poj-2728Desert King(最优比率生成树)

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<cmath>
 4 #include<iostream>
 5 #include<algorithm>
 6 #include<queue>
 7 #define N 1007
 8 #define eps 0.000001
 9 using namespace std;
10 
11 int n;
12 double dis[N][N],h[N][N],line[N],p[N][N];
13 bool vis[N];
14 struct Node
15 {
16     double x,y,h;
17 }a[N];
18 
19 double get_dis(int x,int y)
20 {return sqrt((a[x].x-a[y].x)*(a[x].x-a[y].x)+(a[x].y-a[y].y)*(a[x].y-a[y].y));}
21 /*struct cmp
22 {
23     bool operator()(int x,int y)
24     {return line[x]>line[y];}
25 };*/
26 double prim(double num)
27 {
28     for (int i=1;i<=n;i++)
29         for (int j=1;j<=n;j++)
30             p[i][j]=h[i][j]-dis[i][j]*num;
31     //priority_queue<int,vector<int>,cmp>q;
32     //while(!q.empty()) q.pop();
33     memset(vis,0,sizeof(vis));
34     memset(line,127,sizeof(line));
35     line[1]=0;
36     //for (int i=1;i<=n;i++) q.push(i);
37     for (int i=1;i<=n;i++)
38     {
39         int u=0;
40         for (int j=1;j<=n;j++)
41             if (!vis[j]&&line[j]<line[u]) u=j;
42         vis[u]=1;
43         for (int j=1;j<=n;j++)
44             if (!vis[j]) line[j]=min(line[j],p[u][j]);
45     }
46     double sum=0;
47     for (int i=1;i<=n;i++)
48         sum+=line[i];
49     return sum;
50 }
51 int main()
52 {
53     while(~scanf("%d",&n)&&n)
54     {
55         for (int i=1;i<=n;i++)
56             scanf("%lf%lf%lf",&a[i].x,&a[i].y,&a[i].h);
57         for (int i=1;i<=n;i++)
58             for (int j=1;j<=n;j++)
59             {
60                 dis[i][j]=get_dis(i,j);
61                 h[i][j]=fabs(a[i].h-a[j].h);
62             }
63         double l=0.0,r=100.0;
64         while(r-l>=eps)
65         {
66             double mid=(l+r)*1.0/2;
67             if (prim(mid)>=0) l=mid;
68             else r=mid;     
69         }
70         printf("%.3f\n",l);
71     }
72 }