http://poj.org/problem?id=2762 Going from u to v or from v to u? Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 12733   Accepted: 3286 Description In order to make their sons brave, Jiajia and Wind take them to a big cave. The cave has…

题目地址:http://poj.org/problem?id=2553 The Bottom of a Graph Time Limit: 3000MS   Memory Limit: 65536K Total Submissions: 7881   Accepted: 3263 Description We will use the following (standard) definitions from graph theory. Let V be a nonempty and finit…

poj.org/problem?id=1236 [题意] 给定一个有向图,求: (1)至少要选几个顶点,才能做到从这些顶点出发,可以到达全部顶点 (2)至少要加多少条边,才能使得从任何一个顶点出发,都能到达全部顶点 [思路] (1)强连通分量缩点后形成一个有向无环图,只要选择入度为0的顶点,其他顶点都可以被到达 (2)等价于一个有向无环图加最少加多少条边能够变成一个强连通图,取出度为0的点的个数和入度为0的点的个数的max,因为出度为0的点要加一条出边,入度为0的点要加一条入边 (2)特判特殊情…

Network of Schools 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 t…

题目链接:http://poj.org/problem?id=2762 题意是 有t组样例,n个点m条有向边,取任意两个点u和v,问u能不能到v 或者v能不能到u,要是可以就输出Yes,否则输出No.注意一点,条件是或者!所以不是判断双连通图的问题. 我一开始没看到'or'这个条件,所以直接tarjan判断是否只有一个强连通分量,果断WA. 所以需要给原图缩点,用tarjan把图变成一个有向无环图,要是只有一个scc,那就直接输出Yes.那接下来讨论多个scc,要是新图中有两个及以上的点的入度为…

Going from u to v or from v to u? Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 15812   Accepted: 4194 Description In order to make their sons brave, Jiajia and Wind take them to a big cave. The cave has n rooms, and one-way corridors…

题目链接:http://poj.org/problem?id=2186 题目意思大概是:给定N(N<=10000)个点和M(M<=50000)条有向边,求有多少个“受欢迎的点”.所谓的“受欢迎的点”当且仅当任何一个点出发都能到达它. 原来的图是无序且可能有环,用tarjan缩点,变成一个DAG.受欢迎点的出度一定为0,所以缩点后求有多少个连通分量的出度是0,要是大于1则没有受欢迎的点,等于1的话求出这个出度为0的连通分量有多少个点. 强联通分量tarjan算法里邻接表用vector一般好理解,…

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=2186 Popular Cows Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 20191   Accepted: 8193 Description Every cow's dream is to become the most popular cow in the herd. In a herd of N (1 <= N <= 10,000) cows, you…

题目链接:https://vjudge.net/contest/295959#problem/I 或者 http://poj.org/problem?id=2762 题意:输入多组样例,输入n个点和m条有向边,问该图中任意两点x, y之间是否满足x可以到y或者y可以到x. 一开始WA的原因是因为没注意到是或者, 如果是并且的话,就是一道简单的强连通分量的题,直接判断整个图是否为一个强连通分量 对于该题, 先用强连通分量进行缩点,简化图.图就变成了DAG,用拓扑排序判断图中点的入度, 图中入度为0…