poj 3417 Network(tarjan lca) 先给出一棵无根树,然后下面再给出m条边,把这m条边连上,然后每次你能毁掉两条边,规定一条是树边,一条是新边,问有多少种方案能使树断裂. 我们设添加了一条新边后,树形成了一个环,表示为x->y->lca(x,y),我们将其中的边都覆盖一次.添加了多条新边后,可知树上有些边是会被多次覆盖的,画图很容易发现,但一个树边被覆盖了2次或以上,它就是一条牢固的边,就是说毁掉它再毁掉任何一条新边都好,树都不会断裂.所以我们只要统计被覆盖过零次或一次的…

POJ3417:http://poj.org/problem?id=3417 思路 我们注意到由“主要边”构成一颗树 “附加边”则是非树边 把一条附加边(x,y)加入树中 会与树上x,y之间构成一个环 因此 我们称每条附加边(x,y)都把树上x,y之间的路径覆盖一次 我们只需要统计出每条“主要边”被覆盖几次 有以下几种情况 第一步把覆盖0次的主要边切断 则第二步可以任意切一条附加边 ans+=m 第一步把覆盖1次的主要边切断 则第二步只有一种选择切附加边 ans+=1 第一步把覆盖2次或以上的主…

每条额外的边加入到图中,会导致树上一条路径成环,假设没有其余边,那么要将新图分成两部分,如果想删一条成环路径上的边,那么必须把这条额外边也删除. 因此每条额外边加入时,只需将环上的边+1.最后看看每条边被加了几次,被加了x次,也就是说删除这条边,至少还要删除x条边才能被分成两半,如果一次都没有被加,意味着这条边删了就分成两半了,对答案的贡献为m:如果被加了一次,那么对答案的贡献为1:如果被加的次数超过1,那么对答案没有贡献. #include<cstdio> #include<cstri…

题意: 先给出一棵树,然后再给出m条边,把这m条边连上,然后剪掉两条边,一条是原边,一条是新边,问有多少种方案能使图不连通. 思路: 从原边的角度看 1.树加边,一定成环,加一条(u,v)边就有u->lca->v上的边被覆盖一次 2.当一条边没被覆盖时,删去该边与任意一条新边都能使图不连通,即有m种方案 3.当一条边被覆盖1次时,删去与该边成环的新边,即有1种方案 4.当一条边被覆盖1次以上时,没有方案 用树形dp,dp[i]表示第i号点与其父亲相连的边被覆盖的次数.一条新边(u,v)加入则+…

题意: N个点,构成一棵树.给出这棵树的结构. M条边,(a1,b1)...(am,bm),代表给树的这些点对连上边.这样就形成了有很多环的一个新"树". 现在要求你在原树中断一条边,在M条边中断一条边,使得新"树"被分成两个部分. 问有多少种方案. 思路: 连上某条新边(a,b),则必定形成一个环.环的路径是a->...->lca(a,b)->...->b,给这些边的值都加1 . 分情况: 在原树中,若一条边的值>=2,去掉这条边,再…

POJ 1236 Network of Schools(强连通 Tarjan+缩点) ACM 题目地址:POJ 1236 题意:  给定一张有向图,问最少选择几个点能遍历全图,以及最少加入�几条边使得有向图成为一个强连通图. 分析:  跟HDU 2767 Proving Equivalences(题解)一样的题目,只是多了个问题,事实上转化成DAG后就不难考虑了,事实上仅仅要选择入度为0的点即可了. 代码: /* * Author: illuz <iilluzen[at]gmail.com>…

题目连接:problemId=542" target="_blank">ZOJ 1542 POJ 1861 Network 网络 Network Time Limit: 2 Seconds      Memory Limit: 65536 KB      Special Judge Andrew is working as system administrator and is planning to establish a new network in his com…

POJ 1236 Network of Schools 题目链接 题意:题意本质上就是,给定一个有向图,问两个问题 1.从哪几个顶点出发,能走全全部点 2.最少连几条边,使得图强连通 思路: #include <cstdio> #include <cstring> #include <vector> #include <stack> using namespace std; const int N = 105; int n; vector<int>…

题目链接: Poj 3694 Network 题目描述: 给出一个无向连通图,加入一系列边指定的后,问还剩下多少个桥? 解题思路: 先求出图的双连通分支,然后缩点重新建图,加入一个指定的边后,求出这条边两个端点根节点的LCA,统计其中的桥,然后把这个环中的节点加到一个集合中,根节点标记为LCA. 题目不难,坑在了数组初始化和大小 #include <cstdio> #include <cstring> #include <iostream> #include <a…

题目链接: Poj 1236 Network of Schools 题目描述: 有n个学校,学校之间有一些单向的用来发射无线电的线路,当一个学校得到网络可以通过线路向其他学校传输网络,1:至少分配几个网络才能够让所有学校被网络覆盖?2:至少要加几条线路就能做到在任意一个学校安装网络都可以覆盖全部学校? 解题思路: 先用Tarjan对强连通分量进行缩点,然后对缩点以后的图进行处理,统计图中节点出度为零的有多少,入度为零的有多少个? 因为入度为零的点不能由其他的点到达,在每个入度为零的节点安装网络可…

Yixght is a manager of the company called SzqNetwork(SN). Now she's very worried because she has just received a bad news which denotes that DxtNetwork(DN), the SN's business rival, intents to attack the network of SN. More unfortunately, the origina…

http://poj.org/problem?id=3417 Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 5294   Accepted: 1517 Description Yixght is a manager of the company called SzqNetwork(SN). Now she's very worried because she has just received a bad news wh…

Network of Schools Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 16806   Accepted: 6643 Description A number of schools are connected to a computer network. Agreements have been developed among those schools: each school maintains a li…

Network Time Limit: 5000MS   Memory Limit: 65536K Total Submissions: 9434   Accepted: 3511 Description A network administrator manages a large network. The network consists of N computers and M links between pairs of computers. Any pair of computers…

Network Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 8797   Accepted: 4116 Description A Telephone Line Company (TLC) is establishing a new telephone cable network. They are connecting several places numbered by integers from 1 to N .…

Network Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 12707   Accepted: 5835 Description A Telephone Line Company (TLC) is establishing a new telephone cable network. They are connecting several places numbered by integers from 1 to N…

http://poj.org/problem?id=1236 Network of Schools Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 13046   Accepted: 5215 Description A number of schools are connected to a computer network. Agreements have been developed among those scho…

http://poj.org/problem?id=1236 Network of Schools Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 9481   Accepted: 3767 Description A number of schools are connected to a computer network. Agreements have been developed among those schoo…

主题链接: http://poj.org/problem?id=1236 Network of Schools Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 11433   Accepted: 4551 Description A number of schools are connected to a computer network. Agreements have been developed among thos…

Network Time Limit:5000MS     Memory Limit:65536KB     64bit IO Format:%I64d & %I64u Submit Status Practice POJ 3694 Description A network administrator manages a large network. The network consists of N computers and M links between pairs of compute…

Network of Schools Time Limit:1000MS     Memory Limit:10000KB     64bit IO Format:%I64d & %I64u Submit Status Practice POJ 1236 Description A number of schools are connected to a computer network. Agreements have been developed among those schools: e…

http://poj.org/problem?id=2236 An earthquake takes place in Southeast Asia. The ACM (Asia Cooperated Medical team) have set up a wireless network with the lap computers, but an unexpected aftershock attacked, all computers in the network were all bro…

Network Time Limit: 1000MS   Memory Limit: 30000K Total Submissions: 14021   Accepted: 5484   Special Judge Description Andrew is working as system administrator and is planning to establish a new network in his company. There will be N hubs in the c…

Network Time Limit: 1000MS   Memory Limit: 30000K Total Submissions: 14103   Accepted: 5528   Special Judge Description Andrew is working as system administrator and is planning to establish a new network in his company. There will be N hubs in the c…

题目链接:http://poj.org/problem?id=1236 题目大意:有一些学校,学校之间可以进行收发邮件,给出学校的相互关系,问:1.至少 要向这些学校发送多少份才能使所有的学校都能获得邮件:2.若想只发送一份即可让所有学 校都能收到邮件,则至少需要需要再进行多少次学校之间的连接. 学校之间的关系可构成图,将图进行强连通缩点成块儿后可知,每个进入数为0的点需要发 送一份:若想要所有点都连接,则需要连接数目为max(入度为0点数,出度为0点数),这 个是结论,详细证明不再贴. 代码如…

传送门 Description A number of schools are connected to a computer network. Agreements have been developed among those schools: each school maintains a list of schools to which it distributes software (the “receiving schools”). Note that if B is in the…

Network of Schools Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 16803   Accepted: 6641 Description A number of schools are connected to a computer network. Agreements have been developed among those schools: each school maintains a li…

题目链接:http://poj.org/problem?id=3694 题意:n个点,m条边,给你一个连通图,然后有Q次操作,每次加入一条边(A,B),加入边后,问当前还有多少桥,输出桥的个数. 解题思路:先将原连通图边双连通缩点成一颗树,Q次操作过程中对树进行LCA操作.具体看代码: 看网上也有不缩点的方法. 思路参考于:http://www.cnblogs.com/kuangbin/p/3184884.html #include "stdio.h" //poj 3177 边双连通问…

Network of Schools Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 12240   Accepted: 4871 Description A number of schools are connected to a computer network. Agreements have been developed among those schools: each school maintains a li…

题目链接:poj 1144 题意就是说有 n(标号为 1 ~ n)个网点连接成的一个网络,critical places 表示删去后使得图不连通的顶点,也就是割顶,求图中割顶的个数. 直接上大白书上的模板即可,只是输入也有点卡人,我竟然傻傻的用手写的输入挂来处理,看了别人的博客才知道用 scanf("%s") 即可,因为 scanf("%s") 不会读入空格,再适当处理下即可. 我的代码是: #include<cstdio> #include<cs…