Class 49: Linked Lists

Held: Monday, 28 November 2005

Summary: Today we consider another implementation of the list ADT, one based on linked nodes.

Related Pages:

• EBoard.
• Sample Code.

Overview:

• The design of lists, revisited.
• A vector-based implementation.
• A linked implementation.
• Doubly-linked lists.
• Circularly-linked lists.

Review

• Lists are dynamic, homogeneous collections in which the primary operation is iteration, visiting each value in turn.
• We use cursors to step through the values. Using multiple cursors permits us to iterate more than once at a time.
• There are three ways to control the order of iteration:
  • In Simple Lists, the order is determined by the implementer of the list.
  • In Sequenced Lists, the order is determined by the client.
  • In Sorted Lists, the order is determined by an external comparator.

A Vector-Based Implementation

• The simplest implementation uses vectors to store the elements.
• Each cursor contains an integer that represents the position in the Vector.

A Linked Implementation

• A more dynamic implementation involves linking nodes together.
  • We call such implementations linked lists.
• As in the case of the linked queue, we keep track of the front and back of the list.
• Each cursor contains a reference to a node.

Doubly-Linked Lists

• Unfortunately, the remove operation is difficult in linked lists.
• One solution is to have bi-directional links.

Circularly-Linked Lists

• As you may have noted, the code for Sequenced Lists is likely to be filled with special cases.
• One technique, that we will not cover in depth, is to have a designated special node with a forward link to the front of the list and a backward link to the rear of the list. This node can never be deleted.