最小树形图：简单来说，求一个图的G0的最小树形图，先求出最短弧集合E0。若E0不存在，则图G0的最小树形图不存在。若存在且不含有向环，则E0就是T0中的所有的边。如果E0存在且含有有向环，则收缩有向环为一个点u，并形成图G1，继续且G1的最小树形图直至图Gi，若图Gi无最小树形图，则图G0也不存在最小树形图，若Gi有最小树形图Ti.则逐层展开得到T0

UVA 11183 Teen Girl Squad
Input: Standard Input
Output: Standard Output

– 3 spring rolls please.
– MSG’D!!
– Oh! My stomach lining!
Strong Bad
You are part of a group of n teenage girls armed with cellphones. You have some news you want to tell everyone in the group. The problem is that no two of you are in the same room, and you must communicate using only cellphones. What’s worse is that due to excessive usage, your parents have refused to pay your cellphone bills, so you must distribute the news by calling each other in the cheapest possible way. You will call several of your friends, they will call some of their friends, and so on until everyone in the group hears the news.
Each of you is using a different phone service provider, and you know the price of girl A calling girl B for all possible A and B. Not all of your friends like each other, and some of them will never call people they don’t like. Your job is to find the cheapest possible sequence of calls so that the news spreads from you to all n-1 other members of the group.
Input
The first line of input gives the number of cases, N (N<150). N test cases follow. Each one starts with two lines containing n (0<= n<=1000) and m (0 <= m <= 40,000) . Girls are numbered from 0 to n-1 , and you are girl 0. The next m lines will each contain 3 integers, u, v and w, meaning that a call from girl u to girl v costs w cents (0 <= w <= 1000) . No other calls are possible because of grudges, rivalries and because they are, like, lame. The input file size is around 1200 KB.

Output
For each test case, output one line containing “Case #x:” followed by the cost of the cheapest method of distributing the news. If there is no solution, print “Possums!” instead.

Sample Input Output for Sample Input
4
2
1
0 1 10
2
1
1 0 10
4
4
0 1 10
0 2 10
1 3 20
2 3 30
4
4
0 1 10
1 2 20
2 0 30
2 3 100
Case #1: 10
Case #2: Possums!
Case #3: 40
Case #4: 130

#include
   
     #include
    
      #include
     
       #include
      
        #include
       
         using namespace std; const int maxn=1010; const int INF = 0x3f3f3f3f; const int maxm =40010; struct Edge { int u,v,cost; }edge[maxm]; int pre[maxn],id[maxn],vis[maxn],in[maxn]; int zhuliu(int root,int n,int m,Edge edge[]) { int u,v; int res=0; while(1) { for(int i=0;i