http://acm.hdu.edu.cn/showproblem.php?pid=2586

题解：LCA

参考文章：https://www.cnblogs.com/JVxie/p/4854719.html

https://blog.csdn.net/weixin_43272781/article/details/88797088

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
#define endl "\n"
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q,w,v,u;
int ans,cnt,flag,temp,sum;
int pre[N];
bool vis[N];
int dep[N];
int ANS[N];
char str;
struct node{
    int v,w;
}x,tmp;
struct query{
    int u,v,id;
}e[N],y;
vector<node>G[N];
vector<query>Q[N];
int find(int x){return pre[x]==x?x:pre[x]=find(pre[x]);}
void marge(int u,int v){
    int tu=find(u);
    int tv=find(v);
    if(tu!=tv){
        pre[tv]=tu;
    }
}
void Tarjan(int u){//marge和find为并查集合并函数和查找函数
    //cout<<u<<endl;
    vis[u]=1;
    for(int i=0,j=G[u].size();i<j;i++) {   //访问所有u子节点v
        int v=G[u][i].v;
        if(vis[v])
            continue;
        dep[v]=dep[u]+G[u][i].w;
        Tarjan(v);        //继续往下遍历
        marge(u,v);    //合并v到u上
        //cout<<dep[v]<<endl;
    }
    for(int i=0,j=Q[u].size();i<j;i++){ //访问所有和u有询问关系的e
        int e=Q[u][i].v;
        if(vis[e]){
            //ANS[Q[u][i].id]=find(e);//u,e的最近公共祖先为find(e);
            int lca=find(e);
            //cout<<lca<<endl;
            ANS[Q[u][i].id]=min( ANS[Q[u][i].id],dep[u]+dep[e]-2*dep[lca]);
        }
    }
}
void init(){
    for(int i=1;i<=n;i++){
        pre[i]=i;
        G[i].clear();
        Q[i].clear();
    }
    memset(vis,0,sizeof(vis));
    memset(dep,0,sizeof(dep));
    memset(ANS,0x3f,sizeof(ANS));

}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&n,&m);
        init();
        for(int i=1;i<n;i++){
            scanf("%d%d%d",&u,&v,&k);
            x.v=v;
            x.w=k;
            G[u].push_back(x);
            x.v=u;
            G[v].push_back(x);
        }
        for(int i=1;i<=m;i++){
            scanf("%d%d",&u,&v);
            y.v=v;
            y.id=i;
            Q[u].push_back(y);
            y.v=u;
            Q[v].push_back(y);
        }
        Tarjan(1);
        for(int i=1;i<=m;i++){
            cout<<ANS[i]<<endl;
            //cout<<<<endl;
        }
        //cout<<endl;
    }

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}