POJ 2728 Desert King

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cmath>
 5 #include <algorithm>
 6 #include <climits>
 7 #include <vector>
 8 #include <queue>
 9 #include <cstdlib>
10 #include <string>
11 #include <set>
12 #include <stack>
13 #define LL long long
14 #define pii pair<int,int>
15 #define INF 0x3f3f3f3f
16 using namespace std;
17 const int maxn = 1010;
18 int cost[maxn][maxn],p[maxn];
19 int n,x[maxn],y[maxn],z[maxn];
20 bool vis[maxn];
21 double d[maxn],w[maxn][maxn];
22 double Prim(double tmp) {
23     double sumx = 0,sumy = 0;
24     for(int i = 1; i <= n; i++) {
25         p[i] = 1;
26         d[i] = cost[1][i] - tmp*w[1][i];
27         vis[i] = false;
28     }
29     vis[1] = true;
30     d[1] = 0;
31     for(int i = 2; i <= n; i++) {
32         double MST = INF;
33         int index = -1;
34         for(int j = 2; j <= n; j++)
35             if(!vis[j] && d[j] < MST) MST = d[index = j];
36         vis[index] = true;
37         sumx += cost[p[index]][index];
38         sumy += w[p[index]][index];
39         for(int j = 1; j <= n; j++)
40             if(!vis[j] && d[j] > cost[index][j] - tmp*w[index][j]) {
41                 d[j] = cost[index][j] - tmp*w[index][j];
42                 p[j] = index;
43             }
44     }
45     return sumx/sumy;
46 }
47 int main() {
48     while(scanf("%d",&n),n) {
49         for(int i = 1; i <= n; i++) {
50             scanf("%d %d %d",x+i,y+i,z+i);
51             for(int j = 1; j < i; j++) {
52                 cost[i][j] = cost[j][i] = abs(z[i] - z[j]);
53                 double tmp = (x[i] - x[j])*(x[i] - x[j]) + (y[i] - y[j])*(y[i] - y[j]);
54                 w[i][j] = w[j][i] = sqrt(tmp);
55             }
56         }
57         double ans = 0;
58         while(true) {
59             double tmp = Prim(ans);
60             if(fabs(ans - tmp) < (1e-4)) break;
61             ans = tmp;
62         }
63         printf("%.3f\n",ans);
64     }
65     return 0;
66 }