POJ2560 通らない

gistfile1.cpp

#include<cstdio>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
vector<pair<double,pair<int,int> > > edges;
vector<int> parent;
int find(int a){
    if(parent[a]==a)return a;
    else return parent[a]=find(parent[a]);
}
void unite(int a,int b){
    int pa=find(a),pb=find(b);
    if(pa!=pb)parent[pa]=pb;
}
int main(){
    int n;
    scanf("%d",&n);
    vector<pair<double,double> > ps(n);
    parent=vector<int>(n);
    for(int i=0;i<n;i++){
        double x,y;
        scanf("%lf%lf",&x,&y);
        ps[i]=make_pair(x,y);
        parent[i]=i;
    }
    edges=vector<pair<double,pair<int,int> > >();
    for(int i=0;i<n;i++){
        for(int j=i+1;j<n;j++){
            edges.push_back(make_pair(pow(ps[i].first-ps[j].first,2)+pow(ps[i].second-ps[j].second,2),make_pair(i,j)));
        }
    }
    sort(edges.begin(),edges.end());
    double ans=0;
    for(int i=0;i<edges.size();i++){
        double le=edges[i].first;
        int a=edges[i].second.first,b=edges[i].second.second;
        if(find(a)!=find(b)){
            unite(a,b);
            ans+=sqrt(le);
        }
    }
    printf("%.2lf\n",ans);
}