Doubly linked lists-implementation, Data Structure & Algorithms

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In any singly linked list, each of the elements contains a pointer to the next element. We have illustrated this before. In single linked list, traversing is probable only in one direction. Sometimes, we ought to traverse the list in both of the directions to improve performance of algorithms. To enable this, we require links in both the directions, i.e., the element has to have pointers to the right element in addition toto its left element. This type of list is called  asdoubly linked list.

141_DOUBLY LINKED LISTS-IMPLEMENTATION.png

Figure: A Doubly Linked List

Doubly linked list is described as a collection of elements, each of element consisting of three fields:

Ø  pointer to left element,

Ø  data field, &

Ø  pointer to right element.

Left link of the leftmost element is set to NULL that means that there is no left element to that. And, right link of the rightmost element is set to NULL that means that there is no right element to that.

ALGORITHM  (Creation)

Step 1                begin

Step 2                define a structure ELEMENT with  fields

Data

Left pointer

Right pointer

Step 3                declare any pointer by name head and using (malloc()) memory allocation  function  allocate  space  for  one  element  &  store  the address in head pointer

Head = (ELEMENT *) malloc(sizeof(ELEMENT))

Step 4                read the value for head->data head->left = NULL

head->right = (ELEMENT *) malloc(size of (ELEMENT))

Step 5                repeat step3 to create needed number of elements

Step 6                end

 

Program demonstrated the creation of a Doubly linked list.

/* CREATION OF A DOUBLY LINKED LIST */

/* DBLINK.C */

# include

# include

structdl_list

{

int data;

structdl_list *right;

structdl_list *left;

};

typedefstructdl_listdlist;

voiddl_create (dlist *);

void traverse (dlist *);

/* Function creates simple doubly linked list */

voiddl_create(dlist *start)

{

printf("\n Insert values of element -1111 to come out : ");

scanf("%d", &start->data);

if(start->data != -1111)

{

start->right = (dlist *) malloc(sizeof(dlist));

start->right->left = start;

start->right->right = NULL;

dl_create(start->right);

}

else

start->right = NULL;

}

/* Display the list */

void traverse (dlist *start)

{

printf("\n traversethe list usingright pointer\n");

do {

printf(" %d = ", start->data);

start = start->right;

}

while (start->right); /* Demonstrates value of last start only one time */

printf("\n traversethe listusing left pointer\n");

start=start->left;

do

{

printf(" %d =", start->data);

start = start->left;

}

while(start->right);

}

{

dlist *head;

head = (dlist *) malloc(sizeof(dlist));

head->left=NULL; head->right=NULL; dl_create(head);

printf("\n created doubly linked list is as ");

traverse(head);

}


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