如何摆脱列表中的重复项，但保持顺序

问题描述

我在 DrRacket 中使用 Intermediate Student with Lambda，我想知道如何在保持顺序的同时删除列表中的重复项.例如 (remove-dup (list 2 5 4 5 1 2)) 会产生 (list 2 5 4 1).到目前为止，我有这个:

I am using Intermediate Student with Lambda in DrRacket, I was wondering how one would remove the duplicates in a list, while keeping the order. For example (remove-dup (list 2 5 4 5 1 2)) would produce (list 2 5 4 1). So far, I have this:

(define (remove-duplicates lst)
  (cond
    [(empty? lst) empty]
    [(member? (first lst) (rest lst))
     (remove-duplicates (rest lst))]
    [else (cons (first lst) (remove-duplicates (rest lst)))]))

，但有一个问题，因为它不保持顺序.有人可以指出我正确的方向吗?谢谢你的时间.

, but there's a problem since it doesn't keep the order. Can someone point me in the right direction? Thanks for your time.

推荐答案

如果您的目标是让功能正常工作，而不是一些家庭作业问题，那么您不需要做任何事情，只需使用 remove-duplicates:

If your goal is to get the functionality working, and not some homework question, then you don't need to do anything, just use remove-duplicates:

Welcome to Racket v5.2.
-> (remove-duplicates (list 2 5 4 5 1 2))
'(2 5 4 1)

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