distinct?

distinct.rkt

#lang racket
(require rackunit)

(define (distinct? xs)
  (= (set-count (list->set xs)) (length xs)))

(check-equal? (distinct? '()) #t)
(check-equal? (distinct? '(1)) #t)
(check-equal? (distinct? '(1 2)) #t)
(check-equal? (distinct? '(1 1)) #f)
(check-equal? (distinct? '(1 2 3)) #t)
(check-equal? (distinct? '(1 2 3 3 2)) #f)
(check-equal? (distinct? '(a b)) #t)
(check-equal? (distinct? '(a b a)) #f)
(check-equal? (distinct? '(a b c c)) #f)
(check-equal? (distinct? '(1 2 3 4)) #t)
(check-equal? (distinct? '(1 2 3 4 5)) #t)
(check-equal? (distinct? '(1 (2 3) 4 2 3)) #t)