;;; -*-  Mode: Lisp -*- 
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;;;                                                                              
;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>		 
;;;  		       								 
;;;  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.					 
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;;;  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.				 
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;;;  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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.	 
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;;
;; A conventional implementation of priority queues based on heaps
;;
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(defpackage "PRIORITY-QUEUE"
  (:use :cl :heap)
  (:export "PRIORITY-QUEUE"
	   "MAKE-PRIORITY-QUEUE"
	   "PRIORITY-QUEUE-INSERT"
	   "PRIORITY-QUEUE-REMOVE"
	   "PRIORITY-QUEUE-EMPTY-P"
	   "PRIORITY-QUEUE-SIZE"
	   ))

(in-package :priority-queue)

(defstruct (priority-queue (:constructor priority-queue-construct))
  (heap (make-heap))
  test)

(defun make-priority-queue (&key (element-type 'fixnum)
			    (test #'<=)
			    (element-key #'identity))
  (priority-queue-construct
   :heap (make-heap :element-type element-type)
   :test #'(lambda (x y) (funcall test (funcall element-key y) (funcall element-key x)))))
  
(defun priority-queue-insert (pq item)
  (heap-insert (priority-queue-heap pq) item (priority-queue-test pq)))

(defun priority-queue-remove (pq)
  (heap-remove (priority-queue-heap pq) (priority-queue-test pq)))

(defun priority-queue-empty-p (pq)
  (heap-empty-p (priority-queue-heap pq)))

(defun priority-queue-size (pq)
  (fill-pointer (priority-queue-heap pq)))