HDU2586（tarjanLCA板子）

 1 const int maxn = 4e4 + 5;
 2 int T, n, m;
 3 int f[maxn], vis[maxn], dis[maxn], ans[maxn];
 4 vector<P> vc[maxn];
 5 vector<int> query[maxn], id[maxn];
 6 
 7 inline int getf(int v) { return v == f[v] ? v : f[v] = getf(f[v]); }
 8 
 9 inline void Tarjan(int cur) {
10     vis[cur] = 1;
11 
12     for (auto son : vc[cur]) {
13         if (vis[son.first])    continue;
14 
15         dis[son.first] = dis[cur] + son.second;
16         Tarjan(son.first);
17         f[son.first] = cur;
18     }
19 
20     vis[cur] = 2;
21 
22     for (int i = 0; i < query[cur].size(); i++) {
23         int v = query[cur][i], t = id[cur][i];
24 
25         if (vis[v] == 2) {
26             int lca = getf(v);
27             ans[t] = dis[cur] + dis[v] - 2 * dis[lca];
28         }
29     }
30 }
31 
32 int main() {
33     for (read(T); T; T--) {
34         read(n), read(m);
35 
36         rep(i, 1, n) {
37             vc[i].clear(), query[i].clear(), id[i].clear();
38             f[i] = i, vis[i] = 0;
39         }
40 
41         rep(i, 1, n - 1) {
42             int u, v, cost;
43             read(u), read(v), read(cost);
44             vc[u].push_back({v, cost});
45             vc[v].push_back({u, cost});
46         }
47 
48         auto Add_Query = [](int u, int v, int i) {
49             query[u].push_back(v);
50             id[u].push_back(i);
51         };
52 
53         rep(i, 1, m) {
54             int u, v;
55             read(u), read(v);
56             Add_Query(u, v, i);
57             if(u != v)    Add_Query(v, u, i);
58         }
59 
60         Tarjan(1);
61 
62         rep(i, 1, m)
63             writeln(ans[i]);
64     }
65     return 0;
66 }