POJ 2349 Arctic Network

Arctic Network 
#include<stdio.h>
#include<math.h>
#include<algorithm>
using namespace std;
int father[550], m, k;
double d[550];
struct post
{
    double x, y;
}p[550];
struct edge
{
    int u, v;
    double w;
}e[500005];
bool comp(edge e1, edge e2)
{
    return  e1.w < e2.w;
}
double get_dis(double x1, double y1, double x2, double y2)
{
    return sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
}
void Init(int n)
{
    for(int i = 1; i <= n; i++)
        father[i] = i;
}
int Find(int x)
{
    if(x != father[x])
        father[x] = Find(father[x]);
    return father[x];
}
void Merge(int a, int b)
{
    int p = Find(a);
    int q = Find(b);
    if(p > q)
        father[p] = q;
    else
        father[q] = p;
}
void Kruskal(int n)
{
    k = 0;
    double Max = 0;
    for(int i = 0; i < m; i++)
        if(Find(e[i].u) != Find(e[i].v))
        {
            Merge(e[i].u, e[i].v);
            d[k++] = e[i].w;
            n--;
            if(n == 1)
                return;
        }
}
int main()
{
    int t, S, P, i, j;
    double x, y;
    scanf("%d",&t);
    while(t--)
    {
        m = 0;
        scanf("%d%d",&S,&P);
        Init(P);
        for(i = 1; i <= P; i++)
            scanf("%lf%lf",&p[i].x, &p[i].y);
        for(i = 1; i <= P; i++)
            for(j = i + 1; j <= P; j++)
            {
                e[m].u = i;
                e[m].v = j;
                e[m++].w = get_dis(p[i].x, p[i].y, p[j].x, p[j].y);
                e[m].u = j;
                e[m].v = i;
                e[m++].w = get_dis(p[i].x, p[i].y, p[j].x, p[j].y);
            }
        sort(e, e+m, comp);
        Kruskal(P);
        printf("%.2lf\n",d[P-S-1]);
    }
    return 0;
}