POJ2349 Arctic Network

题目链接：http://poj.org/problem?id=2349

求最小生成树中第S大的边，结点给的是坐标（坑爹啊）

#include <iostream>#include <cstdio>#include <cstring>#include <cstdlib>#include <cmath>#include <algorithm>using namespace std;#define N 500struct edge{    int u, v;    double w;}e[250000];struct data{    int x, y;}a[N];int S, P, tot, cnt, p[N];double dis(data a, data b){    int x = a.x - b.x;    int y = a.y - b.y;    double xx = x * x;    double yy = y * y;    return sqrt(xx + yy);}int find(int x){    return p[x] != x ? p[x] = find(p[x]) : x;}void add(int x, int y, double z){    tot++;    e[tot].u = x;    e[tot].v = y;    e[tot].w = z;}double cmp(double a, double b){    return a > b;}double cmp2(edge a, edge b){    return a.w < b.w;}int main(){    int r1, r2, t;    double ans, w[250000];    cin >> t;    while (t--)    {        cin >> S >> P;        for (int i = 0; i < P; i++) p[i] = i;        tot = ans = cnt = 0;        memset(e, 0, sizeof(e));        memset(w, 0, sizeof(w));        for (int i = 0; i < P; i++) scanf("%d%d", &a[i].x, &a[i].y);        for (int i = 0; i < P; i++)          for (int j = 0; j < P; j++)          {              if (i != j) add(i, j, dis(a[i], a[j]));          }        sort(e + 1, e + 1 + tot, cmp2);        for (int i = 0; i < tot; i++)        {            r1 = find(e[i].u); r2 = find(e[i].v);            if (r1 != r2)            {                p[r2] = r1; w[cnt++] = e[i].w;            }        }        sort(w, w + cnt, cmp);        if (S == 0) ans = w[0];        else ans = w[S - 1];        printf("%.2lf\n", ans);    }    return 0;}