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+…

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: 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…

题意:给你一个无向图,有q次操作,每次连接两个点,问你每次操作后有几个桥 思路:我们先用tarjan求出所有的桥,同时我们可以用并查集缩点,fa表示缩点后的编号,还要记录每个节点父节点pre.我们知道,缩点后形成一棵树,所有边都是桥,连接两点必会成环,环上任意边都不是桥.所以连点后,我们把两个点一步一步往上走,如果往上走之后发现fa不一样,说明走过了一条桥,那么合并fa,桥数量-1. 代码: #include<set> #include<map> #include<stack…

题意:一个有向图.第一问:最少给几个点信息能让所有点都收到信息.第二问:最少加几个边能实现在任意点放信息就能传遍所有点 思路:把所有强连通分量缩成一点,然后判断各个点的入度和出度 tarjan算法:问问神奇海螺啥是tarjan 代码: #include<cstdio> #include<cstring> #include<cstdlib> #include<cctype> #include<queue> #include<cmath>…

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…

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…

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=2531 题意 :有N台电脑,每两台电脑之间都有个通信量C[i][j]; 问如何将其分成两个子网,能使得子网之间的通信量最大. 也就是说将所有节点分为两个子集,A,B.求A的各个元素与B的各个元素之间距离的和. 思路:分类在搜索里,一开始也没看懂题,后来连人家的题解都看不懂,这个就像是翻黑白棋问题,一个点要么属于A,要么属于B,只要枚举出所有的状态来就行了 #include <iostream> #include <string.h&g…

Network of Schools Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 13800   Accepted: 5504 Description A number of schools are connected to a computer network. Agreements have been developed among those schools: each school maintains a li…

Network of Schools 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…

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…

以防万一,题目原文和链接均附在文末.那么先是题目分析: [一句话题意] 给定长宽的黑白棋棋盘摆满棋子,每次操作可以反转一个位置和其上下左右共五个位置的棋子的颜色,求要使用最少翻转次数将所有棋子反转为黑色所需翻转的是哪些棋子(这句话好长...). [题目分析] 盯着奇怪的题目看了半天发现和奶牛没什么卵关系..奶牛智商高了产奶高是什么鬼说法... 这题刚开始被放到搜索的分类下了..然而这和搜索有什么关系..没经验所以想了各种和搜索沾边的方法,结果没想出解法,直到看了网上的题解,压根不是搜索啊有木有.…

Power Network 时间限制: 1 Sec  内存限制: 128 MB 题目描述 A power network consists of nodes (power stations, consumers and dispatchers) connected by power transport lines. A node u may be supplied with an amount s(u) >= 0 of power, may produce an amount 0 <= p(u…

[题目链接] http://poj.org/problem?id=1236 [题目大意] 给出一张有向图,问需要从几个起点出发才能遍历全图, 如果要求从任何一个点出发都能遍历全图,那么最少需要增加几条边 [题解] 先求出SCC,那么对于对于第一问,就是入度为0的SCC数量, 第二问是入度为0和出度为0的SCC数量较大的一个. [代码] #include <cstdio> #include <algorithm> #include <vector> #include &l…

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…