POJ 2349 Arctic Network (最小生成树第K大（小）边)

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<string>
#include<iostream>
#include<cstring>
#include<cmath>
#include<stack>
#include<queue>
#include<vector>
#include<map>
#include<stdlib.h>
#include<algorithm>
#define LL __int64
using namespace std;
const int MAXN=1000+5;
int kase,n,m;
double ans[MAXN*MAXN/2];
int p[MAXN];
struct node
{
    double x,y;
}po[MAXN];
struct edge
{
    int u,v;
    double val;
    bool operator<(const edge A)const
    {
        return val<A.val;
    }
}a[MAXN*MAXN/2];

double calc(node A,node B)
{
    return sqrt( (A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y) );
}

int findfa(int x)
{
    return p[x]==x?x:p[x]=findfa(p[x]);
}
int main()
{
    //freopen("in.txt","r",stdin);
    scanf("%d",&kase);
    while(kase--)
    {
        scanf("%d %d",&n,&m);
        for(int i=1;i<=m;i++)
            scanf("%lf %lf",&po[i].x,&po[i].y);

        int cnt=1;
        for(int i=1;i<=m;i++)
        {
            for(int j=1;j<=m;j++)
            {
                a[cnt].u=i;
                a[cnt].v=j;
                a[cnt++].val=calc(po[i],po[j]);
            }
        }
        sort(a+1,a+1+cnt);
        for(int i=1;i<=m;i++) p[i]=i;

        int res=0;
        for(int i=1;i<=cnt;i++)
        {
            int u=a[i].u;
            int v=a[i].v;
            int x=findfa(u);
            int y=findfa(v);
            if(x!=y)
            {
                p[x]=y;
                ans[res++]=a[i].val;
                if(res==m-1) break;
            }
        }
        if(n==0) printf("%.2lf\n",ans[res-1]);
        else printf("%.2lf\n",ans[res-n]);
    }
    return 0;
}