Linked Lists Based on D.S. Malik, Java Programming: Program Design Including Data Structures
Nov 07, 2014
Linked Lists
Based on D.S. Malik, Java Programming: Program Design Including Data Structures
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Linked Lists Linked list
List of items, called nodes The order of the nodes is determined by the address,
called the link, stored in each node Every node (except the last node) contains the
address of the next node Components of a node
data/info: stores the relevant information link: stores the address of the next node
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Linked Lists head or first
Holds the address of the first node in the list The info part on the node can be either a value of a
primitive type or a reference to an object Class Node
Represents nodes on a list It has two instance variables
info (of type int, but it can be any other type) link (of type Node)
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Linked Lists
Class Nodepublic class Node{ public int info; public Node link;}
Notice that instance variables of the class Node are declared as public
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Linked List: Some Properties
Consider the following linked list
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Linked List: Some Properties Now consider the statement
current = head;
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Linked List: Some Properties Now consider the statement
current = current.link;
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Linked List: Some Properties
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Traversing a Linked List
Basic operations of a linked list that require the link to be traversed Search the list for an item Insert an item in the list Delete an item from the list
You cannot use head to traverse the list Why? You would lose the nodes of the list. Use another reference variable of the same type as head: current
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Traversing a Linked List The following code traverses the listcurrent = head;while (current != null){ //Do something - process current current = current.link;}
Example: The following code outputs the data /in each node
current = head;while (current != null){ System.out.println(current.info + “ “); current = current.link;}
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Item Insertion and Deletion
Consider the following definition of a nodepublic class Node { public int info; public Node link;}
And the following variable declarationNode head, p, q, newNode;
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Insertion Consider the following linked list
We want to create a new node with info 50 and insert it after p
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Insertion The following statements create and store 50 in the info field of a new node
newNode = new Node(); //create newNode
newNode.info = 50; //store 50 in the new node
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Insertion (continued) The following statements insert the node in the
linked list at the required placenewNode.link = p.link;
p.link = newNode;
The sequence of statements to insert the node is very important If you reverse the sequence of the statements, you
will not get the desired result
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Insertion
List after the statement newNode.link = p.link; executes
List after the statement p.link = newNode; executes
newNode.link = p.link;p.link = newNode;
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Insertion
Using two reference variables, we can simplify the code somewhat
Consider the following
List with reference variables p and q
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Insertion
The following statements insert newNode between p and qnewNode.link = q;
p.link = newNode;
orp.link = newNode;
newNode.link = q;
The order in which these statements execute does not matter
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Insertion
List after the statement newNode.link = q; executes
List after the statement p.link = newNode; executes
p.link = newNode;newNode.link = q;
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Deletion
Consider the following linked list
We want to delete node with info 34
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Deletion
The following statement removes the node from the list p.link = p.link.link
List after the statement p.link = p.link.link; executes
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Deletion
Previous statement removed the node However, the memory may still be occupied by this
node System’s automatic garbage collector reclaims
memory occupied by unreferenced nodes Could use System.gc(); to manually run the
garbage collector
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Deletion
Using two reference variables, you can simplify the code somewhat
Consider the following statementsq = p.link;
p.link = q.link;
q = null;
System.gc();
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Deletion (continued)
List after the statement p.link = q.link; executes
List after the statement q = p.link; executes
q = p.link;p.link = q.link;
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Building a Linked List You can build a list in two ways: forward or
backward Forward manner
A new node is always inserted at the end of the linked list
Backward manner A new node is always inserted at the beginning of the
linked list
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Building a Linked List Forward
A new node is always inserted at the end of the linked list
You need three reference variables One to point to the front of the list
Cannot be moved without destroying the list One to point to the last node of the list One to create the new node
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Building a Linked List ForwardNode buildListForward(){
Node first, newNode, last;
int num;
System.out.println(“Enter integers (999 to stop):”);
num = input.nextInt(); //priming read
first = null;
while (num != 999) {
newNode = new Node();
newNode.info = num;
newNode.link = null;
if (first == null) { //empty list
first = newNode;
last = newNode;
}
else {
last.link = newNode;
last = newNode;
}
num = input.nextInt(); //next read
}
return first;
}
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Building a Linked List Backward A new node is always inserted at the beginning of
the linked list You only need two reference variables
One to point to the front of the list Changes each time a new node is inserted
One to create the new node
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Building a Linked List BackwardNode buildListBackward(){
Node first, newNode;
int num;
System.out.println (“Enter integers (999 to stop):”);
num = input.nextInt(); //priming read
first = null;
while (num != 999) {
newNode = new Node(); //create a node
newNode.info = num; //store the data in newNode
newNode.link = first; //put newNode at the beginning
first = newNode; //update the head of the list
num = input.nextInt();//next read
}
return first;
}
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Linked List as an ADT
UML class diagram of the interface LinkedListADT
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Linked List as an ADT There are two types of linked lists: sorted (ordered)
and unsorted (unordered) The algorithms to implement some of the operations
differ for sorted and unsorted lists Therefore, define the LinkedListClass as an
abstract class LinkedListClass has two derived classes
UnorderedLinkedList OrderedLinkedList
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Structure of Linked List Nodes
Each node of a linked list must keep track of the data as well as the next node in the list
The node has two instance variables The class LinkedListNode is defined as an inner
class of LinkedListClass Simplify operations such as insert and delete
LinkedListNode is defined as protected and generic
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Structure of Linked List Nodes
UML class diagram of the class LinkedListNode and the outer-inner class relationship
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Instance Variables of the Class LinkedListClass
Instance variables
protected LinkedListNode<T> first;
//variable to store the address of the first node
protected LinkedListNode<T> last;
//variable to store the address of the last node
protected int count;
//variable to store the number of nodes in the list
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Linked List Iterators
UML class diagram of the class LinkedListIterator and the outer-inner class relationship
NOTE: An iterator is an object that produces each element of a collection one element at a time
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class LinkedListClass
UML class diagram of the class LinkedListClass
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class LinkedListClass
Definition of the class LinkedListClass
public abstract class LinkedListClass<T> implements LinkedListADT<T> {
//Place the definition of the class LinkedListNode<T> here.
//Place the definition of the class LinkedListIterator<T> here.
//Place instance variables here
//Place the definition of the nonabstract methods here
//Place the definition of the abstract methods here.
}
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Unordered Linked List
UML class diagram of the class UnorderedLinkedList and the inheritance hierarchy
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Ordered Linked Lists
UML class diagram of the class OrderedLinkedList and the inheritance hierarchy
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Double Linked Lists Linked list in which every node has a next pointer
and a back pointer A double linked list can be traversed in either
direction
public class DoubleLinkedListNode<T> implements Cloneable{ T info; DoubleLinkedListNode<T> next; DoubleLinkedListNode<T> back; ...}
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Circular Linked Lists A linked list in which the last node points to the first
node It is convenient to make first point to the last
node
Circular linked list with more than one node