D - Outlets HDU4463 最小生成树

 NIKE和苹果店要在一起，所以将他们两个放在第一步联结确保相连。

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<iomanip>
#include<cmath>
#define inf 0x3f3f3f3f
const int maxn = 1e5 + 10;
using namespace std;
int father[maxn];
int find(int x) {
    return father[x] == x ? x : father[x] = find(father[x]);
}
void unite(int x, int y) {
    father[find(x)] = find(y);
}
struct rec {
    int x, y;
    double z;
    bool friend operator<(const rec& a, const rec& b) {
        return a.z < b.z;
    }
}e[maxn];
int main()
{
    int t;
    while (scanf("%d", &t), t) {
        double x[110], y[110], z[110], r[110];
        double dis[110][110];
        for (int i = 1;i <= t;i++) {
            scanf("%lf %lf %lf %lf", &x[i], &y[i], &z[i], &r[i]);
        }
        int add = 1;
        for (int i = 1;i < t;i++) {
            for (int j = i + 1;j <= t;j++) {
                dis[i][j] = 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])) - r[i] - r[j];
                e[add].x = i, e[add].y = j, e[add].z = dis[i][j]; add++;
            }
        }
        add--;
        for (int i = 1;i <= t;i++)father[i] = i;
        sort(e + 1, e + 1 + add);
        double ans = 0;
        for (int i = 1;i <= add;i++) {
            int fx = find(e[i].x), fy = find(e[i].y);
            if (fx == fy)continue;
            unite(fx, fy);
            if (e[i].z > 0) {
                ans += e[i].z;
            }
        }
        printf("%.3f\n", ans);

    }
    return 0;
}