Farthest Nodes in a Tree LightOJ - 1094

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<queue>
 4 #include<algorithm>
 5 using namespace std;
 6 typedef long long LL;
 7 struct Edge
 8 {
 9     LL to,dis,next;
10 }e[60010];
11 LL ne,f1[30010];
12 bool vis[30010];
13 LL ans[30010],anss,T,TT,n;
14 void dfs(LL u)
15 {
16     vis[u]=true;
17     LL k=f1[u],v,ma1=0,ma2=0;
18     priority_queue<LL> q;
19     while(k!=0)
20     {
21         v=e[k].to;
22         if(!vis[e[k].to])
23         {
24             dfs(v);
25             q.push(ans[v]+e[k].dis);
26         }
27         k=e[k].next;
28     }
29     if(!q.empty())
30         ma1=q.top(),q.pop();
31     if(!q.empty())
32         ma2=q.top(),q.pop();
33     anss=max(anss,ma1+ma2);
34     ans[u]=ma1;
35 }
36 int main()
37 {
38     LL i,u,v,w;
39     scanf("%lld",&TT);
40     for(T=1;T<=TT;T++)
41     {
42         memset(vis,0,sizeof(vis));
43         memset(ans,0,sizeof(ans));
44         ne=0;
45         anss=0;
46         memset(f1,0,sizeof(f1));
47         scanf("%lld",&n);
48         for(i=1;i<n;i++)
49         {
50             scanf("%lld%lld%lld",&u,&v,&w);
51             e[++ne].to=v;
52             e[ne].next=f1[u];
53             e[ne].dis=w;
54             f1[u]=ne;
55             e[++ne].to=u;
56             e[ne].next=f1[v];
57             e[ne].dis=w;
58             f1[v]=ne;
59         }
60         dfs(0);
61         printf("Case %lld: %lld\n",T,anss);
62     }
63     return 0;
64 }