Variations on the list

• It can be useful to have "housekeeping" information in the the list class:

  private: int length; Node *head, *last;

• One can use an entire dummy node as the head, rather than simply a pointer:

  private: Node head;

  This can eliminate some special cases in the insert/delete code.

• The list type we have defined uses "internal" data for its nodes. Often one defines "external" data instead:

  class ListNode { Item * element; // store only a pointer ListNode * next; };

Doubly linked lists

One other important variation on linked lists is to have list nodes point both to the next and the previous element. Among other things, this makes it easy to traverse a list backwards:

struct ListNode { int value; ListNode * next, *prev; }; class LinkedList { // some stuff, then: private: ListNode * head, * last; }; // Reverse traversal void List::printReverseOrder() { ListNode * current = last; while (current != NULL) { cout << current->value << endl; current = current->prev; } }