图论trainning-part-1 H. Qin Shi Huang's National Road System

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cstdlib>
 5 #include <vector>
 6 #include <climits>
 7 #include <algorithm>
 8 #include <cmath>
 9 #define LL long long
10 #define INF 0x3f3f3f
11 using namespace std;
12 const int maxv = 1010;
13 const int maxe = 500*1010;
14 struct arc{
15     int u,v;
16     double w;
17 };
18 int uf[maxv];
19 vector<int>g[maxv];
20 arc e[maxe],tree[maxe];
21 int n,px[maxv],py[maxv],val[maxv];
22 int maxVal,es,ads;
23 double Minst;
24 bool vis[maxv];
25 bool cmp(const arc &x,const arc &y){
26     return x.w < y.w;
27 }
28 void dfs(int u){
29     vis[u] = true;
30     if(val[u] > maxVal) maxVal = val[u];
31     for(int i = 0; i < g[u].size(); i++){
32         if(!vis[g[u][i]]) dfs(g[u][i]);
33     }
34 }
35 int findF(int x){
36     if(x != uf[x])
37         uf[x] = findF(uf[x]);
38     return uf[x];
39 }
40 double dis(int i,int j){
41     double temp = (px[i]-px[j])*(px[i]-px[j])+(py[i]-py[j])*(py[i]-py[j]);
42     return sqrt(temp);
43 }
44 void kruskal(){
45     for(int i = 0; i < es; i++){
46         int x = findF(e[i].u);
47         int y = findF(e[i].v);
48         if(x != y){
49             Minst += e[i].w;
50             uf[x] = y;
51             g[e[i].u].push_back(e[i].v);
52             g[e[i].v].push_back(e[i].u);
53             tree[ads++] = e[i];
54         }
55     }
56 }
57 int main(){
58     int t,i,j;
59     scanf("%d",&t);
60     while(t--){
61         scanf("%d",&n);
62         for(i = 1; i <= n; i++){
63             scanf("%d%d%d",px+i,py+i,val+i);
64             g[i].clear();
65             uf[i] = i;
66         }
67         ads = es = 0;
68         Minst = 0;
69         for(i = 1; i <= n; i++)
70             for(j = i+1; j <= n; j++){
71                 e[es++] = (arc){i,j,dis(i,j)};
72             }
73         sort(e,e+es,cmp);
74         kruskal();
75         double ans = 0,temp;
76         for(i = 0; i < ads; i++){
77             int u = tree[i].u;
78             int v = tree[i].v;
79             memset(vis,false,sizeof(vis));
80             vis[v] = true;
81             temp = maxVal = 0;
82             dfs(u);
83             temp += maxVal;
84             memset(vis,false,sizeof(vis));
85             maxVal = 0;
86             vis[u] = true;
87             dfs(v);
88             temp += maxVal;
89             ans = max(ans,temp/(Minst-tree[i].w));
90         }
91         printf("%.2f\n",ans);
92     }
93     return 0;
94 }