最小有向生成树

#include <iostream>
#include <cstdio>
#include <sstream>
#include <cstring>
#include <map>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#define rap(i, a, n) for(int i=a; i<=n; i++)
#define MOD 2018
#define LL long long
#define ULL unsigned long long
#define Pair pair<int, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define _  ios_base::sync_with_stdio(0),cin.tie(0)
//freopen("1.txt", "r", stdin);
using namespace std;
const int maxn = 10010, INF = 0x7fffffff;
int n, m;
int vis[maxn], inc[maxn], pre[maxn];
double w[105][105];

struct edge
{
    int x, y;
}Edge[maxn];

void dfs(int u)
{
    vis[u] = 1;
    for(int i=1; i<=n; i++)
        if(!vis[i] && w[u][i] < INF)
            dfs(i);
}


double dirmst(int u)
{
    double ans = 0;
     //==  步骤1： 判断能否形成最小树形图，直接dfs遍历 (就是检验一下图是否能够联通)
    dfs(u);
    for(int i=1; i<=n; i++)
        if(!vis[i])
            return -1;
    //== 如果可以形成最小树形图，继续
    mem(vis, 0);
    while(true)
    {
        //== 1. 找最小前驱边
        for(int i=1; i<=n; i++) if(i != u && !inc[i]){
            w[i][i] = INF; pre[i] = i;
            for(int j=1; j<=n; j++) if(!inc[j] && w[j][i] < w[pre[i]][i])
                pre[i] = j;
        }
        //== 2.判断是否有环
        int i;
        for(i=1; i<=n; i++) if(i != u && !inc[i]){
            int j = i, cnt = 0;
            while(j != u && pre[j] != i && cnt <= n) j = pre[j], ++cnt;
            if(j == u || cnt > n) continue;
            break;
        }
        //== 没有找到环,得到答案
        if(i > n)
        {
            for(int i=1; i<=n; i++) if(i != u && !inc[i]) ans += w[pre[i]][i];
            return ans;
        }
        //==  有环，则对这个环进行收缩
        int j = i;
        mem(vis, 0);
        do{
            ans += w[pre[j]][j], j = pre[j], vis[j] = inc[j] = true;
        }while(j != i);
        inc[i] = false; // 环缩成了点i，点i仍然存在

        for(int k=1; k<=n; k++) if(vis[k]){ //在环中的点
            for(int j=1; j<=n; j++) if(!vis[j]){ //不在环中的点
                if(w[i][j] > w[k][j]) w[i][j] = w[k][j]; //更新环的出边
                if(w[j][k] < INF && w[j][k] - w[pre[k]][k] < w[j][i]) //更新环的入边
                    w[j][i] = w[j][k] - w[pre[k]][k];
            }
        }
    }
    return ans;
}

void init()
{
    mem(vis, 0);
    mem(inc, 0);
    rap(i, 0, n)
        rap(j, i, n)
            w[i][j]  = w[j][i] = INF;
}

int main()
{
    while(~scanf("%d%d", &n, &m))
    {
        init();
        rap(i, 1, n)
        {
            scanf("%d%d", &Edge[i].x, &Edge[i].y);
        }
        rap(i, 1, m)
        {
            int a, b;
            scanf("%d%d", &a, &b);
            double c = sqrt((double)(Edge[a].x - Edge[b].x)*(Edge[a].x - Edge[b].x) + (double)(Edge[a].y - Edge[b].y)*(Edge[a].y - Edge[b].y));
            if(w[a][b] > c)
                w[a][b] = c;
        }
        double ans = dirmst(1);
        if(ans < 0) puts("poor snoopy");
        else printf("%.2f\n", ans);

    }

    return 0;
}