problema spectacolelor greedy

#include<iostream>
#include<fstream>
using namespace std;
int n,m,s[20];
struct activ
{   int x,y,z;
};
activ a[20],aux;
void citire(int &n)
{   ifstream f("e:\\info\\greedy\\spectacol.txt");
    f>>n;
    for(int i=1;i<=n;i++)
        f>>a[i].x>>a[i].y>>a[i].z;
    f.close();
}
void afisare()
{   for(int i=1;i<=n;i++)
    {   cout<<a[i].x<<" "<<a[i].y<<" "<<a[i].z;
        cout<<endl;
    }
}
void sortare()
{   activ aux;
    for(int i=1;i<n;i++)
        for(int j=i+1;j<=n;j++)
            if(a[i].z>a[j].z)
            {   aux=a[i];
                a[i]=a[j];
                a[j]=aux;
            }
}
void greedy(int &m)
{   int j=1;s[1]=1;
    for(int i=2;i<=n;i++)
        if(a[i].y>=a[s[j]].z)
        {   j++;
            s[j]=i;
        }
    m=j;
}
void afis()
{   for(int i=1;i<=m;i++)
        cout<<"activitatea "<<a[s[i]].x<<" ora de inceput "<<a[s[i]].y<<" ora de sfarsit "<<a[s[i]].z<<endl;
}
int main()
{   citire(n);
    afisare();
    cout<<endl;
    sortare();
    afisare();
    cout<<endl;
    greedy(m);
    afis();

}
8
1 9 11
2 12 13
3 8 10
4 10 12
5 16 18
6 14 16
7 20 22
8 19 21