UVa 10397 Connect the Campus

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

struct A{
int x,y;
double z;
}a[500010];
int r[755];
int find_(int x)
{
while(x!=r[x])
x=r[x];
return x;
}

int cmp(A a,A b)
{
return a.z<b.z;
}
int main()
{
int n,m,i,j,k,c,b,x[755],y[755];
while(scanf("%d",&n)!=EOF)
{
for(i=1;i<=n;i++)
scanf("%d%d",&x[i],&y[i]);
for(i=1;i<=n;i++)
r[i]=i;
k=0;
for(i=1;i<=n;i++)
for(j=1;j<=n;j++){
if(i>j){
double s=sqrt(  (x[i]-x[j])*(x[i]-x[j])+ (y[i]-y[j])*(y[i]-y[j]) );
a[++k].x=i;
a[k].y=j;
a[k].z=s;
}
}
scanf("%d",&m);
while(m--){
scanf("%d%d",&c,&b);
int aa=find_(c);
int bb=find_(b);
if(aa!=bb){
r[aa]=bb;
}
}

sort(a+1,a+1+k,cmp);
double ans=0;
for(i=1;i<=k;i++)
{
int aa=find_(a[i].x);
int bb=find_(a[i].y);
if(aa!=bb){
r[aa]=bb;
ans=ans+a[i].z;
}
}
printf("%.2lf\n",ans);

}
return 0;
}