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#lang racket
(require compatibility/mlist)
;; queue methods
(define (front-ptr q) (mcar q))
(define (rear-ptr q) (mcdr q))
(define (set-front-ptr! q v) (set-mcar! q v))
(define (set-rear-ptr! q v) (set-mcdr! q v))
(define (empty-queue? q) (null? (front-ptr q)))
(define (make-queue) (mcons '() '()))
(define (front-queue q)
(if (empty-queue? q)
(error "FRONT called on empty queue" q)
(mcar (front-ptr q))))
(define (insert-queue! q item)
(let ((new-item (mlist item)))
(cond ((empty-queue? q)
(set-front-ptr! q new-item)
(set-rear-ptr! q new-item)
q)
(else
(set-mcdr! (rear-ptr q) new-item)
(set-rear-ptr! q new-item)
q))))
(define (delete-queue! q)
(cond ((empty-queue? q)
(error "DELETE! called with an empty queue" q))
(else
(set-front-ptr! q (mcdr (front-ptr q)))
q)))
;; 21
(define (print-queue q)
(front-ptr q))
(define q1 (make-queue))
(print-queue (insert-queue! q1 'a))
(print-queue (insert-queue! q1 'b))
(print-queue (delete-queue! q1))
(print-queue (delete-queue! q1))
;; 22
(define (make-queue-obj)
(let ((front-ptr '())
(rear-ptr '()))
(define (set-front-ptr! v)
(set! front-ptr v))
(define (set-rear-ptr! v)
(set! rear-ptr v))
(define (empty-queue?)
(null? front-ptr))
(define (front-queue)
(mcar front-ptr))
(define (insert-queue! item)
(let ((new-pair (mlist item)))
(cond ((empty-queue?)
(set-front-ptr! new-pair)
(set-rear-ptr! new-pair))
(else (set-mcdr! rear-ptr new-pair)
(set-rear-ptr! new-pair)))))
(define (delete-queue!)
(cond ((empty-queue?)
(error "DELETE! called with an empty queue" front-ptr))
(else
(set-front-ptr! (mcdr front-ptr)))))
(define (dispatch m)
(cond ((eq? m 'front-ptr) front-ptr)
((eq? m 'rear-ptr) rear-ptr)
((eq? m 'set-front-ptr!) set-front-ptr!)
((eq? m 'set-rear-ptr!) set-rear-ptr!)
((eq? m 'empty-queue?) empty-queue?)
((eq? m 'front-queue) front-queue)
((eq? m 'insert-queue!) insert-queue!)
((eq? m 'delete-queue!) delete-queue!)
((eq? m 'print-queue) front-ptr)
(else (error "Message note defined on queue" m))))
dispatch))
(define qobj (make-queue-obj))
((qobj 'insert-queue!) 'a)
(qobj 'print-queue)
((qobj 'insert-queue!) 'b)
(qobj 'print-queue)
((qobj 'insert-queue!) 'c)
(qobj 'print-queue)
((qobj 'delete-queue!))
(qobj 'print-queue)
;; 23
(define (make-deque) (mcons '() '()))
;; internal
(define (front-ptr-deque q) (mcar q))
(define (rear-ptr-deque q) (mcdr q))
(define (empty-deque? q) (and (null? (front-ptr-deque q)) (null? (rear-ptr-deque q))))
;; selectors
(define (front-deque q) (mcar (mcar (front-ptr-deque q))))
(define (rear-deque q) (mcar (mcar (rear-ptr-deque q))))
;; mutators
(define (front-insert-deque! q data)
(let ((item (mlist (mlist data))))
(cond ((empty-deque? q) (set-mcar! q item) (set-mcdr! q item) q)
(else (set-mcdr! (mcar (front-ptr-deque q)) item)
(set-mcdr! item (front-ptr-deque q))
(set-mcar! q item)
q))))
(define (rear-insert-deque! q data)
(let ((item (mlist (mlist data))))
(cond ((empty-deque? q) (set-mcar! q item) (set-mcdr! q item) q)
(else (set-mcdr! (mcar item) (rear-ptr-deque q))
(set-mcdr! (rear-ptr-deque q) item)
(set-mcdr! q item)
q))))
(define (rear-delete-deque! q)
(cond ((empty-deque? q) (error "DELETE-REAR deque, tried calling delete on empty deque."))
(else (let ((prev-ptr (mcdr (mcar (rear-ptr-deque q))))
(item (mcar (mcar (rear-ptr-deque q)))))
(set-mcdr! q prev-ptr)
(if (null? prev-ptr)
(set-mcar! q prev-ptr)
(set-mcdr! (rear-ptr-deque q) '()))
item))))
(define (front-delete-deque! q)
(cond ((empty-deque? q) (error "DELETE-FRONT deque, tried calling delete on empty deque."))
(else (let ((next-ptr (mcdr (front-ptr-deque q)))
(item (mcar (mcar (front-ptr-deque q)))))
(set-mcar! q next-ptr)
(if (null? next-ptr)
(set-mcdr! q next-ptr)
(set-mcdr! (mcar (front-ptr-deque q)) '()))
item))))
(define (print-deque q)
(define (rec fn items)
(cond ((null? items) '())
(else (cons (fn (mcar items)) (rec fn (mcdr items))))))
(display (rec (lambda (item)
(mcar item))
(front-ptr-deque q))))
(define dq1 (make-deque))
(rear-insert-deque! dq1 'a)
(rear-insert-deque! dq1 'b)
(rear-insert-deque! dq1 'c)
(print-deque dq1)
(rear-delete-deque! dq1)
(front-delete-deque! dq1)
(rear-delete-deque! dq1)
(print-deque dq1)
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