Aizu 2224 Save your cats(最大生成树)

emmm,其实也没什么,很简单的模版题.
提示了一个性质,取出生成树后,剩下的区域将不可能封闭.
不是很晦涩,但是也不是一定知道.
aizu真好啊,日本真好啊,真好啊真好啊.

/*  xzppp  */#include <iostream>#include <vector>#include <cstdio>#include <string.h>#include <algorithm>#include <queue>#include <map>#include <string>#include <cmath>#include <set>#include <iomanip>using namespace std;#define FFF freopen("in.txt","r",stdin);freopen("out.txt","w",stdout);#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1#define MP make_pair#define PB push_backtypedef long long  LL;typedef unsigned long long ULL;typedef pair<int,int > pii;typedef pair<double,double > pdd;typedef pair<double,int > pdi;const int MAXN = 1e4+17;const int MAXM = 20;const int MAXV = 1e4+17;const int INF = 0x7fffffff;const int MOD = 1e9+7;pdd all[MAXV];vector<pdi > G[MAXV];double s;bool vis1[MAXV];void dfs(int x){    vis1[x]=1;    for (int i = 0; i < G[x].size(); ++i)    {        if(!vis1[G[x][i].second])        {            s+=G[x][i].first;        }    }    for (int i = 0; i < G[x].size(); ++i)    {        if(!vis1[G[x][i].second])        {            dfs(G[x][i].second);        }    }}bool vis[MAXV];double minc[MAXV];double prim(int x){    for (int i = 0; i < MAXV; ++i)    {        minc[i] = 0;        vis[i] = 0;    }    double res = 0;    priority_queue<pdi> q;    q.push(MP(0,x));    while(!q.empty())    {        int v = q.top().second;        double temp = q.top().first;        q.pop();        if(vis[v]) continue;        vis[v] = 1;        res += temp;        for (int i = 0; i < G[v].size(); ++i)        {            double d = G[v][i].first;            int to = G[v][i].second;            if(!vis[to]&&minc[to]<d)            {                q.push(MP(d,to));                minc[to] = d;            }        }    }    return  res;}int main(){    #ifndef ONLINE_JUDGE     //FFF    #endif    int n,m;    cin>>n>>m;    for (int i = 0; i < n; ++i)    {        double x,y;        scanf("%lf%lf",&x,&y);        all[i].first = x;        all[i].second = y;    }    for (int i = 0; i < m; ++i)    {        int u,v;        scanf("%d%d",&u,&v);        u--;v--;        double dis = sqrt((all[u].first-all[v].first)*(all[u].first-all[v].first)            +(all[u].second-all[v].second)*(all[u].second-all[v].second));        G[u].push_back(MP(dis,v));        G[v].push_back(MP(dis,u));    }    double ans = 0;    for (int i = 0; i < n; ++i)    {        if(!vis1[i])        {            s = 0;            dfs(i);            double left = prim(i);            ans += s-left;        }    }    cout<<fixed<<setprecision(4)<<ans<<endl;    return 0;}