Data Structures and Agorithm: DS 04 Linked List.pptx

1. Data Structure
Lecture No. 4
Linked List
Engr. Rashid Farid Chishti
http://youtube.com/rfchishti
http://sites.google.com/site/chishti
International Islamic University H-10, Islamabad, Pakistan
Video Lecture

2. Linked List
head
2 6 8 7
current
1 NULL
0x100 6
0x108
2
0x10C
0x110
0x114 7
0x118
0x11C 8
0x120
1
0x124
0x128 0x000
0x12C 0x11C
0x130
head
current
2
6
8 7 1
0x10C
0x100
0x11C
0x114
0x100

3. push_front (int Data){
node *newNode ;
// add new node
newNode = new node ;
newNode -> data = Data ;
newNode -> next = head ;
head = newNode ;
}
Linked List Operations
head
2 6 1 NULL
head
NULL
NULL 9
newNode
newNode
9
Data = 9

4. void push_back ( int Data ){
node *current, *newNode ;
// list is empty then create first node
if ( head == NULL ){
head = new node ;
head -> data = Data ;
head -> next = NULL ;
}
else{ // go to last node
current = head ;
while ( current -> next != NULL )
current = current -> next ;
newNode = new node ;
newNode -> data = Data ;
newNode -> next = NULL ;
current -> next = newNode ;
}
}
Linked List Operations
head
current
2 6 1 NULL
head
newNode
NULL
NULL
9
9
NULL
Data = 9

5. void addafter(int loc, int Data){
node *current = head, *newNode ;
// skip to desired portion
for ( int i = 0 ; i < loc ; i++ ){
current = current -> next ;
// if reached at end of linked list
if ( current == NULL ){
cout << "nThere are less than "
<< loc << " elements in list"
<< endl ;
return ;
}
}
newNode = new node ; // insert new node
newNode -> data = Data ;
newNode -> next = current -> next ;
current -> next = newNode ;
}
Linked List Operations
current
2 6 1 NULL
head
9
newNode
i = 0
1
loc = 1 Data = 9

6. void del ( int Data ) {
node *previous, *current ;
current = head ;
while ( current != NULL ){
if ( current -> data == Data ){
if ( current == head )
head = current -> next ;
else
previous->next = current->next;
delete current ;
return ;
}
else{
previous = current ;
current = current -> next ;
}
}
cout << "nnElement " << Data << " not found" ;
}
Linked List Operations
head
NULL
1
current
previous
Data = 1

7. void del ( int Data ) {
node *previous, *current ;
current = head ;
while ( current != NULL ){
if ( current -> data == Data ){
if ( current == head )
head = current -> next ;
else
previous->next = current->next;
delete current ;
return ;
}
else{
previous = current ;
current = current -> next ;
}
}
cout << "nnElement " << Data << " not found" ;
}
Linked List Operations
current
2 6
head
9 NULL
1
previous
previous
Data = 1

8. #include <iostream>
using namespace std;
class Linked_List{
private :
struct node{
int data ;
node * next ;
} *head ;
public :
Linked_List ( ) ;
void push_back ( int Data ) ;
void push_front ( int Data ) ;
void addafter ( int loc, int Data ) ;
void display ( ) ;
int count ( ) ;
void del ( int num ) ;
~Linked_List( ) ;
} ;
8
Example 1: Linked List
Linked_List :: Linked_List( ){
head = NULL ;
}
// adds node at the end of linked list
void Linked_List :: push_back ( int Data ){
node *current, *newNode ;
// list is empty then create first node
if ( head == NULL ){
head = new node ;
head -> data = Data ;
head -> next = NULL ;
}
else{ // go to last node
current = head ;
while ( current -> next != NULL )
current = current -> next ;
// add node at the end
1 2

9. newNode = new node ;
newNode -> data = Data ;
newNode -> next = NULL ;
current -> next = newNode ;
}
}
// adds a node at the beginning
void Linked_List :: push_front (int Data){
node *newNode ;
// add new node
newNode = new node ;
newNode -> data = Data ;
newNode -> next = head ;
head = newNode ;
}
// adds node after numbers of nodes
void Linked_List::addafter(int loc,
int num){
9
Example 1: Linked List
node *current, *newNode ;
current = head ;
// skip to desired portion
for ( int i = 0 ; i < loc ; i++ ){
current = current -> next ;
// if reached at end of linked list
if ( current == NULL ){
cout << "nThere are less than "
<< loc << " elements in list"
<< endl ;
return ;
}
}
newNode = new node ; // insert new node
newNode -> data = num ;
newNode -> next = current -> next ;
current -> next = newNode ;
}
3 4

10. // displays the contents of the link list
void Linked_List :: display( ){
node *current = head ;
cout << endl ;
// traverse the entire linked list
while ( current != NULL ){
cout << current -> data << " " ;
current = current -> next ;
}
}
// counts the number of nodes present
int Linked_List :: count( ){
node *current = head ; int c = 0 ;
// traverse the entire linked list
while ( current != NULL ){
current = current -> next ;
c++ ;
}
return c ; }
10
Example 1: Linked List
// deletes the specified node
void Linked_List :: del ( int Data ) {
node *previous, *current ;
current = head ;
while ( current != NULL ){
if ( current -> data == Data ){
// if node to be deleted is the
// first node in the linked list
if ( current == head )
head = current -> next ;
else
previous->next = current->next;
// free memory occupied by node
delete current ;
return ;
}
// traverse the linked list till
// the last node is reached
5 6

11. else{
previous = current ;
// go to the next node
current = current -> next ;
}
}
cout << "nnElement " << Data
<< " not found" ;
}
// deallocates memory
Linked_List :: ~Linked_List( ){
while ( head != NULL ){
node *current = head;
head = head -> next ;
delete current ;
}
}
11
Example 1: Linked List
int main( ) {
Linked_List l ;
l.push_back (14) ; l.push_back (30) ;
l.push_back (25) ; l.push_back (42) ;
l.push_back (17) ;
cout <<"nData in the linked list: ";
l.display( ) ;
l.push_front (999) ; l.push_front (888) ;
l.push_front (777) ;
cout << "nnData in the linked list "
" after addition at the "
" beginning: " ;
l.display( ) ;
l.addafter (7, 0); l.addafter (2,1);
l.addafter (5,99);
cout << "nnData in the linked list"
" after addition at given"
" position: " ;
7 8

12. l.display( ) ;
cout <<"nNo. of elements in the "
" linked list " << l.count( );
l.del (99) ;
l.del ( 1) ;
l.del (10) ;
cout << "nnData in the linked list"
" after deletion: " ;
l.display( ) ;
cout <<"nNo. of elements in the"
" linked list: " << l.count();
system("PAUSE");
return 0;
}
12
Example 1: Linked List
9 10

13. Example 1: Linked List

14.  push_front()
 we simply insert the new node after the current node. So add is a one-step operation.
 push_back()
 we have to traverse the entire list to insert the new node at the end of Linked List.
 del()
 We first search the node to be deleted.
 worst-case: may have to search the entire list
 Moving forward in a singly-linked list is easy but moving backwards is not so
easy.
 Moving backwards requires traversing the list from the start until the node
whose next pointer points to current node.
Analysis of Linked List

15.  Dynamic memory allocation : We use linked list of free blocks.
 Implementation of stacks and queues
 Maintaining directory of names.
 Performing arithmetic operations on long integers
 Addition and Multiplication of Polynomials.
 Implementation of Graphs. (Adjacency list representation of Graph).
 Representing sparse matrices.
 For separate chaining in Hashtables.
 Undo functionality in Photoshop or Word . Linked list of states.
 Graph Plotting Application.
Applications of Linked List

16.  In single linked list, every node points to its next node in the sequence and the
last node points to NULL.
 But in circular linked list, every node points to its next node in the sequence
but the last node points to the first node in the list.
Circular Linked List

17.  The real life application where the circular linked list is used is our Personal
Computers, where multiple applications are running. All the running
applications are kept in a circular linked list and the OS gives a fixed time slot
to all for running. The Operating System keeps on iterating over the linked list
until all the applications are completed.
 Another example can be Multiplayer games. All the Players are kept in a
Circular Linked List and the pointer keeps on moving forward as a player's
chance ends.
 Circular Linked List can also be used to create Circular Queue. In a Queue we
have to keep two pointers, FRONT and REAR in memory all the time, where as
in Circular Linked List, only one pointer is required.
Applications of Circular Linked List