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Data Structures: Doubly Linked List (with C Program source code, tutorial and MCQ Quiz)




Some Important Linear Data Structures- at a glance

 

Doubly Linked Lists

Doubl

To go through the C program / source-code, scroll down this page

Doubly Linked List

Doubly-linked list is a more sophisticated form of linked list data structure. Each node of the list contain two references (or links) – one to the previous node and other to the next node. The previous link of the first node and the next link of the last node points to NULL. In comparison to singly-linked list, doubly-linked list requires handling of more pointers but less information is required as one can use the previous links to observe the preceding element. It has a dynamic size, which can be determined only at run time.

Related Tutorials :

 Single Linked List

 A self referential data structure. A list of elements, with a head and a tail; each element points to another of its own kind.

 Double Linked List

 A self referential data structure. A list of elements, with a head and a tail; each element points to another of its own kind in front of it, as well as another of its own kind, which happens to be behind it in the sequence. 

 Circular Linked List

 Linked list with no head and tail - elements point to each other in a circular fashion.


Performance

1. The advantage of a doubly linked list is that we don’t need to keep track of the previous node for traversal or no need of traversing the whole list for finding the previous node.
2. The disadvantage is that more pointers needs to be handled and more links need to updated.




Double Linked List - C Program source code



#include<stdio.h>
#include<stdlib.h>
typedef struct Node
{
        int data;
        struct Node *next;
        struct Node *prev;
}node;
void insert(node *pointer, int data)
{
        /* Iterate through the list till we encounter the last node.*/
        while(pointer->next!=NULL)
        {
                pointer = pointer -> next;
        }
        /* Allocate memory for the new node and put data in it.*/
        pointer->next = (node *)malloc(sizeof(node));
        (pointer->next)->prev = pointer;
        pointer = pointer->next;
        pointer->data = data;
        pointer->next = NULL;
}
int find(node *pointer, int key)
{
        pointer =  pointer -> next; //First node is dummy node.
        /* Iterate through the entire linked list and search for the key. */
        while(pointer!=NULL)
        {
                if(pointer->data == key) //key is found.
                {
                        return 1;
                }
                pointer = pointer -> next;//Search in the next node.
        }
        /*Key is not found */
        return 0;
}
void delete(node *pointer, int data)
{
        /* Go to the node for which the node next to it has to be deleted */
        while(pointer->next!=NULL && (pointer->next)->data != data)
        {
                pointer = pointer -> next;
        }
        if(pointer->next==NULL)
        {
                printf("Element %d is not present in the list\n",data);
                return;
        }
        /* Now pointer points to a node and the node next to it has to be removed */
        node *temp;
        temp = pointer -> next;
        /*temp points to the node which has to be removed*/
        pointer->next = temp->next;
        temp->prev =  pointer;
        /*We removed the node which is next to the pointer (which is also temp) */
        free(temp);
        /* Beacuse we deleted the node, we no longer require the memory used for it .
           free() will deallocate the memory.
         */

        return;
}
void print(node *pointer)
{
        if(pointer==NULL)
        {
                return;
        }
        printf("%d ",pointer->data);
        print(pointer->next);
}
int main()
{
        /* start always points to the first node of the linked list.
           temp is used to point to the last node of the linked list.*/

        node *start,*temp;
        start = (node *)malloc(sizeof(node));
        temp = start;
        temp -> next = NULL;
        temp -> prev = NULL;
        /* Here in this code, we take the first node as a dummy node.
           The first node does not contain data, but it used because to avoid handling special cases
           in insert and delete functions.
         */

        printf("1. Insert\n");
        printf("2. Delete\n");
        printf("3. Print\n");
        printf("4. Find\n");
        while(1)
        {
                int query;
                scanf("%d",&query);
                if(query==1)
                {
                        int data;
                        scanf("%d",&data);
                        insert(start,data);
                }
                else if(query==2)
                {
                        int data;
                        scanf("%d",&data);
                        delete(start,data);
                }
                else if(query==3)
                {
                        printf("The list is ");
                        print(start->next);
                        printf("\n");
                }
                else if(query==4)
                {
                        int data;
                        scanf("%d",&data);
                        int status = find(start,data);
                        if(status)
                        {
                                printf("Element Found\n");
                        }
                        else
                        {
                                printf("Element Not Found\n");

                        }
                }
        }


}

MCQ Quiz on Double Linked List

Companion MCQ Quiz for Double Linked Lists- test how much you know about the topic. Your score will be e-mailed to you at the address you provide.

MCQ Quiz: Double Linked Lists


Related Visualizations (Java Applet Visualizations for different kinds of Linked Lists) :



Lists : Linear data structures, contain elements, each of which point to the "next" in the sequence as demonstrated in the examples below ( Simple, Circular and Double Linked Lists are some common kinds of lists ) .  Additions and removals can be made at any point in the list - in this way it differs from stacks and queues. 


 

1. Simple Linked Lists - A Java Applet Visualization

2. Circular Linked Lists - A Java Applet Visualization

3. Double Linked Lists - A Java Applet Visualization




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