#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
    int N,M,a,b;
    vector <int> t;
    vector <int> s;
    vector <int> st;
    cin>>N;
    for(int i=0; i<N; i++)
    {
        cin>>a;
        t.push_back(a);
    }
    cin>>M;
    for(int i=0; i<M; i++)
    {
        cin>>b;
        s.push_back(b);
    }
    for(int i=0; i<M; i++)
    {
        for(int j=0; j<N; j++)
        {
            if(s[i]==t[j])  st.push_back(s[i]);
        }
    }
    sort(st.begin(),st.end());
    cout<<st.size();
    return 0;
}

"Professor's list is sorted in non-descending order", so duplicates allowed.
You are pushing s[i] into out not once but as many times as equal numbers found in t.
Break internal cycle when first equality found.

But. After I fixed your code I received TLE 8 because of "N*M" complexity.
You must optimize perfomance (and should - memory usage).

Edited by author 20.04.2016 13:21

Edited by author 20.04.2016 13:21

but what can i do to solve TLE8

C.O. thinks you should optimize your program.

1) Remove s and st arrays. You can - read students value, check it, increase counter if necessary.

2) Speed up checking if date is in professor dates. You can use binary search over sorted array, std::set, std::unordered_set for example.

Now I have this code but I have compilation eror why?
#include <iostream>
#include <vector>
#include <set>
using namespace std;
int main()
{
    int N,M,a,b,counter=0;
    vector <int> t;
    set <int> s;
    cin>>N;
    for(int i=0; i<N; i++)
    {
        cin>>a;
        t.push_back(a);
    }
    cin>>M;
    for(int i=0; i<M; i++)
    {
        cin>>b;
        s.insert(b);
    }
    for(int i=0; i<s.size(); i++)
    {
        for(int j=0; j<t.size(); j++)
        {
            if(s[i])==t[j])  {counter++; break;}
        }
    }

    cout<<counter;
    return 0;
}