Tarjan缩点【模板】

 #include <algorithm>
 #include <cstdio>
 #include <map>

 using namespace std;

 const int N();
 map<int,bool>Map[N];
 int n,m,v,u;
 int edgesum,head[N];
 int edgesum2,head2[N];

 struct Edge
 {
     int from,to,next;
     Edge(int from=,int to=,int next=) :
         from(from),to(to),next(next) {}
 }edge[N],edge2[N];
 int ins(int from,int to)
 {
     edge[++edgesum]=Edge(from,to,head[from]);
     return head[from]=edgesum;
 }

 int ins2(int from,int to)
 {
     edge2[++edgesum2]=Edge(from,to,head2[from]);
     return head2[from]=edgesum2;
 }

 int dfn[N],tim,low[N],vis[N];
 int Stack[N],top,instack[N];
 int col[N],colsum;

 void DFS(int now)
 {
     dfn[now]=low[now]=++tim; vis[now]=;
     Stack[++top]=now; instack[now]=;
     for(int i=head[now];i;i=edge[i].next)
     {
         int to=edge[i].to;
         if(instack[to]) low[i]=min(low[i],dfn[to]);
         else if(!vis[to])
                 DFS(to),low[i]=min(low[i],low[to]);
     }
     if(low[now]==dfn[now])
     {
         colsum++;
         col[now]=colsum;
         for(;Stack[top]!=now;top--)
         {
             col[Stack[top]]=colsum;
             instack[Stack[top]]=;
         }
         instack[now]=;
         top--;
     }
 }

 int main()
 {
     scanf("%d%d",&n,&m);
     for(;m--;)
     {
         scanf("%d%d",&u,&v);
         ins(u,v);
     }
     for(int i=;i<=n;i++)
         if(!vis[i]) DFS(i);
     for(int i=;i<=n;i++)
       for(int u=head[i];u;u=edge[i].next)
       {
           int v=edge[i].to;
             if(col[i]!=col[v])
                 if(Map[col[i]].find(col[v])==Map[col[i]].end())
                 {
                     Map[col[i]][col[v]]=;
                     ins2(col[i],col[v]);
             }
       }
     return ;
 }