CIS3023: Programming Fundamentals for CIS Majors IISummer 2010

Ganesh Viswanathan

Linked Lists

Course Lecture Slides 23 July 2010

“A list is only as strong as its weakest link.” --Donald Knuth

Data structure

• A way of structuring, storing and organizing data in computers that facilitates efficient operations on the data.

• Data structures help to devise algorithms for solving complex operations on the data in an efficient manner.

Data structures

Stack

Queue

Tree

And many more!

ArrayListTo insert (remove) an element in (from) the

interior of an ArrayList requires shifting of data and is a linear-time O(n) operation!

Linked List

• Is a collection of linked nodes (think of a chain!)

• Memory allocation for nodes is non-contiguous

• Sports constant time O(1) insertion and updates

Linked List Variations• Singly-Linked Lists• Doubly-Linked Lists• Multi-Linked Lists• Circular Linked Lists• Unrolled Linked Lists (multiple elements in each node)

• Lists with only head pointer nodes• With head and tail nodes• With head, tail and cursor (currently requested)

nodesAnd many more!

Singly Linked List

A set of nodes, each containing some data and a link to the next node.

Dynamic data-structure.

Singly Linked List

A set of nodes, each containing some data and a link to the next node.

Dynamic data-structure.

Advantages: • Simple implementation, • Efficient, constant time O(1) insertion and

removal operation.

Singly Linked List

Node : self-referencing structure Link : reference to a nodeLinked list: List of nodes

Has dedicated head and tail indicators

Operations on Singly Linked List

• Create list• Add node

• Add node at head• Add node at tail• Add node at index i

• Remove node• Remove node at head• Remove node at tail• Remove node at index i

• Iterate (traverse) the list• Find node at index

• Find previous node to the one at index i

• Set node at index ito new node

• Size of list• Clear list

Create (Node)public class Node<T>

{// data held by the node

public T nodeValue;// next node in the list

public Node<T> next;

// default constructor with no initial value

public Node(){

nodeValue = null;

next = null;}...

}

Empty List

If list is empty (head == null) Set both head and tail to point to new node

Singly Linked List: Add node

Add node to head

Insert new node before current head nodeTwo-step process

Singly Linked List: Add node

Add node to head

1. Update the next link of a new node, to point to the current head node.

Singly Linked List: Add node

2. Update head link to point to the new node.

Add node to tail

Insert new node after current tail nodeTwo-step process

Singly Linked List: Add node

Add node to head

1. Update the next link of the current tail node, to point to the new node.

Singly Linked List: Add node

2. Update tail link to point to the new node.

Add node at index i

If node at index i represents head or tail node, Refer previous pseudo-code for “add node at head/ tail”

Else Two-step process

Singly Linked List: Add node

Add node at index i

1. Update link of the new node, to point to the "next" node.

Singly Linked List: Add node

2. Update link of the "previous" node, to point to the new node.

Remove node from list with only one node

Both head and tail point to the (same node) only existing node.• Remove link to the node from both the head and tail,

by setting both to null.• Dispose off the node (set to null)

Singly Linked List: Remove node

Remove node from head

• Remove the node pointed to by head.• Two-step process

Singly Linked List: Remove node

Remove node from head

Singly Linked List: Remove node

1. Update head link to point to the node, next to the head.

2. Dispose removed node.

Remove node from tail

• Remove the node pointed to by tail. • Need access to the previous node of current tail.• Three-step process

Singly Linked List: Remove node

Remove node from tail

Singly Linked List: Remove node

1. Update tail link to point to the node, before the tail. In order to find it, list should be traversed first, beginning from the head.

2. Set next link of the new tail to NULL. 3. Dispose removed node.

Remove node at index i

• If index i is not 0 or n-1, this operation removes the node between two nodes.

• Two-step process

Singly Linked List: Remove node

Remove node at index i

Singly Linked List: Remove node

1. Update next link of the previous node, to point to the next node, relative to the removed node.

2. Dispose removed node.

Doubly Linked List

• Has links to both previous and next nodes• Advantage: faster (bi-directional) traversal• But, more control data (links) stored

Get more info!• Java docs: Linked List (doubly linked list)

• Java docs: Using and programming generics in J2SE 5.0

• Java docs: Collections framework tutorial

http://download.oracle.com/docs/cd/E17476_01/javase/1.5.0/docs/api/java/util/LinkedList.html

http://java.sun.com/developer/technicalArticles/J2SE/generics/

http://download.oracle.com/docs/cd/E17409_01/javase/tutorial/collections/index.html