这个遍历停止条件为什么不是i!=-1再把head全设置为-1,否则编号为0的边不能被遍历到

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
inline int read(){
	register int x=0,v=1,ch=getchar();
	while(!isdigit(ch)){if(ch=='-')v=-1;ch=getchar();}
	while(isdigit(ch)){x=(x<<3)+(x<<1)+(ch^'0');ch=getchar();}
	return x*v;
}
const int MAX=1005,N=10005;
int k,n,m;
struct Edge{
	int e,next;
}e[N];
int head[MAX],cnt;
inline void add(int u,int v){
	e[cnt].e=v;
	e[cnt].next=head[u];
	head[u]=cnt++;
}
int u,v,Ans=0;bool f[MAX],vis[MAX];
void dfs(int now){
	vis[now]=1;
	for(register int i=head[now];i;i=e[i].next){
		if(!vis[e[i].e])dfs(e[i].e);
	}
}
int main(){
	k=read(),n=read(),m=read();
	for(register int i=1;i<=k;++i){
		f[read()]=1;
	}
	for(register int i=1;i<=m;++i){
		u=read(),v=read();
		add(v,u);
	}
	for(register int i=1;i<=n;++i){
		memset(vis,0,sizeof(vis));
		dfs(i);
		for(register int j=1;j<=n;++j){
			if(vis[j]!=1&&f[j]==1){
				goto end;	
			}
		}
		++Ans;
		end:;
	}
	printf("%d\n",Ans);
	return 0;
}