网站文章结构变更怎么做301/企业推广语

拿书中的队列表示来看

我们只需要打印队列的头指针，即可以打印出完整的队列，也就是图中红色区域，如果打印q本身，就会多一层序对结构，并且多打印一次尾指针。
附上完整代码

#lang R5RS
(define (make-queue) (cons '() '()))
(define (front-ptr queue) (car queue))
(define (rear-ptr queue) (cdr queue))
(define (set-front-ptr! queue item) (set-car! queue item))
(define (set-rear-ptr! queue item) (set-cdr! queue item))
(define (empty-queue? queue) (null? (front-ptr queue)))
(define (front-queue queue)(if (empty-queue? queue)(display "FRONT called with an empty queue" queue)(car (front-ptr queue))))
(define (insert-queue! queue item)(let ((new-pair (cons item '())))(cond ((empty-queue? queue)(set-front-ptr! queue new-pair)(set-rear-ptr! queue new-pair)queue)(else(set-cdr! (rear-ptr queue) new-pair)(set-rear-ptr! queue new-pair)queue))))
(define (delete-queue! queue)(cond ((empty-queue? queue)(display "DELETE! called with an empty queue" queue))(else(set-front-ptr! queue (cdr (front-ptr queue)))queue)))
(define (print-queue queue)(display (car queue))(newline))(define q1 (make-queue))
(insert-queue! q1 'a)
(display q1)
(newline)
(insert-queue! q1 'b)
(display q1)
(newline)
(delete-queue! q1)
(display q1)
(newline)
(delete-queue! q1)
(display q1)
(newline)(define q2 (make-queue))
(insert-queue! q2 'a)
(print-queue q2)
(insert-queue! q2 'b)
(print-queue q2)
(delete-queue! q2)
(print-queue q2)
(delete-queue! q2)
(print-queue q2)

运行结果

((a) a)
((a b) b)
((b) b)
(() b)
(a)
(a b)
(b)
()