排座椅不懂

#include<iostream>
#include<algorithm>
using namespace std;
struct A
{
    int n,p;
}k[1005],l[1005];
bool cmp(A x,A y)
{
    return x.n>y.n;
}
bool cmp1(A x,A y)
{
    return x.p<y.p;
}
int d,n,m,p,q,x1,x2,y1,y2,i1=0,j1=0;
int main()
{
    cin>>m>>n>>p>>q>>d;
    for(int i=1;i<=d;i++)
    {
        cin>>x1>>y1>>x2>>y2;
        if(x1==x2) 
        {
        l[min(y1,y2)].p=min(y1,y2);
        l[min(y1,y2)].n++;
        }
        else 
        {
        k[min(x1,x2)].p=min(x1,x2);
        k[min(x1,x2)].n++;
        }
    }
    sort(l+1,l+n+1,cmp);
    sort(k+1,k+m+1,cmp);
    sort(l+1,l+q+1,cmp1);
    sort(k+1,k+p+1,cmp1);
    for(int i=1;i<=p;i++) cout<<k[i].p<<" ";
    cout<<endl;
    for(int i=1;i<=q;i++) cout<<l[i].p<<" ";
    return 0;
}

sort(l+1,l+n+1,cmp);是怎末执行的不懂