2370 小机房的树

 1 #include<iostream>
 2 #include<vector>
 3 using namespace std;
 4 typedef unsigned long long ll;
 5 const int maxn=50005,maxm=75005;
 6 
 7 
 8 vector<int> G[maxn],dist[maxn],u[maxn],f[maxn];
 9 bool vis[maxn],vt[maxn];
10 int fa[maxn],w[maxm],n;
11 ll anc[maxn];
12 
13 int find(int x)
14 {
15     if(!fa[x])return x;
16     return fa[x]=find(fa[x]);
17 }
18 
19 void uni(int x,int y)
20 {
21     int b=find(y);
22     if(b!=x)fa[b]=x;
23 }
24 
25 void Tarjan(int x,ll k)
26 {
27     anc[x]=k;
28     for(int i=0;i<G[x].size();i++)
29     if(!vt[G[x][i]])
30     {
31         int v=G[x][i];
32         vt[v]=true;
33         Tarjan(v,k+dist[x][i]);
34         uni(x,v);
35     }
36     vis[x]=true;
37     for(int i=0;i<u[x].size();i++)
38     if(vis[u[x][i]])
39     {
40         w[f[x][i]]=anc[x]+anc[u[x][i]]-2*anc[find(u[x][i])];
41     }
42 }
43 int main()
44 {
45     int a,b,c,m;
46     cin>>n;
47     for(int i=1;i<=n-1;i++)
48     {
49         cin>>a>>b>>c;
50         a++,b++;
51         G[a].push_back(b),dist[a].push_back(c);
52         G[b].push_back(a),dist[b].push_back(c);
53     }
54     cin>>m;
55     for(int i=1;i<=m;i++)
56     {
57         cin>>a>>b;
58         a++,b++;
59         u[a].push_back(b),u[b].push_back(a);
60         f[a].push_back(i),f[b].push_back(i);
61     }
62     vt[1]=true;
63     Tarjan(1,0);
64     //for(int i=1;i<=n;i++)cout<<anc[i]<<endl;
65     for(int i=1;i<=m;i++)
66         cout<<w[i]<<endl;
67 }