uni/ws2019/ipi/uebungen/cpp_headers/Mergesort.cc

template <class C> 
void rec_merge_sort (C& a, int o, int n) 
{   // sortiere Eintraege [o,o+n-1]
  if (n==1) return;
    
  // teile und sortiere rekursiv
  int n1=n/2;
  int n2=n-n1;
  rec_merge_sort(a,o,n1);
  rec_merge_sort(a,o+n1,n2);

  // zusammenfuegen
  C b(n); // Hilfsfeld
  int i1=o, i2=o+n1;
  for (int k=0; k<n; k=k+1)
    if ((i2>=o+n) || (i1<o+n1 && a[i1]<=a[i2]))
      b[k] = a[i1++];
    else
      b[k] = a[i2++]; 

  // umkopieren
  for (int k=0; k<n; k=k+1) a[o+k] = b[k];
}

template <class C> 
void mergesort (C& a) 
{
  rec_merge_sort(a,0,a.size());
}