#lang racket
(provide 2nd-max)

;; -------------------------------------------------------------------
;; A functional solution, "Code Golf"-style: one-line!
;; The downside is that it's O(n log n),
;; because it does more work than we need.

(define (2nd-max lon)
  (second (sort lon >)))

;; -------------------------------------------------------------------
;; A functional solution that doesn't sort.
;; It is O(n), but it makes three passes over the list.
;; 
;; (define (2nd-max lon)
;;   (apply max
;;          (remove (apply max lon)
;;                  lon)))

;; -------------------------------------------------------------------

(require rackunit)
(check-equal? (2nd-max '(6 1 2 -3 9 4 -1 2 8 1 2 4))  8)
(check-equal? (2nd-max '(2 3 8 6 6 75 38 3 2))       38)
(check-equal? (2nd-max '(2 3))                        2)
(check-equal? (2nd-max '(2 -1))                      -1)

;; -------------------------------------------------------------------