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| #include <iostream>
#include <algorithm>
#include <math.h>
using namespace std;
const int maxn = 1e4;
int n,m;
struct edge {
double x,y,z,r;
edge(){}
edge(double a,double b,double c,double d) {
x = a; y = b; z = c; r = d;
}
} edges[maxn];
struct node {
int from,to;
double div;
node () {}
node (int u,int v,double w) {
from = u; to = v; div = w;
}
bool operator<(const node& temp)const {
return this->div < temp.div;
}
}e[maxn];
int pre[maxn];
int find(int x) {
if (x == pre[x]) return x;
else return pre[x] = find(pre[x]);
}
double Distance(edge& a,edge& b) {
double dx = (a.x-b.x)*(a.x-b.x);
double dy = (a.y-b.y)*(a.y-b.y);
double dz = (a.z-b.z)*(a.z-b.z);
return sqrt(dx+dy+dz);
}
int main() {
while (scanf("%d",&n) && n) {
double x,y,z,r;
for (int i=0; i<n; i++) {
cin >> x >> y >> z >> r;
edges[i] = edge(x,y,z,r);
}
int cnt = 0;
for (int i=0; i<n; i++) {
for (int j=0; j<n; j++) {
double dis = Distance(edges[i],edges[j]);
if (dis <= edges[i].r + edges[j].r) {
e[cnt++] = node(i,j,0);
} else {
e[cnt++] = node(i,j,dis - edges[i].r - edges[j].r);
}
}
}
for (int i=0; i<n; i++) pre[i] = i;
sort(e,e+cnt);
double ans = 0;
for (int i=0; i<cnt; i++) {
int a = e[i].from;
int b = e[i].to;
if (find(a) != find(b)) {
ans += e[i].div;
pre[find(a)] = find(b);
}
}
printf("%.3lf\n",ans);
}
return 0;
}
|