POJ 3164 最小树形图裸题

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题意：

给定n个点 m条有向边（点标从1开始）

下面n个点坐标

下面m条边

问最小树形图权值（无则输出一句话）

思路：最小树形图裸题

#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>#include <math.h>using namespace std;/** 最小树形图* 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;}edge[MAXM];int pre[MAXN],id[MAXN],visit[MAXN];double in[MAXN];double zhuliu(int root,int n,int m,Edge edge[]){int u,v;double res=0;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;//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 && id[v] == -1 && v != root){visit[v] = i;v = pre[v];}if( v != root && 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];elseswap(edge[i],edge[--m]);}n = tn;root = id[root];}return res;}double dis[105][105];struct node{double x,y;}p[105];double Dis(node a, node b){return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}int n, m;int main(){int i, j, u, v; double d;while(~scanf("%d %d", &n, &m)){for(i = 0; i < n; i++){scanf("%lf%lf",&p[i].x,&p[i].y);for(j = 0; j < n; j++)dis[i][j] = INF;}while(m--){scanf("%d%d",&u,&v); u--, v--;dis[u][v] = min(dis[u][v], Dis(p[u],p[v]));}int edgenum = 0;for(i = 0; i < n; i++)if(i!=j)for(j = 0; j < n; j++)if(dis[i][j]<INF){Edge E={i,j,dis[i][j]};edge[edgenum++] = E;}d = zhuliu(0,n,edgenum,edge);if(d<0)puts("poor snoopy");else printf("%.2lf\n", d);}return 0;}

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