方案改变树值 [英] Scheme changing tree values

问题描述

我需要实现一个叫做 inverse-tree 的过程来接收一棵树其节点数据值为数字和布尔值，并返回等效值其节点满足以下条件的树:

I need to implement a procedure called inverse-tree that receives a tree whose nodes data values are numbers and booleans and returns the equivalent tree whose nodes satisfy the following:

• 如果原始树的等价节点是一个数字，那么结果树的节点是-1·那个节点值
• 如果原始树的等效节点是布尔值，则结果树的节点是该节点值的逻辑非

示例:

> (inverse-tree ’())
’()
> (inverse-tree ’(5))
’(-5)
> (inverse-tree ’(0))
’(0)
> (inverse-tree ’(#f))
’(#t)
> (inverse-tree ’(#t))
’(#f)
> (inverse-tree ’(-5 (1 (-2) (3) (#f)) (#t)))
’(5 (-1 (2) (-3) (#t)) (#f))

Scheme 中(可能是空的或不完整的)树的表示如下:每个嵌套级别的第一个元素表示子树的根.其余元素是子元素(当然，每个元素都是一棵树).叶子由只有一个元素(叶子值)的列表表示.一个完全空的树由空列表表示.

The representation of a (possibly empty or non-complete) tree in Scheme is as follows: the first element in every nesting level represents the root of the sub-tree. The rest of the elements are the children (each of them is a tree, of course). A leaf is represented by a list with only one element (the leaf value). A completely empty tree is represented by the empty list.

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推荐答案

经过大量挖掘和更好地理解语法后，我想出了一个简单的 1 函数解决方案:

After a lot of digging and understanding the syntax better I cam up with a simple 1 function solution:

(define (inverse-tree tree)
  (cond ((eq? '() tree) '())
        ((pair? tree) 
         (cons (inverse-tree (car tree))
                    (inverse-tree (cdr tree))))
        (else ((lambda(x) (if (boolean? x) (not x) (- x))) tree))))

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