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

#include<iostream> 
#include<cstdio> 
#include<cmath>
#include<queue>
#include<vector>
#include<string.h>
#include<cstring>
#include<algorithm>
#include<set>
#include<map>
#include<fstream>
#include
 
<cstdlib>
#include<ctime>
#include<list>
#include<climits>
#include<bitset>
using namespace std;
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fopen freopen("input.txt", "r", stdin);freopen("output.txt", "w", stdout);
#define scd(a) scanf("%d",&a)
#define
 
 scf(a) scanf("%lf",&a)
#define scl(a) scanf("%lld",&a)
#define sci(a) scanf("%I64d",&a)
#define scs(a) scanf("%s",a)
#define left asfdasdasdfasdfsdfasfsdfasfdas1
#define tan asfdasdasdfasdfasfdfasfsdfasfdas
typedef long long ll;
typedef unsigned int un;
const int desll[4][2]={{0,1},{0,-1},{1
 
,0},{-1,0}};
const ll mod=1e9+7;
const int maxn=4e4+7;
const int maxm=3e8+7;
const double eps=1e-4;
int m,n;

struct node
{
    int b,nex,c;
}no[maxn*2];
int head[maxn],sz=0;
int add(int a,int b,int c){
    no[sz].b=b;
    no[sz].c=c;
    no[sz].nex=head[a];
    head[a]=sz++;
}
int father[maxn],tan[maxn*2][30],dep[maxn];
int ar[maxn*2],le,in[maxn];
ll dis[maxn];
void dfs1(int u,int pre){
    for(int i=head[u];i!=-1;i=no[i].nex){
        int v=no[i].b;
        if(v==pre)continue;
        dis[v]=dis[u]+no[i].c;
        father[v]=u;
        dep[v]=dep[u]+1;
        ar[le++]=u;
        dfs1(v,u);
    }
    in[u]=le;
    ar[le++]=u;
}
void init()
{
    memset(tan,0,sizeof(tan));
    for(int i=0;i<le;i++){
        tan[i][0]=ar[i];
    }
    for(int j=1;j<20;j++){
        for(int i=le-1;i>=0;i--){
            if(i+(1<<j)-1>=le)continue;
            int x=tan[i][j-1],y=tan[i+(1<<(j-1))][j-1];
            if(dep[x]<dep[y])tan[i][j]=x;
            else tan[i][j]=y;
            //cout<<i<<" "<<j<<" "<<tan[i][j]<<endl;
        }
    }
}
int sameFather(int a,int b)
{
    a=in[a];
    b=in[b];
    if(a>b)swap(a,b);
    int res=floor(log(b-a+1)/log(2));
    int x=tan[a][res],y=tan[b-(1<<res)+1][res];
    if(dep[x]<dep[y])return x;
    else return y;
}

int main()
{
    int t;scd(t);
    while(t--){
        scd(n);scd(m);
        memset(head,-1,sizeof(head));sz=0;
        for(int i=1;i<n;i++){
            int a,b,c;
            scd(a);scd(b);scd(c);
            add(a,b,c);
            add(b,a,c);
        }
        memset(dis,0,sizeof(dis));
        memset(dep,0,sizeof(dep));
        dep[1]=1;
        dfs1(1,0);
        father[1]=0;
        init();
        for(int i=0;i<m;i++){
            int a,b;
            scd(a);scd(b);
            int x=sameFather(a,b);
            printf("%d\n",dis[a]+dis[b]-2*dis[x]);
        }
    }
    return 0;
}

lca最短公共祖先模板（hdu2586）