hybridsort senza randomized quicksort

#include <vector>
#include <iostream>
#include <cstdlib>
#include <ctime>
static const int M=10;

using namespace std;

void swap( int &A, int &B)
{
  	int t=A;
	A=B;
  	B=t;
}

void insertionsort (vector<int>&a, int l, int r)
  {
    int  key, i;
    for (int j=l+1; j <= r; j++)
    {
         key = a[j];
         i = j-1;
         while ( i >= l && a[i] > key)
         {
              a[i+1]= a[i];
              i--;
          }
          a[i+1]=key;
    }
}
void compswap ( int &A, int &B)
{
 	if (B >A) swap(A,B);
}
typedef int Item;
int partition(vector<int>&a, int l, int r)
{
 int i= l-1,  j=r;
 Item v = a.at(r);
 for(;;)
  {
   while(a.at(++i) < v);
   while(v< a.at(--j)) if (j == l) break;
   if (i >= j) break;
   swap(a.at(i),a.at(j));
  }
 swap(a.at(i),a.at(r));
 return i;
}

void quicksort(vector<int>&a, int l, int r)
{
    int c=r-l;
  	if (c > M)
	{
	    swap(a.at((l+r)/2),a.at(r-1));
  		compswap(a.at(l),a.at(r-1));
  		compswap(a.at(l),a.at(r));
  		compswap(a.at(r-1),a.at(r));
  		int i = partition(a,l+1,r-1);
  		quicksort(a,l,i-1);
  		quicksort(a,i+1,r);
	}
}

void hybridsort(vector<int>&a, int l, int r)
{
 	quicksort (a,l,r);
 	insertionsort (a,l,r);
}



int main()
{
    cout<<"Inserisci il numero di elementi da ordinare del vettore: ";
    int tot;
    cin>>tot;
    vector<int> arr1;
    int x;
    cout<<"Inserimento: "<<endl;
    for(int i=0; i < tot ; i++){
        cin>>x;
        arr1.push_back(x);
    }
    cout<<"\nQuickSort"<<endl;
    hybridsort(arr1,0,tot-1); //tot-1 = arr1.size()-1;
    for(auto z : arr1)
        cout<<"\n"<<z;
    return 0;
}