/* A custom doubly linked list implemenation */

 # include <stdio.h>

 # include <stdlib.h>

 # include <math.h>

 # include "global.h"

 # include "rand.h"

 /* Insert an element X into the list at location specified by NODE */

 void insert (list *node, int x)

 {

     list *temp;

     if (node==NULL)

     {

         printf("\n Error!! asked to enter after a NULL pointer, hence exiting \n");

         exit();

     }

     temp = (list *)malloc(sizeof(list));

     temp->index = x;

     temp->child = node->child;

     temp->parent = node;

     if (node->child != NULL)

     {

         node->child->parent = temp;

     }

     node->child = temp;

     return;

 }

 /* Delete the node NODE from the list */

 list* del (list *node)

 {

     list *temp;

     if (node==NULL)

     {

         printf("\n Error!! asked to delete a NULL pointer, hence exiting \n");

         exit();

     }

     temp = node->parent;

     temp->child = node->child;

     if (temp->child!=NULL)

     {

         temp->child->parent = temp;

     }

     free (node);

     return (temp);

 }

typedef struct lists

{

    int index;

    struct lists *parent;

    struct lists *child;

} list;