sicp 2.27

最新推荐文章于 2017-01-13 11:32:04 发布

最新推荐文章于 2017-01-13 11:32:04 发布 · 132 阅读

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本文介绍了一种名为 deep-reverse 的过程实现，该过程不仅能够反转列表的元素顺序，还能递归地反转所有子列表的内容。通过两个定义清晰的 Scheme 函数实现这一功能，并给出具体的例子进行说明。

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Exercise 2.27. Modify your reverse procedure of exercise 2.18 to produce a deep-reverse procedure that takes a list as argument and returns as its value the list with its elements reversed and with all sublists deep-reversed as well. For example,

(define x (list (list 1 2) (list 3 4))) x ((1 2) (3 4)) (reverse x) ((3 4) (1 2)) (deep-reverse x) ((4 3) (2 1))

(define (reverse items)
  (if (null? items)
      '()
      (append (reverse (cdr items)) (list (car items)))))

(define (deep-reverse items)
  (if (null? items)
      '()
      (if (list? (car items))
          (append (deep-reverse (cdr items)) (list (deep-reverse (car items))))
          (append (deep-reverse (cdr items)) (list (car items))))))

(define x (list (list 1 2) (list 3 4)))
(reverse x)
(deep-reverse x)

((3 4) (1 2))

((4 3) (2 1))