hdu 2586 (lca-RMQ)

 #include <iostream>
 #include <cstdlib>
 #include <cstring>
 #include <queue>
 #include <cstdio>
 #include <algorithm>
 #include <map>
 #define LL long long

 using namespace std;
 const int N = 5e4;

 int head[N],tot;
 int sum,dir[N],ver[N*],R[N*],first[N],visit[N];
 int dp[*N][];
 struct nodes
 {
     int to,next,w;
 }Edge[N];

 void E_init()
 {
     tot = ;
     memset(head,-,sizeof(head));
 }

 void add(int u,int v,int w)
 {
     Edge[tot].to = v;
     Edge[tot].w = w;
     Edge[tot].next = head[u];
     head[u] = tot++;
 }

 void dfs(int u,int dep)
 {
     visit[u] = ;
     ver[++sum] = u;
     first[u] = sum;
     R[sum] = dep;
     for(int i = head[u]; i != -; i = Edge[i].next)
     {
         if(!visit[Edge[i].to])
         {
             dir[Edge[i].to] = dir[u]+Edge[i].w;
             dfs(Edge[i].to,dep+);
             ver[++sum] = u;
             R[sum] = dep;
         }
     }
 }

 void ST(int n)
 {
     for(int i = ; i <= n; i++)
         dp[i][] = i;
     for(int j = ; (<<j)<=n; j++)
     {
         for(int i = ;i+(<<j)-<=n; i++)
         {
             int l,r;
             l = dp[i][j-];
             r = dp[i+ (<<(j-))][j-];
             dp[i][j] = R[l]<R[r]?l:r;
         }
     }
 }

 int RMQ(int l,int r)
 {
    //int k = log(r-l+1)/log(2);
    int k = ;
    while( (<<(k+)) <= r - l + ) k++;
    int ll = dp[l][k], rr = dp[r-(<<k)+][k];
    return R[ll]<R[rr]?ll:rr;
 }

 int LCA(int u,int v)
 {
     int x = first[u],y = first[v];
     if(x > y) swap(x,y);
     return ver[RMQ(x,y)];
 }

 void solve()
 {
     int n,q;
     scanf("%d %d",&n,&q);
     E_init();
     for(int i = ; i < n-; i++)
     {
         int u,v,w;
         scanf("%d %d %d",&u,&v,&w);
         add(u,v,w);
         add(v,u,w);
     }
     memset(visit,,sizeof(visit));
     sum = ;
     dir[] = ;

     dfs(,);
     ST(n*-);

     while(q--)
     {
         int a,b,c;
         scanf("%d %d",&a,&b);
         c = LCA(a,b);
         printf("%d\n",dir[a]+dir[b]-*dir[c]);
     }

 }

 int main(void)
 {
     int t;
     scanf("%d",&t);
     while(t--)
     {
         solve();
     }
     return ;
 }