学步园

#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;

const int maxn=55;
struct point
{
    int x,y;
}pnt[maxn];
struct edge
{
    int s,e;
    double len;
    bool operator < (edge e) const
    {
        return len < e.len;
    }
}e[maxn*maxn];
int father[maxn];

double getlen(point a,point b)
{
    return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) );
}

int find(int x)
{
    if(father[x]==x)
    {
        return x;
    }
    return find(father[x]);
}

int main()
{
    int n;
    while(~scanf("%d",&n),n)
    {
        int i,j,p,q;
        scanf("%d%d",&p,&q);
        int ne=0;
        for(i=1;i<=n;i++)
        {
            scanf("%d%d",&pnt[i].x,&pnt[i].y);
            for(j=1;j<i;j++)
            {
                e[ne].s=i;
                e[ne].e=j;
                e[ne++].len=getlen(pnt[i],pnt[j]);
            }
        }

        sort(e,e+ne);
        for(i=1;i<=n;i++)
        {
            father[i]=i;
        }
        double ans=getlen(pnt[p],pnt[q]);
        father[p]=q;

        int u,v;
        for(i=0;i<ne;i++)
        {
            u=find(e[i].s);
            v=find(e[i].e);
            if(u!=v)
            {
                ans += e[i].len;
                father[u] = v;
            }
        }

        printf("%.2lf\n",ans);
    }
    return 0;
}