题意: 有一个树结构, 给你树的全部边(u,v,cost), 表示u和v两点间有一条距离为cost的边. 然后问你该树上最远的两个点的距离是多少?(即树的直径) 分析: 对于树的直径问题, <<算法导论>>(22 2-7)例题有说明. 详细解法: 首先从树上随意一个点a出发, (BFS)找出到这个点距离最远的点b. 然后在从b点出发(BFS)找到距离b…

题目连接 http://poj.org/problem?id=2631 Roads in the North Description Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such that there is only one route from a village to…

Roads in the North Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 2359   Accepted: 1157 Description Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such…

Roads in the North Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 4513   Accepted: 2157 Description Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such…

题目链接:http://poj.org/problem?id=2631 Description Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such that there is only one route from a village to a village that does…

Description Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such that there is only one route from a village to a village that does not pass through some other village…

Description Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such that there is only one route from a village to a village that does not pass through some other village…

<题目链接> 题目大意:求一颗带权树上任意两点的最远路径长度. 解题分析: 裸的树的直径,可由树形DP和DFS.BFS求解,下面介绍的是BFS解法. 在树上跑两遍BFS即可,第一遍BFS以任意点为起点,此时得到的离它距离最远的点为树的直径上的端点之一,然后再以这个端点为起点,跑一遍BFS,此时离它最远的点为树直径的另一个端点,同时,它们之间的距离即为树的直径. #include<iostream> #include<cstdio> #include<algorit…

题意: 给定一棵树, 求树的直径. 分析: 两种方法: 1.两次bfs, 第一次求出最远的点, 第二次求该点的最远距离就是直径. 2.同hdu2196的第一次dfs, 求出每个节点到子树的最长距离和次长距离, 然后某个点的最长+次长就是直径. #include<stdio.h> #include<vector> #include<algorithm> #include<string.h> #include<iostream> using name…

树的直径 树的直径求法: 任取一点u,找到树上距u最远的点s 找到树上距s点最远的点t,s->t的距离即为所求 #include <iostream> #include <cstdio> #include <algorithm> #include <cstring> #include <cstdlib> #include <cmath> #include <queue> using namespace std; in…

Roads in the North POJ - 2631 Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such that there is only one route from a village to a village that does not pass through…

POJ 1724 ROADS Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 12766   Accepted: 4722 Description N cities named with numbers 1 ... N are connected with one-way roads. Each road has two parameters associated with it : the road length and…

Description Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such that there is only one route from a village to a village that does not pass through some other village…

题目链接:http://poj.org/problem?id=2631 求树的直径模板. 定理: 树上任意一个点的在树上的最长路一定以树的直径的两端点其中一点结束. 做法: 两边bfs,第一次先找到node(树的直径的两端点其中一个),再一次求node的最长路所结束的点t node->t就是树的直径 #include <queue> #include <cstdio> #include <cstring> #include <iostream> #in…

http://poj.org/problem?id=2631 树的直径裸题 dfs/bfs均可 /* dfs */ #include <iostream> #include <cstdio> #include <algorithm> #include <cmath> #include <cstring> #include <string> using namespace std; ; #define yxy getchar() , p…

http://poj.org/problem?id=2631 2333水题, 有一个小技巧是说随便找一个点作为起点, 找到这个点的最远点, 以这个最远点为起点, 再次找到的最远点就是这个图的最远点 证明可以用三角形定理 #include<iostream> #include<cstdio> #include<vector> #include<cstring> #define maxn 10005 using namespace std; struct don…

Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such that there is only one route from a village to a village that does not pass through some other village twice. Give…

Building and maintaining roads among communities in the far North is an expensive business. With this in mind, the roads are build such that there is only one route from a village to a village that does not pass through some other village twice. Give…

ROADS Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 10777   Accepted: 3961 Description N cities named with numbers 1 ... N are connected with one-way roads. Each road has two parameters associated with it : the road length and the toll…

题目链接: https://cn.vjudge.net/problem/POJ-1724 N cities named with numbers 1 ... N are connected with one-way roads. Each road has two parameters associated with it : the road length and the toll that needs to be paid for the road (expressed in the num…

题意:给你N个城市和M条路和K块钱,每条路有话费,问你从1走到N的在K块钱内所能走的最短距离是多少 链接:http://poj.org/problem?id=1724 直接dfs搜一遍就是 代码: #include <stdio.h> #include <string.h> #include <iostream> #include <algorithm> #include <stdlib.h> #include <vector> #i…

题目链接:http://poj.org/problem?id=1240 本文链接:http://www.cnblogs.com/Ash-ly/p/5482520.html 题意: 通过一棵二叉树的中序和后序遍历序列,就可以得到这颗二叉树的前序遍历序列.类似的,也能通过前序和中序遍历序列来得到后序遍历序列.但是,通常来说,不能通过前序和后序遍历序列来确定一棵二叉树的中序遍历序列.如下面这四颗二叉树: 所有的这四颗二叉树都有着相同的前序(abc)和后序遍历(cba)序列.这个现象不仅仅在二叉树中存在…

题目链接:http://poj.org/problem?id=1724 题目意思:给出一个含有N个点(编号从1~N).R条边的有向图.Bob 有 K 那么多的金钱,需要找一条从顶点1到顶点N的路径(每条边需要一定的花费),前提是这个总花费  <= K. 首先这里很感谢 yunyouxi0 ,也就是我们的ACM队长啦~~~,他一下子指出了我的错误——存储重边的错误.这条题卑鄙的地方是,有重边,discuss 中的数据过了也不一定会AC啦.大家不妨试试这组数据(队长深情奉献^_^) 2 2 2 1…

Constructing Roads Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 20889   Accepted: 8817 Description There are N villages, which are numbered from 1 to N, and you should build some roads such that every two villages can connect to each…

一道写法多样的题,很具有启发性. 具体参考:http://www.cnblogs.com/scau20110726/archive/2013/04/28/3050178.html http://blog.csdn.net/lyy289065406/article/details/6692382…

题目链接 题意:给出一个树形结构,求P个节点的子树最少要去掉几条边 分析:DP[root][j] 表示 以第 root 个为根节点, 包含j 个节点需要去掉几条边.那么对于 root 这个根节点来说, 要么选择 他的一个 儿子 k, 要么不选择, 如果选择 dp[root][j] = min( dp[k][i] + dp[root][j - i] ), k为root的子节点, 其中  0 < i < j: 如果不选择的话,就去掉root 和 k之间连线,dp[root][j] = dp[roo…

题目传送门 题意:问从1到n的最短路径,同时满足花费总值小于等于k 分析:深搜+剪枝,如果之前走过该点或者此时的路劲长度大于最小值就不进行搜索. /************************************************ * Author :Running_Time * Created Time :2015/11/11 星期三 10:14:14 * File Name :POJ_1724.cpp **************************************…

题目链接 用STL实现超时了,用普通队列500+,看到spfa,反应太迟钝了. #include <cstring> #include <cstdio> #include <string> #include <iostream> #include <algorithm> #include <vector> #include <queue> using namespace std; #define INF 0x7ffffff…

题意:有R条路,每条路都有一定的路长和花费,问在总的花费小于一定的值的情况下,从1到N的最短路程         注意:这里两点之间单向边,且可能存在很多条路,所以只能用邻接表存储.思路:用dijkstra,但是每次判断一个元素是否能进入队列,并不是源点到它的距离被更新了才入队, 而是只要满足从源点到该点总的路费小于给定的值,都可入队. 每次从优先级队列中取出路程最小(如果路程相同,取花费最小)的点. 当N点被取出来时,直接结束 #include <iostream> #include <…

题目链接 题意 : 求从1城市到n城市的最短路.但是每条路有两个属性,一个是路长,一个是花费.要求在花费为K内,找到最短路. 思路 :这个题好像有很多种做法,我用了BFS+优先队列.崔老师真是千年不变的SPFA啊,链接.还有一个神用了好几种方法分析,链接 . 用优先队列控制长度,保证每次加的都是最短的,每次从队列中取元素,沿着取出来的点往下找,如果费用比K少再加入队列,否则不加,这样可以省时间. #include <stdio.h> #include <string.h> #inc…