Remove multiple characters from a list if they are next to each other in Scheme

Question

I have to make a Dr. Racket program that removes letters from a list if they are following the same letter as itself. For example: (z z f a b b d d) would become (z f a b d

Answer 1

(define (remove-dups x)
   (cond
     [(empty? x) '()]
     [(empty? (cdr x))  (list (car x))]
     [(eq? (car x) (cadr x))  (remove-dups (cdr x))]
     [else  (cons (car x) (remove-dups (cdr x)))]))

(cadr x) is short for (car (cdr x)) in case you didn't know.

Also, pattern matching makes list deconstruction often much more readable. In this case not so much, but it's still better than the other version:

(define (rmv-dups x)
  (match x
    [(list)  (list)]
    [(list a)  (list a)]
    [(cons a (cons a b))  (rmv-dups (cdr x))]
    [__  (cons (car x) (rmv-dups (cdr x)))]))