HDU2586（tarjanLCA板子）

 const int maxn = 4e4 + ;
 int T, n, m;
 int f[maxn], vis[maxn], dis[maxn], ans[maxn];
 vector<P> vc[maxn];
 vector<int> query[maxn], id[maxn];

 inline int getf(int v) { return v == f[v] ? v : f[v] = getf(f[v]); }

 inline void Tarjan(int cur) {
     vis[cur] = ;

     for (auto son : vc[cur]) {
         if (vis[son.first])    continue;

         dis[son.first] = dis[cur] + son.second;
         Tarjan(son.first);
         f[son.first] = cur;
     }

     vis[cur] = ;

     for (int i = ; i < query[cur].size(); i++) {
         int v = query[cur][i], t = id[cur][i];

         if (vis[v] == ) {
             int lca = getf(v);
             ans[t] = dis[cur] + dis[v] -  * dis[lca];
         }
     }
 }

 int main() {
     for (read(T); T; T--) {
         read(n), read(m);

         rep(i, , n) {
             vc[i].clear(), query[i].clear(), id[i].clear();
             f[i] = i, vis[i] = ;
         }

         rep(i, , n - ) {
             int u, v, cost;
             read(u), read(v), read(cost);
             vc[u].push_back({v, cost});
             vc[v].push_back({u, cost});
         }

         auto Add_Query = [](int u, int v, int i) {
             query[u].push_back(v);
             id[u].push_back(i);
         };

         rep(i, , m) {
             int u, v;
             read(u), read(v);
             Add_Query(u, v, i);
             if(u != v)    Add_Query(v, u, i);
         }

         Tarjan();

         rep(i, , m)
             writeln(ans[i]);
     }
     return ;
 }