priorityq-heap.h

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/*
** Author: Eric Veach, July 1994.
**
*/

#ifndef __priorityq_heap_h_
#define __priorityq_heap_h_

/* Use #define's so that another heap implementation can use this one */

#define PQkey        PQHeapKey
#define PQhandle     PQHeapHandle
#define PriorityQ    PriorityQHeap

#define pqNewPriorityQ(leq)   __gl_pqHeapNewPriorityQ(leq)
#define pqDeletePriorityQ(pq) __gl_pqHeapDeletePriorityQ(pq)

/* The basic operations are insertion of a new key (pqInsert),
 * and examination/extraction of a key whose value is minimum
 * (pqMinimum/pqExtractMin).  Deletion is also allowed (pqDelete);
 * for this purpose pqInsert returns a "handle" which is supplied
 * as the argument.
 *
 * An initial heap may be created efficiently by calling pqInsert
 * repeatedly, then calling pqInit.  In any case pqInit must be called
 * before any operations other than pqInsert are used.
 *
 * If the heap is empty, pqMinimum/pqExtractMin will return a NULL key.
 * This may also be tested with pqIsEmpty.
 */
#define pqInit(pq)      __gl_pqHeapInit(pq)
#define pqInsert(pq,key)   __gl_pqHeapInsert(pq,key)
#define pqMinimum(pq)      __gl_pqHeapMinimum(pq)
#define pqExtractMin(pq)   __gl_pqHeapExtractMin(pq)
#define pqDelete(pq,handle)   __gl_pqHeapDelete(pq,handle)
#define pqIsEmpty(pq)      __gl_pqHeapIsEmpty(pq)


/* Since we support deletion the data structure is a little more
 * complicated than an ordinary heap.  "nodes" is the heap itself;
 * active nodes are stored in the range 1..pq->size.  When the
 * heap exceeds its allocated size (pq->max), its size doubles.
 * The children of node i are nodes 2i and 2i+1.
 *
 * Each node stores an index into an array "handles".  Each handle
 * stores a key, plus a pointer back to the node which currently
 * represents that key (ie. nodes[handles[i].node].handle == i).
 */

typedef void *PQkey;
typedef long PQhandle;
typedef struct PriorityQ PriorityQ;

typedef struct { PQhandle handle; } PQnode;
typedef struct { PQkey key; PQhandle node; } PQhandleElem;

struct PriorityQ {
  PQnode *nodes;
  PQhandleElem *handles;
  long      size, max;
  PQhandle  freeList;
  int    initialized;
  int    (*leq)(PQkey key1, PQkey key2);
};
  
PriorityQ   *pqNewPriorityQ( int (*leq)(PQkey key1, PQkey key2) );
void     pqDeletePriorityQ( PriorityQ *pq );

void     pqInit( PriorityQ *pq );
PQhandle pqInsert( PriorityQ *pq, PQkey key );
PQkey    pqExtractMin( PriorityQ *pq );
void     pqDelete( PriorityQ *pq, PQhandle handle );


#define __gl_pqHeapMinimum(pq)   ((pq)->handles[(pq)->nodes[1].handle].key)
#define __gl_pqHeapIsEmpty(pq)   ((pq)->size == 0)

#endif