Doubly Linked List

A fast, amortised O(log n) doubly linked list implementation.

A doubly linked list is a type of linked list in which each node contains three elements: a data value, a pointer to the next node in the list, and a pointer to the previous node. This two-way linkage allows traversal of the list in both directions, forward and backward, which is a significant advantage over a singly linked list that can only be traversed in one direction.

Installation

The package can be installed by adding doubly_linked_list to your list of dependencies in mix.exs:

def deps do
  [
    {:doubly_linked_list, "~> 0.1.0"}
  ]
end

Usage (full documentation)

A new doubly linked list can be constructed using new/0:

iex> dll = DoublyLinkedList.new()
#DoublyLinkedList<[]>

Many types of insertion and deletion are supported, the most basic being insert_head/2, insert_tail/2, remove_head/1 and remove_tail/2 which will insert and remove at the head and tail of the doubly linked list respectively:

iex> dll = DoublyLinkedList.new()
#DoublyLinkedList<[]>

iex> {dll, node} = DoublyLinkedList.insert_tail(dll, "tail value")
{#DoublyLinkedList<["tail value"]>, #DoublyLinkedNode<"tail value">}

iex> {dll, node} = DoublyLinkedList.insert_head(dll, "head value")
{#DoublyLinkedList<["head value", "tail value"]>, #DoublyLinkedNode<"head value">}

iex> dll = DoublyLinkedList.remove_tail(dll)
#DoublyLinkedList<["head value"]>

iex> dll = DoublyLinkedList.remove_head(dll)
#DoublyLinkedList<[]>

Node data can be updated with update/3:

iex> dll = DoublyLinkedList.new()
#DoublyLinkedList<[]>

iex> {dll, node} = DoublyLinkedList.insert_tail(dll, "tail value")
{#DoublyLinkedList<["tail value"]>, #DoublyLinkedNode<"tail value">}

iex> dll = DoublyLinkedList.update(dll, node, "new tail value")
#DoublyLinkedList<["new tail value"]>

There are two options for traversal. DoublyLinkedList implements the Enumerable protocol so Enum.map/2, Enum.member?/2, etc are supported; there are also the built-in find_from_head/2 and find_from_tail/2 functions. find_from_tail/2 is of particular interest as it traverses the list in reverse. Note that traversal methods are O(n).

iex> dll = DoublyLinkedList.new()
iex> {dll, node} = DoublyLinkedList.insert_tail(dll, 1)
iex> {dll, node} = DoublyLinkedList.insert_tail(dll, 2)
{#DoublyLinkedList<[1, 2]>, #DoublyLinkedNode<2>}

iex> Enum.map(dll, fn v -> v * 2 end)
[2, 4]

License

DoublyLinkedList is released under the Apache License 2.0.

About

This package was written by Elliot Jackson.

• Blog: https://elliotekj.com
• Email: elliot@elliotekj.com