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