求助48pts玄关

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1e4+5;
struct node{
	int nt,end;
}edge[50005];
int cnt,head[N];
void add(int u,int v){
	cnt++;
	edge[cnt].nt=head[u];
	head[u]=cnt;
	edge[cnt].end=v;
}
int dfn[N],low[N],vis[N],co[N],tot,col;
stack<int> stk;
void tarjan(int u){
	dfn[u]=low[u]=++tot;
	stk.push(u);
	vis[u]=1;
	for(int i=head[u];i;i=edge[i].nt){
		int v=edge[i].end;
		if(dfn[v]==0){
			tarjan(v);
			low[u]=min(low[u],low[v]);
		}else if(vis[v]==1){
			low[u]=min(low[u],low[v]);
		}
	}
	if(dfn[u]==low[u]){
		co[u]=++col;
		while(stk.top()!=u){
			co[stk.top()]=col;
			vis[stk.top()]=0;
			stk.pop();
		}
		vis[u]=0;
		stk.pop();
	}
	return ;
}
int n,m,u,v;
int number[N],fan[N],ans;
signed main(){
	scanf("%lld%lld",&n,&m);
	for(int i=1;i<=m;i++){
		scanf("%lld%lld",&u,&v);
		add(u,v);
	}
	for(int i=1;i<=n;i++){
		if(!dfn[i])tarjan(i);
	}
	for(int i=1;i<=n;i++){
		number[co[i]]++;
		fan[co[i]]++;
	}
	for(int i=1;i<=n;i++){
		for(int j=head[i];j;j=edge[j].nt){
			int v=edge[j].end;
			if(co[i]!=co[v])fan[co[v]]+=number[co[i]];
		}
	}
	for(int i=1;i<=n;i++){
		if(fan[co[i]]==n)ans++;
	}
	printf("%lld",ans);
	return 0;
}