71 lines
2.8 KiB
Scheme
71 lines
2.8 KiB
Scheme
;;; b-tree.scm - a B-tree for Xanadu
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;;;
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;;; Copyright (c) 2011-2012 Johan Ceuppens
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;;;
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;;; All rights reserved.
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;;;
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;;; Redistribution and use in source and binary forms, with or without
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;;; modification, are permitted provided that the following conditions
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;;; are met:
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;;; 1. Redistributions of source code must retain the above copyright
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;;; notice, this list of conditions and the following disclaimer.
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;;; 2. Redistributions in binary form must reproduce the above copyright
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;;; notice, this list of conditions and the following disclaimer in the
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;;; documentation and/or other materials provided with the distribution.
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;;; 3. The name of the authors may not be used to endorse or promote products
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;;; derived from this software without specific prior written permission.
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;;;
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;;; THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
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;;; IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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;;; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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;;; IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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;;; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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;;; NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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;;; DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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;;; THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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;;; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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;;; THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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(define (vector-median v)
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(let ((len (ceiling (/ (vector-length v) 2))))
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(let ((retl (make-vector len))
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(retr (make-vector len)))
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(do ((i 0 (+ i 1)))
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((= i len) (list retl retr))
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(vector-set! retl i (vector-ref v i))
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(vector-set! retr i (vector-ref v (- len (+ i 1))))
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)))
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(define (make-b-tree)
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(let ((*tree (make-vector 0)))
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(define (goto-left-node str i tree)
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(cond ((= (vector-length tree) i) (display "null node") (vector-set! tree i str))
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(else #f)))
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(define (grow-up upper-node)
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(cond ((eq? node *tree)
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(set! *tree (vector-median *tree
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(define (add-rec str tree upper-node)
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(do ((i 0 (+ i 1)))
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((eq? i (vector-length tree))
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(grow-up upper-node)
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(let ((vi (vector-ref tree i)))
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(cond ((string<=? str vi)
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0)
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((string>=? str vi)
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(grow-down))
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((string=? str vi)
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(set! i (vector-length tree)))
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(else (display "never reached."))))
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))
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(define (add str)
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(add-rec *tree *tree))
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(define (dispatch msg)
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(cond ((eq? msg 'add) add)
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(else (display "b-tree : message not understood."))))
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dispatch))
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