http://poj.org/problem?id=2186 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 are given up to M (1 <= M <= 50,000) ordered pairs of the form (A, B) that tell you that co…

                                                                                                           Popular Cows Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 39115   Accepted: 15937 Description Every cow's dream is to become th…

题目大意: n头牛,m个崇拜关系,并且崇拜具有传递性 如果a崇拜b,b崇拜c,则a崇拜c 求最后有几头牛被所有牛崇拜 强连通分量内任意两点都能互达 所以只要强联通分量内有一点是 那么其它点也都会是 按照崇拜关系 即a崇拜b就连一条a到b的边 tarjan求得所有强联通分量并染色 而把一个强联通分量缩成一个超级点后 整个图的崇拜关系就变成了一个 有向无环图 此时被所有牛崇拜的牛就是 一个出度为0的超级点 只要把所有边再走一遍就可以计算出度 同时计算每个超级点内有多少个点 即从a出发到b的边 若a…

题意:求其他所有牛都认为其牛的牛的个数. 解题关键:targin算法模板题,缩点形成一棵树,并不一定是棵树,可能含有多个入度为0的点,寻找出度为0的点(缩点之后的点)的个数,如果个数大于0,则无解,否则输出该强连通分量内的个数. 注意targin算法的数组不需要memset. #include<iostream> #include<cstring> #include<cstdio> #include<cstdlib> #include<cmath>…

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 are given up to M (1 <= M <= 50,000) ordered pairs of the form (A, B) that tell you that cow A thinks that cow B is popular. Since pop…

题意:给出一个有向图代表牛和牛喜欢的关系,且喜欢关系具有传递性,求出能被所有牛喜欢的牛的总数(除了它自己以外的牛,或者它很自恋). 思路:这个的难处在于这是一个有环的图,对此我们可以使用tarjan算法求出强连通分量,把强连通分量压缩成一个点,构成一个新的图,这个图一定是没有环的,如果有环就跟强连通分量的矛盾了.压缩成无环图以后这个图里面的点是不具有方向的,我们通过遍历每个节点所能连到的点,如果两点的id值即所在的强连通分量区域不同时,我们就把这个节点的出度加1.最后去找那些出度等于0的点,如果…

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 are given up to M (1 <= M <= 50,000) ordered pairs of the form (A, B) that tell you that cow A thinks that cow B is popula…

这里的Tarjan是基于DFS,用于求有向图的强联通分量. 运用了一个点dfn时间戳和low的关系巧妙地判断出一个强联通分量,从而实现一次DFS即可求出所有的强联通分量. §有向图中, u可达v不一定意味着v可达u.    相互可达则属于同一个强连通分量    (Strongly Connected Component, SCC) §有向图和它的转置的强连通分量相同 §所有SCC构成一个DAG(有向无环图) dfn[u]为节点u搜索的次序编号(时间戳),即首次访问u的时间 low[u]为u或u的…

id=2186">http://poj.org/problem? id=2186 Popular Cows Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 23819   Accepted: 9767 Description Every cow's dream is to become the most popular cow in the herd. In a herd of N (1 <= N <=…

Popular Cows Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 35644   Accepted: 14532 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 are given up to M (1 <= M &…