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搜索并替换列表中的 n 元素 - 方案

发布于 2024-10-09 08:42:52 字数 52 浏览 0 评论 0原文

在执行此类代码时遇到问题，无法弄清楚如何搜索元素（a）并用（b）替换i，该怎么做？提前谢谢

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诺曦 2024-10-16 08:42:52

从一个清单开始。如果是空的，就留下它。如果第一个元素是列表，那么您想递归地调用您的函数。如果第一个元素等于您搜索的元素，则将替换替换为对列表其余部分的函数的递归调用 - 您需要继续搜索。如果前面的条件都不成立，则将第一个元素用于对列表其余部分的函数进行递归调用。

(define (find-replace a b list)
 (cond
  ((null? list) '())
  ((list? (car list)) (cons (find-replace a b (car list)) (find-replace a b (cdr list))))
  ((eq? (car list) a) (cons b (find-replace a b (cdr list))))
  (else
   (cons (car list) (find-replace a b (cdr list))))))

Start with a list. If it's empty, leave it. If the first element is a list, then you want to call your function recursively. If the first element is equal to what your searching for, cons the replacement onto a recursive call of your function on the rest of the list- you need to keep searching. If none of the earlier conditions are true, cons the first element on to a recursive call of your function for the rest of the list.

(define (find-replace a b list)
 (cond
  ((null? list) '())
  ((list? (car list)) (cons (find-replace a b (car list)) (find-replace a b (cdr list))))
  ((eq? (car list) a) (cons b (find-replace a b (cdr list))))
  (else
   (cons (car list) (find-replace a b (cdr list))))))

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金兰素衣 2024-10-16 08:42:52

试试这个函数：

(define subst
  (lambda (new old l)
    (cond
     ((null? l) (quote ()))
     ((atom? (car l))
      (cond
       ((eq? (car l) old) (cons new
                                (subst new old (cdr l))))
       (else (cons (car l)
                   (subst new old (cdr l))))))
     (else (cons (subst new old (car l))
                 (subst new old (cdr l)))))))

这将搜索 S 表达式列表，并将每次出现的 old 替换为 new 的出现。

Try this function:

(define subst
  (lambda (new old l)
    (cond
     ((null? l) (quote ()))
     ((atom? (car l))
      (cond
       ((eq? (car l) old) (cons new
                                (subst new old (cdr l))))
       (else (cons (car l)
                   (subst new old (cdr l))))))
     (else (cons (subst new old (car l))
                 (subst new old (cdr l)))))))

This will search through a list of S expressions and substitute every occurrence of old with an occurrence of new.

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