（最小生成树 Prim） Highways --POJ --1751

#include<cstdio>
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>
using namespace std;
#define N 800
#define INF 0xffffff

struct node {int x, y;}a[N];

int n, m, pre[N];
bool used[N][N], vis[N];
double G[N][N], dist[N];

void prim()
{
    int i, j;
    for(i=1; i<=n; i++)
    {
        dist[i] = G[1][i];
        pre[i] = 1;
    }

    vis[1] = 1;

    for(i=1; i<n; i++)
    {
        int Index = 1;
        double Min = INF;
        for(j=1; j<=n; j++)
        {
            if(!vis[j] && Min>dist[j])
            {
                Min = dist[j];
                Index = j;
            }
        }

        vis[Index] = 1;

        for(j=1; j<=n; j++)
        {
            if(!vis[j] && dist[j] > G[Index][j])
            {
                dist[j] = G[Index][j];
                pre[j] = Index;
            }
        }
    }
}


int main()
{
    while(scanf("%d", &n)!=EOF)
    {
        int i, j, u, v;

        for(i=1; i<=n; i++)
            scanf("%d%d", &a[i].x, &a[i].y);

        for(i=1; i<=n; i++)
        for(j=1; j<=i; j++)
            G[i][j] = G[j][i] = sqrt(1.0*(a[i].x-a[j].x)*(a[i].x-a[j].x) + (a[i].y-a[j].y)*(a[i].y-a[j].y));

        scanf("%d", &m);
        memset(used, 0, sizeof(used));
        for(i=1; i<=m; i++)
        {
            scanf("%d%d", &u, &v);
            G[u][v] = G[v][u] = 0;
            used[u][v] = used[v][u] = 1;
        }
        
        memset(vis, 0, sizeof(vis));
        prim();

        for(i=2; i<=n; i++)
        {
            if(!used[pre[i]][i] && !used[i][pre[i]])
                printf("%d %d\n", i, pre[i]);
        }
    }
    return 0;
}