35分TLE求助

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<iomanip>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<sstream>
#include<cctype>
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<ctime>
#define ll long long
#define ull unsigned long long
#define ff first
#define ss second
#define rep(i,a,b) for(register int i=(a);i<=(b);i++)
#define per(i,a,b) for(register int i=(a);i>=(b);i--)
using namespace std;
const int INF=2147483647;
inline int read()
{
	int x=0,k=1;char c=getchar();
	while(c<'0'||c>'9'){if(c=='-')k=-1;c=getchar();}
	while(c>='0'&&c<='9'){x=(x<<3)+(x<<1)+(c^48);c=getchar();}
	return x*k;
}
struct edge{
	int u,v,next;
}e[500086];
int n,m,head[500086],a,b,num=0,low[10086],dfn[10086],tot=0,st[10086],top=0,col[10086],color=0,cnt[10086],out[10086];
bool vis[10086];
inline void store(int x,int y)
{
	e[num++].u=x,e[num].v=y;
	e[num].next=head[x];
	head[x]=num;
}
inline void tarjan(int u)
{
	low[u]=dfn[u]=++tot;
	st[top++]=u;
	vis[u]=true;
	for(int i=head[u];i;i=e[i].next)
	{
		int t=e[i].v;
		if(!dfn[t])
		{
			tarjan(t);
			low[u]=min(low[u],low[t]);
		}
		else if(vis[t])
		{
			low[u]=min(low[u],dfn[t]);
		}
	}
	int ts;
	if(low[u]==dfn[u])
	{
		++color;
		do
		{
			ts=st[--top];
			vis[ts]=false;
			col[ts]=color;
			cnt[color]++;
		}while(ts!=u);
	}
}
int main()
{
	n=read(),m=read();
	rep(i,1,m)
	{
		a=read(),b=read();
		store(a,b);
	}
	rep(i,1,n)
	{
		if(!dfn[i])tarjan(i);
	}
	rep(i,1,n)
	{
		for(int j=head[i];j;j=e[i].next)
		{
			int v=e[j].v;
			if(col[i]!=col[v])out[col[i]]++;
		}
	}
	int luck=0;
	rep(i,1,color)
	{
		if(!out[i])
		{
			if(luck){
				printf("0");
				return 0;
			}
			luck=i;
		}
	}
	printf("%d",cnt[luck]);
	return 0;
}