/usr/share/slib/priorque.scm is in slib 3b1-3.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 | ;;;; "priorque.scm" priority queues for Scheme.
;;; Copyright (C) 1992, 1993, 1994, 1995, 1997 Aubrey Jaffer
;
;Permission to copy this software, to modify it, to redistribute it,
;to distribute modified versions, and to use it for any purpose is
;granted, subject to the following restrictions and understandings.
;
;1. Any copy made of this software must include this copyright notice
;in full.
;
;2. I have made no warranty or representation that the operation of
;this software will be error-free, and I am under no obligation to
;provide any services, by way of maintenance, update, or otherwise.
;
;3. In conjunction with products arising from the use of this
;material, there shall be no use of my name in any advertising,
;promotional, or sales literature without prior written consent in
;each case.
;;@code{(require 'priority-queue)}
;;@ftindex priority-queue
;;
;;@noindent
;;This algorithm for priority queues is due to
;;@cite{Introduction to Algorithms}
;;by T. Cormen, C. Leiserson, R. Rivest.
;;1989 MIT Press.
(require 'record)
;; Record type.
(define heap:rtd (make-record-type "heap" '(array size heap<?)))
;; Reference an element.
(define heap:ref
(let ((ra (record-accessor heap:rtd 'array)))
(lambda (a i)
(vector-ref (ra a) (+ -1 i)))))
;; Set an element.
(define heap:set!
(let ((ra (record-accessor heap:rtd 'array)))
(lambda (a i v)
(vector-set! (ra a) (+ -1 i) v))))
;; Exchange two elements.
(define heap:exchange
(let ((aa (record-accessor heap:rtd 'array)))
(lambda (a i j)
(set! i (+ -1 i))
(set! j (+ -1 j))
(let* ((ra (aa a))
(tmp (vector-ref ra i)))
(vector-set! ra i (vector-ref ra j))
(vector-set! ra j tmp)))))
(define heap:heap<? (record-accessor heap:rtd 'heap<?))
(define heap:set-size!
(let ((aa (record-accessor heap:rtd 'array))
(am (record-modifier heap:rtd 'array))
(sm (record-modifier heap:rtd 'size)))
(lambda (a s)
(let ((ra (aa a)))
(if (> s (vector-length ra))
(let ((nra (make-vector (+ s (quotient s 2)))))
(do ((i (+ -1 (vector-length ra)) (+ -1 i)))
((negative? i) (am a nra))
(vector-set! nra i (vector-ref ra i)))))
(sm a s)))))
(define (heap:parent i) (quotient i 2))
(define (heap:left i) (* 2 i))
(define (heap:right i) (+ 1 (* 2 i)))
(define (heap:heapify a i)
(let* ((l (heap:left i))
(r (heap:right i))
(largest (if (and (<= l (heap:length a))
((heap:heap<? a) (heap:ref a i) (heap:ref a l)))
l
i)))
(cond ((and (<= r (heap:length a))
((heap:heap<? a) (heap:ref a largest) (heap:ref a r)))
(set! largest r)))
(cond ((not (= largest i))
(heap:exchange a i largest)
(heap:heapify a largest)))))
;;;; Externals
;;@body
;;Returns a binary heap suitable which can be used for priority queue
;;operations.
(define make-heap
(let ((cstr (record-constructor heap:rtd)))
(lambda (pred<?)
(cstr (make-vector 4) 0 pred<?))))
;;@args heap
;;Returns the number of elements in @1.
(define heap-length (record-accessor heap:rtd 'size))
;;@args heap item
;;Inserts @2 into @1. @2 can be inserted multiple
;;times. The value returned is unspecified.
(define (heap-insert! a key)
(define i (+ 1 (heap:length a)))
(heap:set-size! a i)
(do ()
((not (and (> i 1)
((heap:heap<? a) (heap:ref a (heap:parent i)) key))))
(heap:set! a i (heap:ref a (heap:parent i)))
(set! i (heap:parent i)))
(heap:set! a i key))
;;@args heap
;;Returns the item which is larger than all others according to the
;;@var{pred<?} argument to @code{make-heap}. If there are no items in
;;@1, an error is signaled.
(define (heap-extract-max! a)
(if (< (heap:length a) 1)
(slib:error "heap underflow" a))
(let ((max (heap:ref a 1)))
(heap:set! a 1 (heap:ref a (heap:length a)))
(heap:set-size! a (+ -1 (heap:length a)))
(heap:heapify a 1)
max))
;; Internal protect.
(define heap:length heap-length)
|