bzoj1654 / P2863 [USACO06JAN]牛的舞会The Cow Prom

P2863 [USACO06JAN]牛的舞会The Cow Prom

求点数$>1$的强连通分量数，裸的Tanjan模板。

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 using namespace std;
 int min(int &a,int &b){return a<b?a:b;}
 #define N 10002
 #define M 50002
 int n,m,clo,dfn[N],low[N],blo,be[N],tp,st[N],ans;
 int cnt,hd[N],nxt[M<<],ed[N],poi[M<<];
 void adde(int x,int y){
     nxt[ed[x]]=++cnt; hd[x]=hd[x]?hd[x]:cnt;
     ed[x]=cnt; poi[cnt]=y;
 }
 void tarjan(int x){
     dfn[x]=low[x]=++clo; st[++tp]=x;
     for(int i=hd[x];i;i=nxt[i]){
         int to=poi[i];
         if(!dfn[to]){
             tarjan(to);
             low[x]=min(low[x],low[to]);
         }else if(!be[to]) low[x]=min(low[x],dfn[to]);
     }
     if(dfn[x]<=low[x]){
         int tot=;
         be[x]=++blo;
         while(st[tp]!=x) be[st[tp--]]=blo,++tot;
         --tp; ans+=(tot>);
     }
 }
 int main(){
     scanf("%d%d",&n,&m);
     for(int i=,q1,q2;i<=m;++i)
         scanf("%d%d",&q1,&q2),adde(q1,q2);
     for(int i=;i<=n;++i) if(!dfn[i]) tarjan(i);
     printf("%d",ans);
     return ;
 }