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<<1],ed[N],poi[M<<1];
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=1;
        be[x]=++blo;
        while(st[tp]!=x) be[st[tp--]]=blo,++tot;
        --tp; ans+=(tot>1);
    }
}
int main(){
    scanf("%d%d",&n,&m);
    for(int i=1,q1,q2;i<=m;++i)
        scanf("%d%d",&q1,&q2),adde(q1,q2);
    for(int i=1;i<=n;++i) if(!dfn[i]) tarjan(i);
    printf("%d",ans);
    return 0;
}