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source: branches/f4grobner/priority-queue.lisp@ 231

Last change on this file since 231 was 187, checked in by Marek Rychlik, 9 years ago

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1;;; -*- Mode: Lisp; Package: Maxima; Syntax: Common-Lisp; Base: 10 -*-
2;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
3;;;
4;;; Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>
5;;;
6;;; This program is free software; you can redistribute it and/or modify
7;;; it under the terms of the GNU General Public License as published by
8;;; the Free Software Foundation; either version 2 of the License, or
9;;; (at your option) any later version.
10;;;
11;;; This program is distributed in the hope that it will be useful,
12;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
13;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14;;; GNU General Public License for more details.
15;;;
16;;; You should have received a copy of the GNU General Public License
17;;; along with this program; if not, write to the Free Software
18;;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19;;;
20;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
21
22(in-package :ngrobner)
23
24;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
25;;
26;; A conventional implementation of priority queues based on heaps
27;;
28;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
29
30(defparameter *priority-queue-allocation-size* 16)
31
32(defun priority-queue-make-heap (&key (element-type 'fixnum))
33 (make-array *priority-queue-allocation-size* :element-type element-type :fill-pointer 1
34 :adjustable t))
35
36(defstruct (priority-queue (:constructor priority-queue-construct))
37 (heap (priority-queue-make-heap))
38 test)
39
40(defun make-priority-queue (&key (element-type 'fixnum)
41 (test #'<=)
42 (element-key #'identity))
43 (priority-queue-construct
44 :heap (priority-queue-make-heap :element-type element-type)
45 :test #'(lambda (x y) (funcall test (funcall element-key y) (funcall element-key x)))))
46
47(defun priority-queue-insert (pq item)
48 (priority-queue-heap-insert (priority-queue-heap pq) item (priority-queue-test pq)))
49
50(defun priority-queue-remove (pq)
51 (priority-queue-heap-remove (priority-queue-heap pq) (priority-queue-test pq)))
52
53(defun priority-queue-empty-p (pq)
54 (priority-queue-heap-empty-p (priority-queue-heap pq)))
55
56(defun priority-queue-size (pq)
57 (fill-pointer (priority-queue-heap pq)))
58
59(defun priority-queue-upheap (a k
60 &optional
61 (test #'<=)
62 &aux (v (aref a k)))
63 (declare (fixnum k))
64 (assert (< 0 k (fill-pointer a)))
65 (loop
66 (let ((parent (ash k -1)))
67 (when (zerop parent) (return))
68 (unless (funcall test (aref a parent) v)
69 (return))
70 (setf (aref a k) (aref a parent)
71 k parent)))
72 (setf (aref a k) v)
73 a)
74
75
76(defun priority-queue-heap-insert (a item &optional (test #'<=))
77 (vector-push-extend item a)
78 (priority-queue-upheap a (1- (fill-pointer a)) test))
79
80(defun priority-queue-downheap (a k
81 &optional
82 (test #'<=)
83 &aux (v (aref a k)) (j 0) (n (fill-pointer a)))
84 (declare (fixnum k n j))
85 (loop
86 (unless (<= k (ash n -1))
87 (return))
88 (setf j (ash k 1))
89 (if (and (< j n) (not (funcall test (aref a (1+ j)) (aref a j))))
90 (incf j))
91 (when (funcall test (aref a j) v)
92 (return))
93 (setf (aref a k) (aref a j)
94 k j))
95 (setf (aref a k) v)
96 a)
97
98(defun priority-queue-heap-remove (a &optional (test #'<=) &aux (v (aref a 1)))
99 (when (<= (fill-pointer a) 1) (error "Empty queue."))
100 (setf (aref a 1) (vector-pop a))
101 (priority-queue-downheap a 1 test)
102 (values v a))
103
104(defun priority-queue-heap-empty-p (a)
105 (<= (fill-pointer a) 1))
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