（最小生成树/最小瓶颈生成树） 2017武汉现场赛 - Wifi Relay

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 
 5 
 6 using namespace std;
 7 
 8 const int inf = 0x3f3f3f3f;
 9 const int maxn = 10010;
10 
11 double x[maxn];
12 double y[maxn];
13 
14 int n;
15 
16 double lowc[maxn];
17 bool vis[maxn];
18 
19 double dis(double x1, double y1, double x2, double y2) {
20     return sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2));
21 }
22 
23 double prim() {
24     double res = 0;
25     memset(vis, 0, sizeof(vis));
26     vis[0] = true;
27     for(int i = 1; i < n; i++)lowc[i] = dis(x[0], y[0], x[i], y[i]);
28     for(int i = 1; i < n; i++) {
29         double minc = inf;
30         int p = -1;
31         for(int j = 0; j < n; j++) {
32             if(!vis[j] && lowc[j] < minc) {
33                 minc = lowc[j];
34                 p = j;
35             }
36         }
37         res = max(res, minc);
38         vis[p] = true;
39         for(int j = 0; j < n; j++) {
40             double d = dis(x[p], y[p], x[j], y[j]);
41             if(!vis[j] && lowc[j] > d) {
42                 lowc[j] = d;
43             }
44         }
45     }
46     return res / 2;
47 }
48 
49 
50 int main() {
51     while(~scanf("%d", &n)) {
52         for(int i = 0; i < n; i++) {
53             scanf("%lf%lf", &x[i], &y[i]);
54         }
55         printf("%.9f\n", prim());
56 
57     }
58 
59     return 0;
60 
61 }