poj2349

最小生成树，克鲁斯卡尔

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//poj2349

#include <iostream>

#include <algorithm>

#include <queue>

#include <cmath>

using namespace std;



const    int        maxp = 501, maxdist = 20000;



struct

{

    int        x, y;

}point[maxp];



struct edge

{

    int        v;

    double    w;

    edge(double w, int v):w(w),v(v){}

};



int        s, p, lencount;

bool    vused[maxp];

double    len[maxp * maxp], vdist[maxp];



bool operator<(edge a, edge b)

{

    return a.w > b.w;

}



void init()

{

    int        i;



    scanf("%d%d", &s, &p);

    for (i = 0; i < p; i++)

    {

        scanf("%d%d", &point[i].x, &point[i].y);

        vdist[i] = maxdist;

    }

    memset(vused, 0, sizeof(vused));

    lencount = 0;

}



double distance(int a, int b)

{

    return sqrt(double((point[a].x - point[b].x) * (point[a].x - point[b].x) + (point[a].y - point[b].y) * (point[a].y - point[b].y)));

}



void maketree()

{

    int        i, ncount;

    edge    temp(0, 0);

    double    dis;



    priority_queue<edge> pq;

    vdist[0] = 0;

    vused[0] = true;

    ncount = 1;

    pq.push(edge(0, 0));

    while (ncount <= p)

    {

        do

        {

            temp = pq.top();

            pq.pop();

        }while (vused[temp.v] && !pq.empty());

        len[lencount++] = temp.w;

        vused[temp.v] = true;

        ncount++;

        for (i = 0; i < p; i++)

            if (!vused[i])

            {

                dis = distance(temp.v, i);

                if (dis < vdist[i])

                {

                    vdist[i] = dis;

                    pq.push(edge(dis, i));

                }

            }

    }

    sort(len, len + lencount);

    printf("%.2f\n", len[p - s]);

}



int main()

{

    int        t;



    //freopen("t.txt", "r", stdin);

    scanf("%d", &t);

    while (t--)

    {

        init();

        maketree();

    }

    return 0;

}