sorting a doubly linked list with merge sort

Question

I have found this code in the internet and it was for arrays ,I want to change it for doubly linked list(instead of index we should use pointer) would you please help me tha

Answer 1

First of all, you must NOT use indexes when dealing with linked lists. Do it like this:

while (i < in.size/2){
  listOne.addLast( in.remove(in.first()) );
  i++
}
while(!in.isEmptly){
  listTwo.addLast( in.remove(in.first()) );
}

And for merging

merge(a, b, out){
  while(!a.empty && !b.empty){
    if(a.first() >= b.first())
      out.addLast( a.remove(a.first()) );
    else
     out.addLast( b.remove(b.first()) );

  //remember to take care of the remaining elements 
  while(!a.empty)
    out.addLast( a.remove(a.first()) );
  while(!b.empty)
    out.addLast( b.remove(b.first()) );
}

This way it will still be O(n log n)