111 lines
3.0 KiB
Scheme
111 lines
3.0 KiB
Scheme
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(load "util.scm")
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(display "\nexample - queue\n")
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(define (front-ptr queue) (car queue))
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(define (rear-ptr queue) (cdr queue))
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(define (set-front-ptr! queue item) (set-car! queue item))
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(define (set-rear-ptr! queue item) (set-cdr! queue item))
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(define (empty-queue? queue) (null? (front-ptr queue)))
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(define (make-queue) (cons '() '()))
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(define (front-queue queue)
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(if (empty-queue? queue)
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(error "FRONT called with an empty queue" queue)
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(car (front-ptr queue))))
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(define (insert-queue! queue item)
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(let ((new-pair (cons item '())))
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(cond ((empty-queue? queue)
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(set-front-ptr! queue new-pair)
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(set-rear-ptr! queue new-pair)
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queue)
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(else
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(set-cdr! (rear-ptr queue) new-pair)
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(set-rear-ptr! queue new-pair)
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queue))))
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(define (delete-queue! queue)
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(cond ((empty-queue? queue)
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(error "DELETE! called with an empty queue" queue))
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(else
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(set-front-ptr! queue (cdr (front-ptr queue)))
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queue)))
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(define q (make-queue))
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(insert-queue! q 'a)
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(insert-queue! q 'b)
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(delete-queue! q)
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(insert-queue! q 'c)
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(insert-queue! q 'd)
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(delete-queue! q)
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(display "\nex-3.21 - print queue\n")
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(define print-queue front-ptr)
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(define q1 (make-queue))
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(assert (print-queue (insert-queue! q1 'a)) '(a))
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(assert (print-queue (insert-queue! q1 'b)) '(a b))
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(assert (print-queue (delete-queue! q1)) '(b))
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(assert (print-queue (delete-queue! q1)) '())
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(display "\nex-3.22 - procedural queue\n")
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(define (make-queue)
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(let ((front-ptr '())
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(rear-ptr '()))
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(define (empty-queue?) (null? front-ptr))
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(define (insert-queue! item)
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(let ((new-pair (cons item '())))
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(cond ((empty-queue?)
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(set! front-ptr new-pair)
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(set! rear-ptr new-pair)
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dispatch)
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(else
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(set-cdr! rear-ptr new-pair)
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(set! rear-ptr new-pair)
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dispatch))))
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(define (delete-queue!)
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(cond ((empty-queue?)
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(error "DELETE! called with an empty queue" queue))
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(else
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(set! front-ptr (cdr front-ptr))
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dispatch)))
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(define (dispatch m)
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(cond
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((eq? m 'insert) insert-queue!)
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((eq? m 'delete) delete-queue!)
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((eq? m 'print) (lambda () front-ptr))
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(else (error "Undefined operation -- DISPATCH-QUEUE" m))))
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dispatch)))
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(define q (make-queue))
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((q 'insert) 'a)
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((q 'insert) 'b)
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((q 'insert) 'c)
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((q 'insert) 'd)
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(assert ((q 'print)) '(a b c d))
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((q 'delete))
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((q 'delete))
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(assert ((q 'print)) '(c d))
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(display "\nex-3.23 - deque\n")
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; A deque (``double-ended queue'') is a sequence in which items can be inserted
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; and deleted at either the front or the rear. Show how to represent deques
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; using pairs, and give implementations of the operations.23 All operations
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; should be accomplished in (1) steps.
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; make-deque
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; empty-deque?
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; front-deque
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; rear-deque
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; front-insert-deque!
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; rear-insert-deque!
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; front-delete-deque!
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; rear-delete-deque!
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