POJ 2031 BUilding a Space Station 两点间距离 + 最小生成树

#include <cmath>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>

using namespace std;

struct P
{
double x,y,z,r;
}p[110];

struct E
{
int u,v;
double w;
}edge[10010];

double cal(P p1,P p2)
{
double w;
w = sqrt( (p1.x-p2.x)*(p1.x-p2.x) + (p1.y-p2.y)*(p1.y-p2.y) + (p1.z-p2.z)*(p1.z-p2.z) );
w -= (p1.r+p2.r);
return w > 0 ? w : 0;
}

int fp[110];

bool cmp(E e1,E e2)
{
return e1.w < e2.w;
}

int find(int x)
{
int k,j,r;
r = x;
while(r != fp[r])
{
r = fp[r];
}

k = x;

while(k != r)
{
j = fp[k];
fp[k] = r;
k = j;
}
return r;
}

bool merge(E e)
{
int fu = find(e.u);
int fv = find(e.v);

if(fu == fv)
return false;
fp[fu] = fv;
return true;
}

int main()
{
int n;

int i,j,top;

double sumw;

while(scanf("%d",&n) && n)
{
for(i = 1;i <= n; ++i)
{
scanf("%lf %lf %lf %lf",&p[i].x,&p[i].y,&p[i].z,&p[i].r);
}
for(i = 1,top = 0;i <= n; ++i)
{
for(j = i+1;j <= n; ++j)
{
edge[top].u = i;
edge[top].v = j;
edge[top++].w = cal(p[i],p[j]);
}
}

sort(edge,edge+top,cmp);

for(i = 1;i <= n; ++i)
fp[i] = i;

for(i = 0,sumw = 0;i < top ; ++i)
{
if(merge(edge[i]))
{
sumw += edge[i].w;
}
}

printf("%.3f\n",sumw);

}
return 0;
}