[ An Ac a Day ^_^ ][kuangbin带你飞]专题六 最小生成树 POJ 2031 Building a Space Station

最小生成树模板题

注意最后输出用%f

（从C99开始%f已经不能用于输出double 即 输入用%lf 输出用%f）

 #include<cstdio>
 #include<algorithm>
 #include<cmath>
 #include<cstring>
 #include<string>
 #define M(a,b) memset(a,b,sizeof(a))
 #define debug(x) cerr<<#x<<"=="<<(x)<<endl
 using namespace std;
 typedef long long ll;

 const int maxn=;

 int f[maxn],tol,n;

 struct _edge
 {
     int u,v;
     double w;
 }edge[maxn*maxn*maxn];

 bool cmp(_edge a,_edge b)
 {
     return a.w<b.w;
 }

 struct point
 {
     int a;
     double x,y,z,r;
 } pt[maxn];

 void addedge(point a,point b)
 {
     edge[tol].u=a.a;
     edge[tol].v=b.a;
     double len=sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z))-a.r-b.r;
     edge[tol].w=len<?:len;
     tol++;
 }

 //void addedge(int u,int v,int w)
 //{
 //    edge[tol].u=u;
 //    edge[tol].v=v;
 //    edge[tol].w=w;
 //    tol++;
 //}

 int _find(int x)
 {
     if(f[x]==-) return x;
     else return f[x]=_find(f[x]);
 }

 double kruskal()
 {
     M(f,-);
     sort(edge,edge+tol,cmp);
     int cnt=;
     double ans=,w;
     int u,v,f1,f2;
     for(int i=; i<tol; i++)
     {
         u=edge[i].u;
         v=edge[i].v;
         w=edge[i].w;
         f1=_find(u);
         f2=_find(v);
         if(f1!=f2)
         {
             ans+=w;
             f[f1]=f2;
             cnt++;
         }
         if(cnt==n-) break;
     }
     return ans;
 }

 int main()
 {
     while(scanf("%d",&n)!=EOF&&n)
     {
         tol=;
         double x,y,z,r;
         for(int i=; i<n; i++)
         {
             pt[i].a=i;
             scanf("%lf%lf%lf%lf",&pt[i].x,&pt[i].y,&pt[i].z,&pt[i].r);
             for(int j=; j<i; j++)
             {
                 addedge(pt[j],pt[i]);
             }
         }

         printf("%.3f\n",kruskal()); //注意要用%f
     }
     return ;
 }
 /*

 3
 10.000 10.000 50.000 10.000
 40.000 10.000 50.000 10.000
 40.000 40.000 50.000 10.000
 2
 30.000 30.000 30.000 20.000
 40.000 40.000 40.000 20.000
 5
 5.729 15.143 3.996 25.837
 6.013 14.372 4.818 10.671
 80.115 63.292 84.477 15.120
 64.095 80.924 70.029 14.881
 39.472 85.116 71.369 5.553
 0

 */