doubly_xor_linkedlist.c

#include <stdio.h> 
#include <stdlib.h> 
#include <inttypes.h> 
  
// Node structure of a memory  
// efficient doubly linked list 
struct Node 
{ 
    int data; 
    struct Node* npx; /* XOR of next and previous node */
}; 
  
/* returns XORed value of the node addresses */
struct Node* XOR (struct Node *a, struct Node *b) 
{ 
    return (struct Node*) ((uintptr_t) (a) ^ (uintptr_t) (b)); 
} 
  
/* Insert a node at the beginning of the  
   XORed linked list and makes the newly 
   inserted node as head */
void insert(struct Node **head_ref, int data) 
{ 
    // Allocate memory for new node 
    struct Node *new_node = (struct Node *) malloc (sizeof (struct Node) ); 
    new_node->data = data; 
  
    /* Since new node is being inserted at the  
       beginning, npx of new node will always be 
       XOR of current head and NULL */
    new_node->npx = XOR(*head_ref, NULL); 
  
    /* If linked list is not empty, then npx of  
       current head node will be XOR of new node 
       and node next to current head */
    if (*head_ref != NULL) 
    { 
        // *(head_ref)->npx is XOR of NULL and next.  
        // So if we do XOR of it with NULL, we get next 
        struct Node* next = XOR((*head_ref)->npx, NULL); 
        (*head_ref)->npx = XOR(new_node, next); 
    } 
  
    // Change head 
    *head_ref = new_node; 
} 
  
// prints contents of doubly linked 
// list in forward direction 
void printList (struct Node *head) 
{ 
    struct Node *curr = head; 
    struct Node *prev = NULL; 
    struct Node *next; 
  
    printf ("Following are the nodes of Linked List: \n"); 
  
    while (curr != NULL) 
    { 
        // print current node 
        printf ("%d ", curr->data); 
  
        // get address of next node: curr->npx is  
        // next^prev, so curr->npx^prev will be 
        // next^prev^prev which is next 
        next = XOR (prev, curr->npx); 
  
        // update prev and curr for next iteration 
        prev = curr; 
        curr = next; 
    } 
    printf("\n");
} 
  
// Driver program to test above functions 
int main () 
{ 
    /* Create following Doubly Linked List 
    head-->40<-->30<-->20<-->10 */
    struct Node *head = NULL; 
    insert(&head, 10); 
    insert(&head, 20); 
    insert(&head, 30); 
    insert(&head, 40); 
  
    // print the created list 
    printList (head); 
  
    return (0); 
}