[CSP]通信网络(链式前向星)

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define endl '\n'

const int N=1e3+5,M=2e4+5;

int n,m;
int res=0;
int head1[N],head2[N],cnt1,cnt2;
bool st1[N],st2[N];
struct node
{
	int v,next;
}edge1[M],edge2[M];
void addedge1(int u,int v)
{
	cnt1++;
	edge1[cnt1].v=v;
	edge1[cnt1].next=head1[u];
	head1[u]=cnt1; 
}
void addedge2(int u,int v)
{
	cnt2++;
	edge2[cnt2].v=v;
	edge2[cnt2].next=head2[u];
	head2[u]=cnt2; 
}
void dfs(int u,int head[],bool st[],node edge[])
{
	st[u]=1;
	for(int i=head[u];i;i=edge[i].next)
	{
		int j=edge[i].v;
		if(!st[j])dfs(j,head,st,edge);
	}
}
int main()
{
	cin>>n>>m;
	while(m--)
	{
		int a,b;cin>>a>>b;
		addedge1(a,b),addedge2(b,a);
	}
	int res=0;
	for(int i=1;i<=n;i++)
	{
		memset(st1,0,sizeof st1);
		memset(st2,0,sizeof st2);
		dfs(i,head1,st1,edge1);
		dfs(i,head2,st2,edge2);
		int s=0;
		for(int j=1;j<=n;j++)
		{
			if(st1[j]||st2[j])s++;
		}
		if(s==n)res++;
	}
	cout<<res<<endl;
}