/* File: list1d.h
  
   Interface for a doubly linked list implementation 
   of the list ADT in list1.h
*/

#ifndef list1d_h
#define list1d_h


/* Type Definitions */  

typedef struct node_tag {

   char   *item ;  /* we use strings, but item could be anything */

   struct node_tag *prev ;
   struct node_tag *next ;

} node ;

typedef struct {
   node   header ;
   int    count ;
} *list ;


/* Function Prototypes */


/* Make a new list */
list CreateList(void) ;


/* Add item to the end of the list */
void Append(list L, char *item) ;


/* Add item to the beginning of the list */
void Prepend(list L, char *item) ;


/* Does item with key appear on the list? 0=No 1=Yes */
int IsMember(list L, char *key) ;


/* Return the position in the list of the item with key or
   NULL if no such item.

   Note: this time, position is a pointer to the node
   that contains the key, since deletion is easier in
   a doubly linked list.
*/
node *Locate(list L, char *key); 


/* Remove item in given position from the list.
   See note regarding position in documentation for Locate().
*/
void Delete(list L, node *position) ;


/* Add list L2 to the end of list L1.  L2 is destroyed.  */
void Concatenate(list L1, list L2) ;


/* Duplicate of the list. All items and nodes have newly allocated memory.
*/
list ListDup(list L) ;


/* Print the contents of the list. */
void PrintList(list L) ;


/* Free memory allocated to the list. */
void FreeList(list L) ;


/* String in first item returned, or NULL if list is empty */
char *FirstItem(list L) ;


/* String in last item returned, or NULL if list is empty */
char *LastItem(list L) ;


/* Returns number of items in the list */
int CountList(list L) ;


#endif