LCA

#include <iostream>#include<algorithm>#include<stdio.h>#include<string.h>#include<cmath>using namespace std;const int maxn=40010;struct node{    int to,next,w;}edge[maxn<<1];int head[maxn],cnt;void addedge(int u,int v,int we){    edge[cnt].to=v ; edge[cnt].next=head[u];    edge[cnt].w=we;  head[u]=cnt++;}bool vis[maxn];int dis[maxn];int deep[maxn<<1];int ver[maxn<<1];int pos[maxn];int tot=0;void dfs(int u,int step){    vis[u]=true;    ver[++tot]=u;pos[u]=tot;deep[tot]=step;    for(int i=head[u];i!=-1;i=edge[i].next)    {        int v=edge[i].to;        int w=edge[i].w;        if(!vis[v])        {            dis[v]=dis[u]+w;            dfs(v,step+1);            ver[++tot]=u,deep[tot]=step;        }    }}int dp[maxn<<1][30];void st(int n){    int k=(int)(log((double)n)/log(2.0));    for(int i=1;i<=n;i++) dp[i][0]=i;    for(int j=1;j<=k;j++)    {        for(int i=1;i+(1<<j)-1<=n;++i)        {            int x=dp[i][j-1],y=dp[i+(1<<(j-1))][j-1];            if(deep[x]<deep[y]) dp[i][j]=x;  else dp[i][j]=y;        }    }}int lca(int x,int y){    int a=pos[x],b=pos[y];    if(a>b) swap(a,b);    int k=(int)(log((double)(b-a+1))/log(2.0));    int l=dp[a][k],r=dp[b-(1<<k)+1][k];    return deep[l]<deep[r] ? ver[l]: ver[r];}void init(){   cnt=0; tot=0;   memset(head,-1,sizeof(head));   memset(vis,0,sizeof(vis));   memset(dis,0,sizeof(dis));}int main(){    int T;    scanf("%d",&T);    while(T--)    {        init();        int n,m;        scanf("%d%d",&n,&m);        for(int i=1;i<n;++i)        {            int u,v,w;            scanf("%d%d%d",&u,&v,&w);            addedge(u,v,w);            addedge(v,u,w);        }        dfs(1,1); st(tot);        while(m--)        {           int u,v;           scanf("%d%d",&u,&v);           long long ans=dis[u]+dis[v]-2*dis[lca(u,v)];           printf("%I64d\n",ans);        }    }    return 0;}