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/**
* @file pqueue.c
* @brief Implements a priority queue.
* @note Copyright (c) 2015 Richard Cochran <richardcochran@gmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA.
*/
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include "pqueue.h"
#define parent(x) (((1 + (x)) >> 1) - 1)
#define left(x) (((1 + (x)) << 1) - 1)
#define right(x) (((1 + (x)) << 1))
struct pqueue {
int len;
int max;
int (*cmp)(void *a, void *b);
void **data;
};
static int pq_greater(struct pqueue *q, int a, int b)
{
return q->cmp(q->data[a], q->data[b]) > 0 ? 1 : 0;
}
static void heapify(struct pqueue *q, int index)
{
int i_max = index;
int left = left(index);
int right = right(index);
if (left < q->len) {
if (pq_greater(q, left, i_max))
i_max = left;
}
if (right < q->len && pq_greater(q, right, i_max)) {
i_max = right;
}
if (i_max != index) {
void *tmp = q->data[index];
q->data[index] = q->data[i_max];
q->data[i_max] = tmp;
heapify(q, i_max);
}
}
/* public methods */
struct pqueue *pqueue_create(int max_length,
int (*compare)(void *a, void *b))
{
struct pqueue *q = calloc(1, sizeof(*q));
if (!q) {
return NULL;
}
q->len = 0;
q->max = max_length;
q->cmp = compare;
q->data = calloc(max_length, sizeof(void *));
if (!q->data) {
free(q);
return NULL;
}
return q;
}
void pqueue_destroy(struct pqueue *q)
{
free(q->data);
free(q);
}
void *pqueue_extract(struct pqueue *q)
{
void *data;
if (!q->len) {
return NULL;
}
data = q->data[0];
q->data[0] = q->data[q->len - 1];
q->len--;
heapify(q, 0);
return data;
}
int pqueue_insert(struct pqueue *q, void *d)
{
int index;
if (q->len >= q->max) {
void **buf = realloc(q->data, 2 * q->max * sizeof(void *));
if (buf) {
q->data = buf;
q->max *= 2;
} else {
return -ENOMEM;
}
}
index = q->len;
q->len++;
while (index && (q->cmp(q->data[parent(index)], d) < 0)) {
q->data[index] = q->data[parent(index)];
index = parent(index);
}
q->data[index] = d;
return 0;
}
int pqueue_length(struct pqueue *q)
{
return q->len;
}
void *pqueue_peek(struct pqueue *q)
{
return q->len ? q->data[0] : (void *) 0;
}
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