exercism Scheme exercises

leap.rkt

#lang racket
(require racket/trace)

(define (leap-year? year)
  (if (and (and (div-by-4? year) (div-by-100? year)) (div-by-400? year)) #t 
      (if (and (div-by-4? year) (not (div-by-100? year))) #t #f)))

(define (div-by-4? year)
  (if (= (modulo year 4) 0) #t #f))

(define (div-by-100? year)
  (if (= (modulo year 100) 0) #t #f))

(define (div-by-400? year)
  (if (= (modulo year 400) 0) #t #f))

; modulo code found here
; https://stackoverflow.com/a/60892769/8706936
(define (modulo a b)
  (- a (* b (floor (/ a b)))))

(trace leap-year?)
(leap-year? 1997)
(leap-year? 1900) 
(leap-year? 2000) 
(leap-year? 1966)
(leap-year? 1960)
(leap-year? 2100) 

rna-transcription.rkt

#lang racket
(require racket/trace)

; helper function is used to convert dna into a list
(define (dna->rna dna)
  (define dna-list (string->list dna))
  (define (helper dna-list)
    (cond
      ((= (string-length dna) 0) "")
      ((eqv? dna-list '()) "")
      ((eqv? (car dna-list) #\C) (string-append "G" (helper(cdr dna-list))))
      ((eqv? (car dna-list) #\G) (string-append "C" (helper(cdr dna-list))))
      ((eqv? (car dna-list) #\T) (string-append "A" (helper(cdr dna-list))))
      ((eqv? (car dna-list) #\A) (string-append "U" (helper(cdr dna-list))))
      (else #f))
    )
  (helper dna-list)
  )

(trace dna->rna)
(dna->rna "")
(dna->rna "C")
(dna->rna "G")
(dna->rna "T")
(dna->rna "A")

;UGCACCAGAAUU
(dna->rna "ACGTGGTCTTAA")