Download Linked Lists

CIS3023: Programming Fundamentals for CIS Majors II
Summer 2010
Linked Lists
“A list is only as strong as its weakest link.” --Donald Knuth
Course Lecture Slides
23 July 2010
Ganesh Viswanathan
[News] Tropical storm Bonnie hit Biscayne Bay, FL this morning!
Credits: NOAA
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!
ArrayList
To 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)
nodes
And 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 node
Linked 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 i
to new node
• Size of list
• Clear list
public class Node<T>
{
Create (Node)
// 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;
}
...
}
Singly Linked List: Add node
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 node
Two-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.
2. Update head link to point
to the new node.
Singly Linked List: Add node
Add node to tail
Insert new node after current tail node
Two-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.
2. Update tail link to point
to the new node.
Singly Linked List: Add 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.
2. Update link of the
"previous" node, to point to
the new node.
Singly Linked List: Remove 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
1. Update head link to point to
the node, next to the head.
2. Dispose removed node.
Singly Linked List: Remove 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
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.
Singly Linked List: Remove 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
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)
http://download.oracle.com/docs/cd/E17476_01/javase/1.5.0/docs/api/
java/util/LinkedList.html
• Java docs: Using and programming generics in
J2SE 5.0
http://java.sun.com/developer/technicalArticles/J2SE/generics/
• Java docs: Collections framework tutorial
http://download.oracle.com/docs/cd/E17409_01/javase/tutorial/col
lections/index.html