source: branches/f4grobner/priority-queue.lisp@ 423

;;; -*-  Mode: Lisp; Package: Maxima; Syntax: Common-Lisp; Base: 10 -*- 

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;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>          

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(in-package :ngrobner)



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;;

;; A conventional implementation of priority queues based on heaps

;;

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(defparameter *priority-queue-allocation-size* 16)



(defun priority-queue-make-heap (&key (element-type 'fixnum))

  (make-array *priority-queue-allocation-size* :element-type element-type :fill-pointer 1

              :adjustable t))



(defstruct (priority-queue (:constructor priority-queue-construct))

  (heap (priority-queue-make-heap))

  test)



(defun make-priority-queue (&key (element-type 'fixnum)

                            (test #'<=)

                            (element-key #'identity))

  (priority-queue-construct

   :heap (priority-queue-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)

  (priority-queue-heap-insert (priority-queue-heap pq) item (priority-queue-test pq)))



(defun priority-queue-remove (pq)

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



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

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



(defun priority-queue-size (pq)

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



(defun priority-queue-upheap (a k

               &optional

               (test #'<=)

               &aux  (v (aref a k)))

  (declare (fixnum k))

  (assert (< 0 k (fill-pointer a)))

  (loop

   (let ((parent (ash k -1)))

     (when (zerop parent) (return))

     (unless (funcall test (aref a parent) v)

       (return))

     (setf (aref a k) (aref a parent)

           k parent)))

  (setf (aref a k) v)

  a)



    

(defun priority-queue-heap-insert (a item &optional (test #'<=))

  (vector-push-extend item a)

  (priority-queue-upheap a (1- (fill-pointer a)) test))



(defun priority-queue-downheap (a k

                 &optional

                 (test #'<=)

                 &aux  (v (aref a k)) (j 0) (n (fill-pointer a)))

  (declare (fixnum k n j))

  (loop

   (unless (<= k (ash n -1))

     (return))

   (setf j (ash k 1))

   (if (and (< j n) (not (funcall test (aref a (1+ j)) (aref a j))))

       (incf j))

   (when (funcall test (aref a j) v)

     (return))

   (setf (aref a k) (aref a j)

         k j))

  (setf (aref a k) v)

  a)



(defun priority-queue-heap-remove (a &optional (test #'<=) &aux (v (aref a 1)))

  (when (<= (fill-pointer a) 1) (error "Empty queue."))

  (setf (aref a 1) (vector-pop a))

  (priority-queue-downheap a 1 test)

  (values v a))



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

  (<= (fill-pointer a) 1))