#ifndef MINPRIORITYQUEUE_DEFINED
#define MINPRIORITYQUEUE_DEFINED

/* File MinPriorityQueue.h.  Header file for a MinPriorityQueue
   containing elements of type PQEntry.  PQEntry must be defined
   on the command line when any source file including MinPriorityQueue.h
   is compiled, e.g.,
       gcc -Wall -DPQEntry=Event MinPriorityQueue.c
   where Event is a structure type.

   In a MinPriorityQueue, a remove operations always removes the
   "smallest element".  Since the elements may be of structure or
   pointer type, we cannot decide which element is smallest by
   comparing elements using <.  The program using a MinPriorityQueue
   must supply a function

         Boolean f( PQEntry a, PQEntry b);

   that returns true if a should be treated as less than b. A
   pointer to this function is then passed to the function
   CreateMinPriorityQueue that creates the MinPriorityQueue.
*/

#ifndef PQEntry
#error Error: PQEntry not defined in the compile command.
#endif

#include "mcs360.h"

typedef struct MinPriorityQueue MinPriorityQueue;

/* createMinPriorityQueue(less) creates a new MinPriorityQueue,
   initializes it to empty, and returns a pointer to it. The argument
   less is a pointer to a function that tells us when one element of
   type PQEntry is treated as less than another; a is treated as less
   that b is less(a,b) is true. */
MinPriorityQueue *CreateMinPriorityQueue( Boolean (*less)(PQEntry,PQEntry));

/* DestroyMinPriorityQueue(pq) frees the dynamic memory used by
   MinPriorityQueue pq. */
void DestroyMinPriorityQueue( MinPriorityQueue *pq);

/* add(item,pq) adds item to MinPriorityQueue pq. */
void add( PQEntry item, MinPriorityQueue *pq);

/* removeMin(pq) removes a "smallest" element on MinPriorityQueue pq,
   and returns it.  Here a "smallest" element on pq is an element x such
   that less(y,x) is false for all y on pq. */
PQEntry removeMin( MinPriorityQueue *pq);

/* min(pq) returns a "smallest" element (as defined above) on
   MinPriorityQueue pq, without removing it from pq. */
PQEntry min( const MinPriorityQueue *pq);

/* empty(pq) returns true if MinPriorityQueue pq is empty.*/
Boolean empty( const MinPriorityQueue *pq);

/* size(pq) returns the number of elements in the MinPriorityQueue pq. */
int size( const MinPriorityQueue *pq);

#endif