Imprime o ultimo elemento e enésimo elemento de uma lista usando Scheme.

exercicios.scm

(define (ultimo lis)
  (cond
    ((null? lis) (display "Lista nula!"))
    ((null? (cdr lis)) (display (car lis)))
    (else (ultimo (cdr lis)))
  )
)
(ultimo '(A B C D E F B A D Z))

(newline)

(define (enesimo n lis)
  (cond
    ((eq? n 1) (display (car lis)))
    (else (enesimo (- n 1) (cdr lis)))
  )
)

(enesimo 3 '(A B C D))

(define (count atm lis)
  (cond
    ((null? lis) 0)
    ((eq? atm (car lis)) (+ 1 (count atm (cdr lis))))
    (else (count atm (cdr lis)))
  )
)

; (count 1 '(1 2 3 4 5 1 1 23 1 45 5))

(define (media lis)
  (/
    (let nsum ([xlis lis])
         (cond
           ((null? xlis) 0)
           (else (+ (car xlis) (nsum (cdr xlis)) ))
          )
    )
  
    (let nmedia ([xlis lis])
        (cond
          ((null? xlis) 0)
          (else (+ 1 (nmedia (cdr xlis))))
    ))
  )
)

(media '(6 4 4 2))

(define (inverter lis)
  (list
    (let n ([nlist lis])
         (cond
           ((not (null? nlist))
                (cons (n (cdr nlist)) (car nlist))
           )
          )
    )
  )
)

(inverter '(1 2 3 4))
; (cons 1 2)

; Checando se existe elemento repetido.
(define (is_repeated tlist)
  (cond
    ((null? tlist) #f)
    ((equal? #t
          (let exist_in ([element (car tlist)] [xlist (cdr tlist)])
            (cond
              ((null? xlist) #f)
              ((equal? element (car xlist)) #t)
              (else (exist_in element (cdr xlist)))
            )
          )
        )
      #t
      )
    (else (is_repeated (cdr tlist)))
  )
)

(is_repeated '(9 2 1 3 4 8 5))