typedef void *Pointer;
typedef int (*CmpFunc)(Pointer data1, Pointer data2);

typedef struct tPriorityQueue {
    /* ... */
} PriorityQueue;

/* Create empty priority queue. */
void pq_create(PriorityQueue *pq, CmpFunc cmp);

/* Destroy priority queue and free its memory. */
void pq_destroy(PriorityQueue *pq);

/* Add new value into the priority queue. */
void pq_insert(PriorityQueue *pq, Pointer value);

/* Delete maximum value from the priority queue and return it. */
Pointer pq_delete_maximum(PriorityQueue *pq);

/* Return non-zero value if the priority queue is not empty. */
int pq_is_empty(PriorityQueue *pq);