HDU2586

#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdio>
#include <cstring>
using namespace std;

const int MAXN = 40000 + 10;
struct Edge{
int to,cost;
Edge(){};
Edge(int _to,int _cost)
:to(_to),cost(_cost){};
};

vector<Edge> tree[MAXN];
vector<Edge> Qes[MAXN];
int degree[MAXN];
int f[MAXN];
bool vst[MAXN];
int dist[MAXN];
int ancestor[MAXN];
int ans[MAXN];
int rank[MAXN];
int N,M;

void init(){
for(int i = 0;i <= N;++i){
degree[i] = 0;
f[i] = i;
ans[i] = -1;
rank[i] = 0;
dist[i] = 0;
vst[i] = false;
ancestor[i] = -1;
tree[i].clear();
Qes[i].clear();
}
}

int Find(int x){
if(x == f[x])
return x;
return f[x] = Find(f[x]);
}

void LCA(int u){
int sz = tree[u].size();
for(int i = 0;i < sz;++i){
Edge& e = tree[u][i];
if(!vst[e.to]){
vst[e.to] = 1;
dist[e.to] = dist[u] + e.cost;
LCA(e.to);
f[e.to] = u;
int k = Qes[e.to].size();
for(int j = 0;j < k;++j){
Edge& et = Qes[e.to][j];
if(vst[et.to]&&ans[et.cost] == -1){  //还未遍历到
if(et.to == e.to) ans[et.cost] = 0;
else ans[et.cost] = dist[e.to] + dist[et.to] - 2*dist[Find(et.to)];
}
}
}
}
}

int main()
{
int T;
scanf("%d",&T);
while(T--){
scanf("%d%d",&N,&M);
init();
int x,y,c;
for(int i = 1;i < N;++i){
scanf("%d%d%d",&x,&y,&c);
tree[x].push_back(Edge(y,c));
tree[y].push_back(Edge(x,c));
}

for(int i = 0;i < M;++i){
scanf("%d%d",&x,&y);
Qes[x].push_back(Edge(y,i));
Qes[y].push_back(Edge(x,i));
}

vst[1] = 1;
LCA(1);

for(int i = 0;i < M;++i){
printf("%d\n",ans[i]);
}
}
return 0;
}