【HDOJ6604】Blow up the city（支配树）

题意：给定一个n点m边的DAG，将只有入边的点称为周驿东点

q次询问，每次给定a,b两点，询问删去某个点x和其相连的所有边，能使a,b至少其中之一不能到达任何周驿东点的x的个数

n,q<=1e5，m<=2e5

思路：

 #include<bits/stdc++.h>
 using namespace std;
 typedef long long ll;
 typedef unsigned int uint;
 typedef unsigned long long ull;
 typedef pair<int,int> PII;
 typedef pair<ll,ll> Pll;
 typedef vector<int> VI;
 #define N  210000
 #define M  1100000
 #define fi first
 #define se second
 #define MP make_pair
 #define pi acos(-1)
 #define mem(a,b) memset(a,b,sizeof(a))
 #define rep(i,a,b) for(int i=(int)a;i<=(int)b;i++)
 #define per(i,a,b) for(int i=(int)a;i>=(int)b;i--)
 #define lowbit(x) x&(-x)
 #define Rand (rand()*(1<<16)+rand())
 #define id(x) ((x)<=B?(x):m-n/(x)+1)
 #define ls p<<1
 #define rs p<<1|1

 const ll MOD=,inv2=(MOD+)/;
       double eps=1e-;
       ll INF=1e14;

 vector<int> dom[N],be[N];
 int f[N][],head[N],vet[N],nxt[N],dep[N],ind[N],
     id[N],semi[N],p[N],pa[N],dfn[N],idom[N],mn[N],tot,cnt;

 int read()
 {
    int v=,f=;
    char c=getchar();
    while(c<||<c) {if(c=='-') f=-; c=getchar();}
    while(<=c&&c<=) v=(v<<)+v+v+c-,c=getchar();
    return v*f;
 }

 void add(int a,int b)
 {
     nxt[++tot]=head[a];
     vet[tot]=b;
     head[a]=tot;
 }

 void dfs(int u)
 {
     dfn[u]=++cnt; id[cnt]=u;
     int e=head[u];
     while(e)
     {
         int v=vet[e];
         if(!dfn[v])
         {
             dfs(v);
             pa[dfn[v]]=dfn[u];
         }
         be[dfn[v]].push_back(dfn[u]);
         e=nxt[e];
     }
 }

 int get(int x)
 {
     if(p[x]!=p[p[x]])
     {
         if(semi[mn[x]]>semi[get(p[x])]) mn[x]=get(p[x]);
         p[x]=p[p[x]];
     }
     return mn[x];
 }

 void LT()
 {
     per(i,cnt,)
     {
         for(int j:be[i]) semi[i]=min(semi[i],semi[get(j)]);
         dom[semi[i]].push_back(i);
         int x=p[i]=pa[i];
         for(int y:dom[x]) idom[y]=(semi[get(y)]<x?get(y):x);
         dom[x].clear();
     }
     rep(i,,cnt)
     {
         if(idom[i]!=semi[i]) idom[i]=idom[idom[i]];
         dom[id[idom[i]]].push_back(id[i]);
     }
 }

 void getdep(int u,int fa)
 {
     rep(i,,) f[u][i]=f[f[u][i-]][i-];
     int e=head[u];
     while(e)
     {
         int v=vet[e];
         if(v!=fa)
         {
             f[v][]=u;
             dep[v]=dep[u]+;
             getdep(v,u);
         }
         e=nxt[e];
     }
 }

 int lca(int x,int y)
 {
     if(dep[x]<dep[y]) swap(x,y);
     int d=dep[x]-dep[y];
     rep(i,,)
      if((d>>i)&) x=f[x][i];
     per(i,,)
      if(f[x][i]!=f[y][i])
      {
          x=f[x][i];
          y=f[y][i];
      }
     if(x==y) return x;
     return f[x][];
 }

 int main()
 {
     //freopen("1.in","r",stdin);
     //freopen("1.out","w",stdout);
     int cas=read();
     while(cas--)
     {
         int n=read(),m=read();
         tot=;
         rep(i,,n+) head[i]=ind[i]=dfn[i]=id[i]=idom[i]=;
         rep(i,,m)
         {
             int x=read(),y=read();
             add(y,x);
             ind[x]++;
         }
         int root=n+;
         rep(i,,n)
          if(!ind[i]) add(root,i);
         rep(i,,root)
         {
             dfn[i]=;
             dom[i].clear();
             be[i].clear();
             p[i]=mn[i]=semi[i]=i;
         }
         cnt=;
         dfs(root);
         LT();
         tot=;
         rep(i,,root) head[i]=;
         rep(i,,root)
          if(id[idom[i]]) add(id[idom[i]],id[i]);
         rep(i,,root) dep[i]=;
         getdep(root,);
         int q=read();
         while(q--)
         {
             int x=read(),y=read();
             int t=lca(x,y);
             printf("%d\n",dep[x]+dep[y]-dep[t]);
         }
     }

     return ;
 }