Data Structures and Agorithm: DS 05 Doubly Linked List.pptx

1. Data Structure
Lecture No. 5
Doubly 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.  Moving forward in a singly-linked list is easy; moving backwards is not so easy.
 To move back one node, we have to start at the head of the singly-linked list
and move forward until the node before the current.
 To avoid this we can use two pointers in a node: one to point to next node and
another to point to the previous node:
 Need to be more careful when adding or removing a node.
 Consider add: the order in which pointers are reorganized is important:
Doubly Linked List
next
prev data

3. current = current -> prev ;
dnode *temp = new dnode ;
temp -> data = num ;
temp -> prev = current ;
temp -> next = current -> next ;
temp -> next -> prev = temp ;
current -> next = temp ;
Adding a new Node
NULL
temp
head
next
prev 9
current
next
prev 6
NULL
next
prev 2 next
prev 1

4. Deleting a Node
next
prev 2
NULL next
prev 6
NULL
next
prev 2
next
prev 9
void linklist :: d_delete ( int num ){
dnode *current = head ;
while ( current != NULL ){
if ( current -> data == num ){
if ( current == head ){
head = head -> next ;
head -> prev = NULL ;
}
else{
if ( current -> next == NULL )
current -> prev -> next = NULL ;
else {
current -> prev -> next = current -> next ;
current -> next -> prev = current -> prev ;
}
delete current ;
}
return ;
}
current = current -> next ;
}
cout << num << " not found." ;
}
head
current
num = 9
If it is the first node
If it is the last node
If it is any intermediate node

5. #include <iostream>
using namespace std;
class linklist {
private :
struct dnode {
dnode *prev ;
int data ;
dnode * next ;
} *head ;
public :
linklist( ) ;
void d_append ( int num ) ;
void d_addatbeg ( int num ) ;
void d_addafter ( int loc, int num ) ;
void d_display( ) ;
int d_count( ) ;
void d_delete( int i ) ;
~linklist( ) ;
} ;
5
Example 1: Doubly Linked List
linklist :: linklist( ){
head = NULL ;
}
// adds a new node at the end
void linklist :: d_append ( int num ){
dnode *r, *current ;
current = head ;
// if the linked list is empty
if ( current == NULL ){
//create a new node
current = new dnode ;
current -> prev = NULL ;
current -> data = num ;
current -> next = NULL ;
head = current ;
}
1 2

6. else{
// traverse the linked list
while ( current -> next != NULL )
current = current -> next ;
// add a new node at the end
r = new dnode ;
r -> data = num ;
r -> next = NULL ;
r -> prev = current ;
current -> next = r ;
}
}
// adds a new node at the begining
void linklist :: d_addatbeg ( int num ){
dnode *newNode ;
// create a new node
newNode = new dnode ;
6
Example 1: Doubly Linked List
// assign data to the new node
newNode -> prev = NULL ;
newNode -> data = num ;
newNode -> next = head ;
// make new node the head node
head -> prev = newNode ;
head = newNode ;
}
// adds at a specified position
void linklist :: d_addafter ( int loc,
int num ){
dnode *current ;
current = head ;
// skip to desired portion
for ( int i = 0 ; i < loc ; i++ ){
current = current -> next ;
3 4

7. // if reached at end of list
if ( current == NULL ){
cout << "nThere are less than "
<< loc << " elements" ;
return ;
}
}
// insert new node
current = current -> prev ;
dnode *temp = new dnode ;
temp -> data = num ;
temp -> prev = current ;
temp -> next = current -> next ;
temp -> next -> prev = temp ;
current -> next = temp ;
}
7
Example 1: Doubly Linked List
// displays the the linked list
void linklist :: d_display( ){
dnode *temp = head ;
cout << endl ;
// traverse the entire linked list
while ( temp != NULL ){
cout << temp -> data << " " ;
temp = temp -> next ;
}
}
// counts the number of nodes
int linklist :: d_count( ){
int c = 0 ;
dnode *temp = head ;
// traverse the entire linked list
while ( temp != NULL ){
temp = temp -> next ; c++ ;
}
5 6

8. return c ;
}
// deletes the specified node
void linklist :: d_delete ( int num ){
dnode *current = head ;
// traverse the entire linked list
while ( current != NULL ){
// if node to be deleted is found
if ( current -> data == num ){
// if it is the first node
if ( current == head ){
head = head -> next ;
head -> prev = NULL ;
}
else{
// if it is the last node
if ( current -> next == NULL )
8
Example 1: Doubly Linked List
current -> prev -> next = NULL ;
else {
// if it is any intermediate node
current -> prev -> next =
current -> next ;
current -> next -> prev =
current -> prev ;
}
delete current ;
}
// return back after deletion
return ;
}
// go to next node
current = current -> next ;
}
cout << "n" << num << " not found." ;
}
7 8

9. // deallocates memory
linklist :: ~linklist( ){
while ( head != NULL ){
dnode *q = head;
head = head -> next ;
delete q ;
}
}
int main( ){
linklist l ;
l.d_append ( 11 ) ;
l.d_append ( 2 ) ;
l.d_append ( 14 ) ;
l.d_append ( 17 ) ;
l.d_append ( 99 ) ;
cout << "nElements in doubly linked list:
" ;
9
Example 1: Doubly Linked List
l.d_display( ) ;
cout << "nNo. of elements in the
" doubly linked list: " << l.d_count();
l.d_addatbeg ( 33 ) ;
l.d_addatbeg ( 55 ) ;
cout << "nnElements in doubly linked list
after addition at the beginning: " ;
l.d_display( ) ;
cout << "nNo. of elements in the doubly
linked list: " << l.d_count( ) ;
l.d_addafter ( 4, 66 ) ;
l.d_addafter ( 2, 96 ) ;
cout << "nnElements in doubly linked
list after addition at the given position: "
;
9 10

10. l.d_display( ) ;
cout << "nNo. of elements in the doubly
linked list: " << l.d_count( ) ;
l.d_delete ( 55 ) ;
l.d_delete ( 2 ) ;
l.d_delete ( 99 ) ;
cout << "nnElements in doubly linked
list after deletion: " ;
l.d_display( ) ;
cout << "nNo. of elements in the doubly
linked list: n" << l.d_count( )
<< endl;
system("PAUSE");
return 0;
}
10
Example 1: Doubly Linked List
11 12

11. Doubly Linked List

12.  Image viewer – Previous and next images are linked, hence can be accessed
by next and previous button.
 Previous and next page in web browser – We can access previous and next url
searched in web browser by pressing back and next button since, they are
linked as linked list.
 Music Player – Songs in music player are linked to previous and next song. you
can play songs either from starting or ending of the list.
Applications of Doubly Linked List