POJ2032 Arctic Network(Prim)

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <climits>
#include <cstring>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <vector>
#include <list>
#include<functional>
#define mod 1000000007
#define inf 0x3f3f3f3f
#define pi acos(-1.0)
using namespace std;
typedef long long ll;
const int N=2005;
const int M=15005;
double edg[N][N];
double lowcost[N];//记录未加入树集合的i离树集合中元素最小的距离
int n,m,t,v;
double d[N];
bool cmp(double a,double b){
return a<b;
}
struct man
{
    double x,y;int num;
}a[N];
double fun(man a,man b)
{
   double cnt=sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
   return cnt;
}
void Build()
{
    for(int i=0;i<n;i++)
    {
        for(int j=i+1;j<n;j++)
        {
            edg[i][j]=edg[j][i]=fun(a[i],a[j]);
        }
    }
}
void prim()
{
    double sum=0;lowcost[0]=-1;
    for(int i=1;i<n;i++){
        lowcost[i]=edg[0][i];
    }
    for(int i=1;i<n;i++){
        double minn=inf;int k;
        for(int j=0;j<n;j++){
            if(lowcost[j]!=-1&&lowcost[j]<minn){
                k=j;minn=lowcost[j];
            }
        }
        sum+=minn;
       d[v++]=minn;
        lowcost[k]=-1;
        for(int j=0;j<n;j++){
            lowcost[j]=min(lowcost[j],edg[k][j]);
        }
    }
    sort(d,d+v,cmp);
    printf("%.2lf\n",d[n-m-1]);
}
int main() {
    scanf("%d",&t);
    while(t--) {
        memset(edg,0,sizeof(edg));
        memset(lowcost,0,sizeof(lowcost));
        memset(d,0,sizeof(d));
        v=0;
        scanf("%d%d",&m,&n);
        for(int i=0;i<n;i++){
            scanf("%lf%lf",&a[i].x,&a[i].y);
            a[i].num=i;
        }
        Build();
        prim();
    }
    return 0;
}