【模板】【最小树形图】

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
/*
 * 最小树形图
 * int型
 * 复杂度O(NM)
 * 点从0开始
 */
const int INF = 0x3f3f3f3f;
const int MAXN = 1010;
const int MAXM = 40010;
struct Edge
{
	int u,v;
	double cost;
};
struct Point{
	double x, y;
	double GetDist(const Point &p) const{
		return sqrt((x - p.x) * (x - p.x) + (y - p.y) * (y - p.y));
	}
};
Point p[MAXN];
Edge edge[MAXM];
int pre[MAXN],id[MAXN],visit[MAXN];
double in[MAXN];

//root 根节点，n点个数，m边条数，edge边数组
double zhuliu(int root,int n,int m,Edge edge[])
{
	double res = 0;
	int u,v;
	while(1)
	{
		for(int i = 0;i < n;i++)
			in[i] = INF;
		for(int i = 0;i < m;i++)
			if(/*edge[i].u != edge[i].v && */edge[i].cost < in[edge[i].v])
			{
				pre[edge[i].v] = edge[i].u;
				in[edge[i].v] = edge[i].cost;
			}
		for(int i = 0;i < n;i++)
			if(i != root && in[i] == INF)
				return -1.0;//不存在最小树形图
		int tn = 0;
		memset(id,-1,sizeof(id));
		memset(visit,-1,sizeof(visit));
		in[root] = 0;
		for(int i = 0;i < n;i++)
		{
			res += in[i];
			v = i;
			while( /*visit[v] != i*/ visit[v] == -1 /*&& id[v] == -1 */ && v != root)
			{
				visit[v] = i;
				v = pre[v];
			}
			if( v != root && visit[v] == i /*id[v] == -1*/)
			{
				for(int u = pre[v]; u != v ;u = pre[u])
					id[u] = tn;
				id[v] = tn++;
			}
		}
		if(tn == 0)break;//没有有向环
		for(int i = 0;i < n;i++)
			if(id[i] == -1)
				id[i] = tn++;
		for(int i = 0;i < m;)
		{
			v = edge[i].v;
			edge[i].u = id[edge[i].u];
			edge[i].v = id[edge[i].v];
			if(edge[i].u != edge[i].v)
				edge[i++].cost -= in[v];
			else
				swap(edge[i],edge[--m]);
		}
		n = tn;
		root = id[root];
	}
	return res;
}
double g[MAXN][MAXN];
int main()
{
	int n,m;
	while(~scanf("%d%d",&n,&m)){
		for(int i = 0;i < n;i++)
			for(int j = 0;j < n;j++)
				g[i][j] = INF;
		for(int i = 0; i < n; i++){
			scanf("%lf %lf", &p[i].x, &p[i].y);
		}
		int u,v;
		while(m--)
		{
			scanf("%d%d",&u,&v);
			if(u == v)continue;
			u -= 1; v -= 1;
			g[u][v] = min(g[u][v],p[u].GetDist(p[v]));
		}
		int L = 0;
		for(int i = 0;i < n;i++)
			for(int j = 0;j < n;j++)
				if(g[i][j] < INF)
				{
					edge[L].u = i;
					edge[L].v = j;
					edge[L++].cost = g[i][j];
				}
		double ans = zhuliu(0,n,L,edge);
		if(ans == -1.0)printf("poor snoopy\n");
		else printf("%.2f\n",ans);
	}
	return 0;
}