AC代码：

#include<bits/stdc++.h>
#define int long long
using namespace std;
inline int read(){
	int x=0,f=1;char c=getchar();
	while(c<'0'||'9'<c){if(c=='-')f=-1;c=getchar();}
	while('0'<=c&&c<='9'){x=(x<<1)+(x<<3)+c-'0';c=getchar();}
	return x*f;
}
const int N=1005,M=10005;
struct edge{
	int v,nxt;
}ed[M];
int en,first[N];
int k,n,m,ans,f[N];
bool vis[N];
void add(int u,int v){
	ed[++en]=(edge){v,first[u]};
	first[u]=en;
}
queue<int>q,qwq;
signed main(){
	k=read();n=read();m=read();
	for(int i=1;i<=k;i++)qwq.push(read());
	for(int i=1;i<=m;i++){
		int x=read(),y=read();
		add(x,y);
	}
	while(!qwq.empty()){
		memset(vis,0,sizeof(vis));
		int x=qwq.front();qwq.pop();
		q.push(x);vis[x]=1;
		while(!q.empty()){
			int u=q.front();q.pop();f[u]++;
			for(int i=first[u];i;i=ed[i].nxt)
				if(!vis[ed[i].v])
					vis[ed[i].v]=1,q.push(ed[i].v);
		}
	}
	for(int i=1;i<=n;i++)
		if(f[i]==k)ans++;
	printf("%lld",ans);
	return 0;
}

WA代码：

#include<bits/stdc++.h>
#define int long long
using namespace std;
inline int read(){
	int x=0,f=1;char c=getchar();
	while(c<'0'||'9'<c){if(c=='-')f=-1;c=getchar();}
	while('0'<=c&&c<='9'){x=(x<<1)+(x<<3)+c-'0';c=getchar();}
	return x*f;
}
const int N=1005,M=10005;
struct edge{
	int v,nxt;
}ed[M];
int en,first[N];
int k,n,m,ans,f[N];
bool vis[N];
void add(int u,int v){
	ed[++en]=(edge){v,first[u]};
	first[u]=en;
}
queue<int>q,qwq;
signed main(){
	k=read();n=read();m=read();
	for(int i=1;i<=k;i++)qwq.push(read());
	for(int i=1;i<=m;i++)
		add(read(),read());
	while(!qwq.empty()){
		memset(vis,0,sizeof(vis));
		int x=qwq.front();qwq.pop();
		q.push(x);vis[x]=1;
		while(!q.empty()){
			int u=q.front();q.pop();f[u]++;
			for(int i=first[u];i;i=ed[i].nxt)
				if(!vis[ed[i].v])
					vis[ed[i].v]=1,q.push(ed[i].v);
		}
	}
	for(int i=1;i<=n;i++)
		if(f[i]==k)ans++;
	printf("%lld",ans);
	return 0;
}

仅读入时不一样，但是第二份50