UVA 10369 Arctic Network

最小生成树问题，kruskal算法的变形。

代码如下：

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#define MAXN1 500+10
#define MAXN 3000000

int z, n, s, m, x[MAXN1], y[MAXN1], u[MAXN], v[MAXN], p[MAXN1], r[MAXN];
double w[MAXN], flag[MAXN];

int cmp(const void *_p, const void *_q)
{
    int *p = (int *)_p;
    int *q = (int *)_q;
    return w[*p] > w[*q] ? 1: -1;
}
int find(int o) {return p[o] == o ? o : p[o] = find(p[o]);}
double kruskal()
{
    int q = 0;
    for(int i = 0; i <= m; i ++) p[i] = i;
    for(int i = 0; i <= z; i ++) r[i] = i;
    qsort(r, z, sizeof(r[0]), cmp);
    for(int i = 0; i < z; i ++)
    {
        int e = r[i]; int x1 = find(u[e]); int y1 = find(v[e]);
        if(x1 != y1) { p[x1] = y1;flag[q++] = w[e];}
    }
    return flag[q-s];
}
void init()
{
    while(~scanf("%d",&n))
        while(n --)
        {
            scanf("%d%d",&s,&m);
            for(int i = 1; i <= m; i ++)
                scanf("%d%d",&x[i],&y[i]);
            z = 0; 
            for(int i = 1; i <= m; i ++)
                for(int j = i+1; j <= m; j ++)
                {
                    u[z] = i; v[z] = j;
                    w[z++] = sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
                }
            printf("%.2lf\n",kruskal());
        }
}
int main()
{
    init();
    return 0;
}