CS 350 : Data Structures Linked Listsfaculty.ycp.edu/~dbabcock/PastCourses/cs350/lectures/Linked_Lists.pdf · - circular linked lists ... CS 350: Data Structures Linked List Insertion

CS 350: Data Structures © James Moscola

College Catalog2009–2011

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David Babcock (courtesy of James Moscola)Department of Physical SciencesYork College of Pennsylvania

CS 350 : Data StructuresLinked Lists

Department of Physical SciencesYork College of Pennsylvania

Monday, September 3, 12

CS 350: Data Structures

Linked Lists

• Come in a variety of different forms- singly linked lists- doubly linked lists- circular linked lists

• Composed of a set of nodes that hold data and contain one or more pointers to neighboring nodes in the list- singly linked lists contain only a pointer to the next node in the list- doubly linked lists contain a pointer to the next node and the

previous node in the list

2

data



Linked List Operations

• Basic operations include:-insert / add

-remove

• Additional operations may include:-getFirst

-getLast

-find

-isEmpty

-makeEmpty

3Monday, September 3, 12


Linked List Insertion

• Basic implementation uses a head pointer that points to the first node in the list- Points to null upon initialization when no nodes exist in the list

• Depending on implementation, insertion may take place at the head of the list, at the tail of the list, or at some other specified node

4

head

null




5

Start with Empty List

head points to the front of the linked list

tail points to the back of the linked list

head

null

tail



null


6

head

tail



null


6

head

Insert Value: A

nullA

tail



null


7

head

nullA

tail



null


7

head

Insert Value: B

nullA

tail

nullB



null


8

head

nullA

tail

nullB



null


8

head

Insert Value: C

nullA

tail

nullB nullC



null

Linked List Removal

9

head

nullA

tail

nullB nullC



null

Linked List Removal

9

head

Remove First Value:

nullA

tail

nullB nullC



Linked List Removal

• Removing last value is not very efficient when using singly linked lists- Want to make next-to-last node in list the last node- Must traverse entire list, starting from the head, to find the next-to-

last node in the list- O(N)

10

null

head

nullA

tail

nullB nullC



Linked List Implementation

11

public class LinkedListNode<E> { public E data; public LinkedListNode<E> next; }




12

// Inserts at the tail of the list

public void insert (E data) { LinkedListNode<E> newNode = new LinkedListNode<E>(); newNode.data = data; // assign data to newNode tail.next = newNode; tail = newNode; }




12

// Inserts at the tail of the list


This method is oversimplified, what happensif this is called when the list is empty?




13

// Inserts at the tail of the list public void insert (E data) { LinkedListNode<E> newNode = new LinkedListNode<E>(); newNode.data = data; // assign data to newNode if (isEmpty()) { head = tail = newNode; } else { tail.next = newNode; tail = newNode; } }

Fixed insert method




14

// Inserts at the head of the list public void insertAtHead (E data) { LinkedListNode<E> newNode = new LinkedListNode<E>(); newNode.data = data; // assign data to newNode newNode.next = head; head = newNode; }




14


This method is oversimplified, what happensif this is called when the list is empty?




15

// Inserts at the head of the list public void insertAtHead (E data) { LinkedListNode<E> newNode = new LinkedListNode<E>(); newNode.data = data; // assign data to newNode newNode.next = head;

if (!isEmpty()) { head = newNode; } else { head = tail = newNode; } }




16

// Removes node from head of list and returns its value public E remove() { if (head != null) { E nodeData = head.data; head = head.next; return nodeData; } else { return null; } }



Considerations for Linked List Implementation

• Implementation as previously shown requires a error checking in the insert and remove methods to check for edge cases (i.e. checking for an empty list)

• To improve the speed of the Linked List operations, it is possible to remove these tests- Tradeoff: speedup comes at the expense of one additional ‘dummy’

node in the Linked List

• Idea: create a dummy node that exists in the linked list at ALL times ... it is created as part of the list and points to the head node- Eliminates the need to always check for null- Generalized the insert and remove methods

17Monday, September 3, 12


• Implementation as previously shown requires error checking in the insert and remove methods to check for edge cases (i.e. checking for an empty list)

null null null

Linked List with Header Node

18

head

nullA

tail

null null

head

tail

Empty list List with single node




19

// Inserts at the tail of the list // When using dummy header node, no need to test for null





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CS 350 : Data Structures Linked Listsfaculty.ycp.edu/~dbabcock/PastCourses/cs350/lectures/Linked_Lists.pdf · - circular linked lists ... CS 350: Data Structures Linked List Insertion

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