Introduction
In Computer Science, one of the most basic and fundamental data structures is the linked list, which functions similarly to an array. The principal benefit of a linked list over a conventional array is that the list elements can easily be inserted or removed without reallocation of any other elements.
In some programming languages, the size of an array is a concern and one of the ways to overcome that problem and allow dynamically allocated data is using linked lists.
Luckily in Ruby, arrays aren’t limited to a certain size, and both insertion and deletion can be done trivially at any index using the appropriate built in array method, so you don’t have to think about overcoming those limitations.
So if array size, array insertion and array deletion are not limitations in Ruby, are linked lists really necessary? The short answer to that is no; however, it’s the simplest of the dynamic data structures and it will give you a solid foundation, so you can understand more complex data structures like graphs and binary trees with more ease.
Structure of a linked list
A linked list is a linear collection of data elements called nodes that “point” to the next node by means of a pointer.
Each node holds a single element of data and a link or pointer to the next node in the list.
A head node is the first node in the list, a tail node is the last node in the list. Below is a basic representation of a linked list:
[ NODE(head) ] -> [ NODE ] -> [ NODE(tail) ] -> nil
For a more thorough explanation, use these resources:
Assignment
You will need two classes:
LinkedList
class, which will represent the full list.Node
class, containing a#value
method and a link to the#next_node
, set both asnil
by default.
Build the following methods in your linked list class:
#append(value)
adds a new node containingvalue
to the end of the list#prepend(value)
adds a new node containingvalue
to the start of the list#size
returns the total number of nodes in the list#head
returns the first node in the list#tail
returns the last node in the list#at(index)
returns the node at the givenindex
#pop
removes the last element from the list#contains?(value)
returns true if the passed in value is in the list and otherwise returns false.#find(value)
returns the index of the node containing value, or nil if not found.#to_s
represent your LinkedList objects as strings, so you can print them out and preview them in the console. The format should be:( value ) -> ( value ) -> ( value ) -> nil
Extra credit
#insert_at(value, index)
that inserts a new node with the providedvalue
at the givenindex
.#remove_at(index)
that removes the node at the givenindex
.
Extra Credit Tip: When you insert or remove a node, consider how it will affect the existing nodes. Some of the nodes will need their #next_node
link updated.