解题：SDOI2018 战略游戏

题面

先圆方树然后建虚树，答案就是虚树大小。虚树没必要建出来，把原来的点的点权设为1，直接dfs序排序后相邻点求距离加上首尾两个点的距离，最后除以二(画一下可以发现是正反算了两遍)，注意还要去掉询问点和补上首尾两个点的LCA

 #include<cstdio>
 #include<vector>
 #include<cstring>
 #include<algorithm>
 #define vint vector<int>
 #define vit vector<int> ::iterator
 using namespace std;
 const int N=,M=;
 int T,n,m,c,q,o,t1,t2,rt,pt,cnt,Cnt,tot;
 int dfn[N],low[N],stk[N],isc[N],col[N];
 int p[N],noww[M],goal[M],P[N],Noww[M],Goal[M];
 int siz[N],dep[N],fth[N],imp[N],top[N],qry[M],dis[N]; vint pbc[N];
 void Link(int f,int t)
 {
     noww[++cnt]=p[f];
     goal[cnt]=t,p[f]=cnt;
     noww[++cnt]=p[t];
     goal[cnt]=f,p[t]=cnt;
 }
 void Linka(int f,int t)
 {
     Noww[++Cnt]=P[f];
     Goal[Cnt]=t,P[f]=Cnt;
     Noww[++Cnt]=P[t];
     Goal[Cnt]=f,P[t]=Cnt;
 }
 bool cmp(int a,int b)
 {
     return dfn[a]<dfn[b];
 }
 void Init()
 {
     memset(p,,sizeof p);
     memset(P,,sizeof P);
     memset(dfn,,sizeof dfn);
     memset(low,,sizeof low);
     memset(imp,,sizeof imp);
     memset(top,,sizeof top);
     for(int i=;i<=c;i++) pbc[i].clear();
     cnt=Cnt=tot=c=;
 }
 void RTPBC(int nde)
 {
     int tmp=;
     dfn[nde]=low[nde]=++tot,stk[++pt]=nde;
     for(int i=p[nde],g;i;i=noww[i])
         if(!dfn[g=goal[i]])
         {
             RTPBC(g),low[nde]=min(low[nde],low[g]);
             if(dfn[nde]<=low[g])
             {
                 if(nde!=rt||++tmp>) isc[nde]=true;
                 int tep; c++;
                 do
                 {
                     tep=stk[pt--],col[tep]=c;
                     pbc[c].push_back(tep);
                 }while(tep!=g);
                 pbc[c].push_back(nde);
             }
         }
         else low[nde]=min(low[nde],dfn[g]);
 }
 void DFS(int nde,int far,int dth)
 {
     int tmp=;
     siz[nde]=,fth[nde]=far,dep[nde]=dth;
     for(int i=P[nde],g;i;i=Noww[i])
         if((g=Goal[i])!=far)
         {
             dis[g]=dis[nde]+(g<=n);
             DFS(g,nde,dth+),siz[nde]+=siz[g];
             if(siz[g]>tmp) tmp=siz[g],imp[nde]=g;
         }
 }
 void Mark(int nde,int upt)
 {
     top[nde]=upt,dfn[nde]=++tot;
     if(imp[nde])
     {
         Mark(imp[nde],upt);
         for(int i=P[nde],g;i;i=Noww[i])
             if((g=Goal[i])!=fth[nde]&&g!=imp[nde]) Mark(g,g);
     }
 }
 int LCA(int x,int y)
 {
     while(top[x]!=top[y])
     {
         if(dep[top[x]]<dep[top[y]])
             swap(x,y); x=fth[top[x]];
     }
     return dep[x]<dep[y]?x:y;
 }
 int Dist(int x,int y)
 {
     int lca=LCA(x,y);
     return dis[x]+dis[y]-*dis[lca];
 }
 int main()
 {
     scanf("%d",&T);
     while(T--)
     {
         Init();
         scanf("%d%d",&n,&m);
         for(int i=;i<=m;i++)
             scanf("%d%d",&t1,&t2),Link(t1,t2);
         RTPBC(rt=);
         for(int i=;i<=c;i++)
             for(vit it=pbc[i].begin();it!=pbc[i].end();it++) Linka(*it,n+i);
         tot=,DFS(,,),Mark(,);
         scanf("%d",&q);
         while(q--)
         {
             scanf("%d",&o); int ans=;
             for(int i=;i<=o;i++) scanf("%d",&qry[i]);
             sort(qry+,qry++o,cmp),qry[++o]=qry[];
             for(int i=;i<=o;i++) ans+=Dist(qry[i],qry[i-]);
             printf("%d\n",(ans>>)-o++(LCA(qry[o],qry[o-])<=n));
         }
     }
     return ;
 }