rev_doubly_linklist.c

/**
 * C program to reverse a Doubly linked list
 */

#include <stdio.h>
#include <stdlib.h>


/*
 * Basic structure of Node
 */
struct node {
    int data;
    struct node * prev;
    struct node * next;
}*head, *last;



/*
 * Functions used in this program
 */
void createList(int n);
void displayList();
void reverseList();


int main()
{
    int n, data, choice=1;

    head = NULL;
    last = NULL;

    /*
     * Runs forever until user chooses 0
     */
    while(choice != 0)
    {
        printf("============================================\n");
        printf("DOUBLY LINKED LIST PROGRAM\n");
        printf("============================================\n");
        printf("1. Create List\n");
        printf("2. Reverse List\n");
        printf("3. Display list\n");
        printf("0. Exit\n");
        printf("--------------------------------------------\n");
        printf("Enter your choice : ");

        scanf("%d", &choice);

        switch(choice)
        {
            case 1:
                printf("Enter the total number of nodes in list: ");
                scanf("%d", &n);
                createList(n);
                break;
            case 2:
                reverseList();
                break;
            case 3:
                displayList();
                break;
            case 0:
                break;
            default:
                printf("Error! Invalid choice. Please choose between 0-3");
        }

        printf("\n\n\n\n\n");
    }

    return 0;
}


/**
 * Creates a doubly linked list of n nodes.
 * @n Number of nodes to be created
 */
void createList(int n)
{
    int i, data;
    struct node *newNode;

    if(n >= 1)
    {
        /*
         * Create and link head node
         */
        head = (struct node *)malloc(sizeof(struct node));

        printf("Enter data of 1 node: ");
        scanf("%d", &data);

        head->data = data;
        head->prev = NULL;
        head->next = NULL;

        last = head;

        /*
         * Create and link rest of the n-1 nodes
         */
        for(i=2; i<=n; i++)
        {
            newNode = (struct node *)malloc(sizeof(struct node));

            printf("Enter data of %d node: ", i);
            scanf("%d", &data);

            newNode->data = data;
            newNode->prev = last; // Link new node with the previous node
            newNode->next = NULL;

            last->next = newNode; // Link previous node with the new node
            last = newNode; // Make new node as last/previous node
        }

        printf("\nDOUBLY LINKED LIST CREATED SUCCESSFULLY\n");
    }
}


/**
 * Display the content of the list from beginning to end
 */
void displayList()
{
    struct node * temp;
    int n = 1;

    if(head == NULL)
    {
        printf("List is empty.\n");
    }
    else
    {
        temp = head;
        printf("DATA IN THE LIST:\n");

        while(temp != NULL)
        {
            printf("DATA of %d node = %d\n", n, temp->data);

            n++;

            /* Move pointer to next node */
            temp = temp->next;
        }
    }
}


/**
 * Reverse order of the doubly linked list
 */
void reverseList()
{
    struct node *current, *temp;

    current = head;
    while(current != NULL)
    {
        /*
         * Swap the previous and next address fields of current node
         */
        temp = current->next;
        current->next = current->prev;
        current->prev = temp;

        /* Move the current pointer to next node which is stored in temp */
        current = temp;
    }
    
    /* 
     * Swap the head and last pointers
     */
    temp = head;
    head = last;
    last = temp;

    printf("LIST REVERSED SUCCESSFULLY.\n");
}



// #include <stdio.h>
// #include <stdlib.h>

// struct node
// {
//      int data;
//      struct node *next;
//      struct node *pre;
// }*head,*p;

// void linklisttreversal(struct node *ptr)
// {
//      struct node* last;
//      printf("\nTraversal in forward direction \n");
//      while (ptr != NULL)
//      {
//           printf("%d ", ptr->data);
//           last = ptr;
//           ptr = ptr->next;
//      }
//      printf("\n");
//      printf("\nTraversal in reverse direction \n");
//      while (last!=NULL)
//      {
//           printf("%d ",last->data);
//           last = last->pre;
//      }
// }

// struct node *createDoubly_linklist(struct node *head, int n)
// {
//      struct node *temp;
//      for (int i = 0; i < n; i++)
//      {
//           temp = (struct node *)malloc(sizeof(struct node));
//           printf("Enter data: ");
//           scanf("%d", &temp->data);
//           temp->pre = NULL;
//           temp->next = NULL;
//           if (head == NULL)
//           {
//                head = p = temp;
//           }
//           else
//           {
//                p->next = temp;
//                temp->pre = p;
//                p=temp;
//           }
//      }
//      return head;
// }

// struct node* rev_doubly_linklist(struct node * head){
//      struct node * temp=head;
//      struct node * np=NULL;
//      while (temp!=NULL)
//      {
//           np=temp->next;
//           temp->next=temp->pre;
//           temp->pre=np;
//           temp=np;
//           // temp=temp->next;
//           // p=p->next;
//      }
//      np=head;
//      head=p;
//      p=np;
     
//      return head;
// }

// int main()
// {
//      int n;
//      printf("How many nodes u want: ");
//      scanf("%d", &n);
//      createDoubly_linklist(head, n);
//      linklisttreversal(head);
//      printf("\nAfter rev\n");
//      rev_doubly_linklist(head);
//      linklisttreversal(head);
//      return 0;
// }