Command Network - POJ 3164 - 最小树形图

题目：

  http://poj.org/problem?id=3164

题意：

  裸最小树形图，套模板就可以。

代码：

#include 
#include 
#include 
#include 
#include 

using namespace std;

#define maxn 107
#define memset(a,b) memset(a,b,sizeof(a))
const int INF = 0x3f3f3f3f;

int pre[maxn],id[maxn],vis[maxn];
double in[maxn];

struct {
    int x,y;
}p[maxn];

struct {
    int u,v;
    double w;
}edge[maxn*maxn];

double dis(int a, int b) {
    double x = p[a].x - p[b].x, y = p[a].y - p[b].y;
    return sqrt(x*x+y*y);
}

double directed_MST(int root, int n, int m) {
    double ans = 0;
    while(true) {
        //1.找最小入边
        for (int i = 0; i < n; i++) in[i] = INF;
        for (int i = 0; i < m; i++) {
            int u = edge[i].u, v = edge[i].v;
            if (edge[i].w < in[v] && u != v) {
                pre[v] = u;
                in[v] = edge[i].w;
            }
        }
        for (int i =0; i < n; i++)
            if (in[i] == INF && i != root)
                return -1;
        //2.找环
        int cnt = 0;
        memset(id, -1);
        memset(vis, -1);
        in[root] = 0;
        for (int i = 0; i < n; i++) {
            ans += in[i];
            int v = i;
            while (vis[v] != i && id[v] == -1) {//缩点
                vis[v] = i;
                v = pre[v];
            }
            if (v != root && id[v] == -1) {
                for (int u = pre[v]; u != v; u = pre[u]) id[u] = cnt;
                id[v] = cnt++;
            }
        }
        if(cnt == 0) break;
        for(int i=0 ; iif(id[i] == -1) id[i] = cnt++;
        //3.建立新图
        for(int i=0 ; iint u = edge[i].u, v = edge[i].v;
            edge[i].u = id[u];
            edge[i].v = id[v];
            if(id[u] != id[v]) edge[i].w -= in[v];
        }
        n = cnt;
        root = id[root];
    }
    return ans;
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("/home/lucienshui/Desktop/in","r",stdin);
#endif
    int n,m;
    while(~scanf("%d%d",&n,&m)) {
        for(int i=0 ; iscanf("%d%d",&p[i].x,&p[i].y);
        for(int i=0 ; iscanf("%d%d",&edge[i].u,&edge[i].v);
            if(--edge[i].u!=--edge[i].v) edge[i].w = dis(edge[i].u,edge[i].v);
            else edge[i].w = INF;
        }
        double ans = directed_MST(0,n,m);
        if(ans == -1) printf("poor snoopy\n");
        else printf("%.2f\n",ans);
    }
    return 0;
}