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 ;

 }