zoj 1718 poj 2031 Building a Space Station

最小生成树，用了Kruskal算法。POJ上C++能过，G++不能过。。。 算出每两个圆心之间的距离，如果距离小于两半径之和，那么这两个圆心之间的距离直接等于0，否则等于距离-R[i]-R[j]。

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<algorithm>
using namespace std;
const int maxn = ;
struct abc{ int start, end; double path; }node[maxn];
bool cmp(const abc&a, const abc&b){ return a.path < b.path; }
double x[maxn], y[maxn], z[maxn], r[maxn];
int father[maxn];
int find(int x)
{
    if (x != father[x]) father[x] = find(father[x]);
    return father[x];
}
int main()
{
    int n, i, j;
    while (~scanf("%d", &n))
    {
        if (n == ) break;
        int tot = ;
        for (i = ; i <= n; i++) scanf("%lf%lf%lf%lf", &x[i], &y[i], &z[i], &r[i]);
        for (i = ; i <= n; i++) father[i] = i;
        for (i = ; i <= n; i++)
        {
            for (j = i + ; j <= n; j++)
            {
                node[tot].start = i;
                node[tot].end = j;
                double tt = sqrt((x[i] - x[j])*(x[i] - x[j]) + (y[i] - y[j])*(y[i] - y[j]) + (z[i] - z[j])*(z[i] - z[j]));
                if (tt <= r[i] + r[j]) node[tot].path = ;
                else node[tot].path = tt - r[i] - r[j];
                tot++;
            }
        }
        double ans = ;
        sort(node, node + tot, cmp);
        for (i = ; i < tot; i++)
        {
            int xx = find(node[i].start);
            int yy = find(node[i].end);
            if (xx != yy)
            {
                father[xx] = yy;
                ans = ans + node[i].path;
            }
        }
        printf("%.3lf\n", ans);
    }
    return ;
}