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=200005,M=800005;
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,0,sizeof p);
    memset(P,0,sizeof P);
    memset(dfn,0,sizeof dfn);
    memset(low,0,sizeof low);
    memset(imp,0,sizeof imp);
    memset(top,0,sizeof top);
    for(int i=1;i<=c;i++) pbc[i].clear();
    cnt=Cnt=tot=c=0;
}
void RTPBC(int nde)
{
    int tmp=0;
    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>1) 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=0;
    siz[nde]=1,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+1),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]-2*dis[lca];
}
int main()
{
    scanf("%d",&T);
    while(T--)
    {
        Init();
        scanf("%d%d",&n,&m);
        for(int i=1;i<=m;i++)
            scanf("%d%d",&t1,&t2),Link(t1,t2);
        RTPBC(rt=1);
        for(int i=1;i<=c;i++)
            for(vit it=pbc[i].begin();it!=pbc[i].end();it++) Linka(*it,n+i);
        tot=0,DFS(1,0,1),Mark(1,1);
        scanf("%d",&q);
        while(q--)
        {
            scanf("%d",&o); int ans=0;
            for(int i=1;i<=o;i++) scanf("%d",&qry[i]);
            sort(qry+1,qry+1+o,cmp),qry[++o]=qry[1];
            for(int i=2;i<=o;i++) ans+=Dist(qry[i],qry[i-1]);
            printf("%d
",(ans>>1)-o+1+(LCA(qry[o],qry[o-1])<=n));
        }
    }
    return 0;
}