Ninety-Nine Racket Problems

99-problems.rkt

#lang plai-typed

; Problem 1
(define (my-last list)
  (if (<= (length list) 1)
      list
      (my-last (rest list))))

;(test (my-last empty) empty)
;(test (my-last (list 1)) (list 1))
;(test (my-last (list 1 2 3)) (list 3))

; Problem 2
(define (my-but-last list)
  (if (<= (length list) 2)
      list
      (my-but-last (rest list))))

;(test (my-but-last empty) empty)
;(test (my-but-last (list 1)) (list 1))
;(test (my-but-last (list 1 2 3)) (list 2 3))

; Problem 3
(define (element-at list n)
  (cond
    [(= n 1) (first list)]
    [else (element-at (rest list) (- n 1))]))

; Problem 3
(define (my-length list)
  (if (empty? list)
      0
      (+ 1 (my-length (rest list)))))

; Problem 4
(define (my-reverse list)
  (if (empty? list)
      empty
      (append (my-reverse (rest list)) (cons (first list) empty))))

; Problem 5 (TODO)
(define (is-palindrome list)
  false)