What is Test #16? Please someone help!

Same here... got stuck in Test-16 .

so why did you get the WA16?

Well maybe someone gonna read this but i got WA #16 cause my logic was wrong.
i thought that i need to check if i studied any of prerequisite BUT i must check if i studied ALL OF them.
maybe my code would help idk

#include <iostream>
#include <vector>
using namespace std;

int N, M, a[(int)1e3 + 5], b, c;
bool visited[(int)1e3 + 5], flag, ans = true;
vector <vector <int> > adj((int)1e3 + 5);
int main()
{
    cin >> N >> M;
    while(M--)
        cin >> b >> c, adj[c].push_back(b);
    for(int i = 0; i < N;++i)
    {
        cin >> a[i];
        flag = true;
        visited[a[i]] = true;
        if(adj[a[i]].empty()) continue;
        for(int j = 0; j < adj[a[i]].size();++j)
            if(!visited[adj[a[i]][j]])
                flag = false;
        if(!flag)
            ans = false;
    }
    if(!ans)
        cout <<"NO";
    else
        cout << "YES";
}