题目：http://vjudge.net/problem/UVA-11183

题意：以0为根构建一个最小树形图，求最小花费

思路：裸题，没什么好说的

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
using namespace std;

const int N = 1010, INF = 0x3f3f3f3f;
struct edge
{
    int v, u, cost;
}g[N*40];
int n, m, cas;
int in[N], pre[N], id[N], vis[N];
int ma(int s, int n, int m)
{
    int res = 0;
    while(true)
    {
        for(int i = 0; i < n; i++) in[i] = INF;
        for(int i = 0; i < m; i++)
        {
            int v = g[i].v, u = g[i].u;
            if(v != u && g[i].cost < in[u]) in[u] = g[i].cost, pre[u] = v;
        }
        for(int i = 0; i < n; i++)
        {
            if(i == s) continue;
            if(in[i] == INF) return -1;
        }
        int num = 0;
        memset(id, -1, sizeof id);
        memset(vis, -1, sizeof vis);
        in[s] = 0;
        for(int i = 0; i < n; i++)
        {
            res += in[i];
            int v = i;
            while(vis[v] != i && id[v] == -1 && v != s) vis[v] = i, v = pre[v];
            if(v != s && id[v] == -1)
            {
                for(int j = pre[v]; j != v; j = pre[j]) id[j] = num;
                id[v] = num++;
            }
        }
        if(num == 0) break;
        for(int i = 0; i < n; i++)
            if(id[i] == -1) id[i] = num++;
        for(int i = 0; i < m; i++)
        {
            int v = g[i].v, u = g[i].u;
            g[i].v = id[v], g[i].u = id[u];
            if(id[v] != id[u]) g[i].cost -= in[u];
        }
        n = num, s = id[s];
    }
    return res;
}
int main()
{
    int t;
    scanf("%d", &t);
    while(t--)
    {
        scanf("%d%d", &n, &m);
        for(int i = 0; i < m; i++) scanf("%d%d%d", &g[i].v, &g[i].u, &g[i].cost);
        int res = ma(0, n, m);
        if(res != -1) printf("Case #%d: %d\n", ++cas, res);
        else printf("Case #%d: Possums!\n", ++cas);
    }
    return 0;
}