poj2349 Arctic Network - 最小生成树

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>

using namespace std;
//n个卫星，m个基站
int n, m;
int x, y;
const int maxn = 505;
const int INF = 0x3f3f3f3f;
int parent[maxn];
//有多少个边
int num;  
//ans数组中存储的是升序排序的入树的边的权值
double ans[maxn];

struct point
{
    int x;
    int y;
} p[maxn];

struct ds
{
    int u;
    int v;
    double w;
} d[maxn * maxn + maxn];

double dist(const point& a, const point& b)
{
    return sqrt(1.0 * (a.x - b.x) * (a.x - b.x) +
                1.0 * (a.y - b.y) * (a.y - b.y));
}

bool cmp(const ds &a, const ds& b)
{
    return a.w < b.w;
}

//并查集中找到父节点的操作
int Find(int x)
{
    //递归？
    //parent[x] = Find(parent[x]);
    //return parent[x];

    //自己写的迭代
    int tmp = x;
    while(parent[tmp] != tmp)
    {
        tmp = parent[tmp];
    }

    return tmp;
}

void merge(int x, int y)
{
    int fa = Find(x);
    int fb = Find(y);
    if(fa != fb)
    {
        parent[fa] = fb;
    }
}

void init()
{
    scanf("%d%d",&n,&m);
    num = 0;
    for(int i = 0 ; i < m ; i++)
    {
        scanf("%d%d",&p[i].x,&p[i].y);
    }

    for(int i = 0; i < m ; i++)
        for(int j = i + 1; j < m ; j++)
        {
            d[num].u = i;
            d[num].v = j;
            d[num++].w = dist(p[i],p[j]);
        }

    for(int i = 0 ; i <= m ; i++)  
        parent[i] = i;

    //从小到大进行排序
    sort(d,d+num,cmp);
}

//最主要的代码：Kruskal
void kruskal()
{
    int cnt = 0 ;
    for(int i = 0 ; i < num ; i++)
    {
        int fa = Find(d[i].u);
        int fb = Find(d[i].v);

        if(fa != fb)
        {
            merge(d[i].u,d[i].v);
            ans[cnt++] = d[i].w;
        }
    }
     printf("%.2f\n",ans[cnt - n]);
}

int main()
{
    int t;

    scanf("%d",&t);

    while(t--)
    {
        init();
        kruskal();
    }
    return 0;
}