hw05 - TC2006

#lang racket

; reversing a list
(define (my_reverse x)
    (if (null? x)
        x
        #| append rest of the elements (cdr) of my_reverse x
        to the first part of x (car)
        |#
        (append (my_reverse (cdr x)) (list (car x)))
    )
)

; Fibonacci digits
(define (Fib x)
    (cond
      ((zero? x ) 0)
      ((= x 1) 1)
      (else
        (+ (Fib (- x 1)) (Fib (- x 2)))
      )
    )
)

; sum ignoring lists
(define (sum x)
  (cond
    ((null? x) 0)
    ((= (length x) 1)
      (if (number? (car x))
        (car x)
        0
      )
    )
    (else
      (if (number? (car x))
        (+ (car x) (sum (cdr x)))
        (sum (cdr x))
      )
    )
  )
)

; nested sum
(define (nested_sum x)
  (cond
    ((null? x) 0)
    (else
      (if (number? (car x))
        (+ (car x) (nested_sum (cdr x)))
        (+ (nested_sum (car x)) (nested_sum (cdr x)))
      )
    )
  )
)

; remove nested lists
(define (rmv_lists x)
  (cond
    ((null? x) x)
    (else
      (if (not (list? (car x)))
        (append (list (car x)) (rmv_lists (cdr x)))
        (append (rmv_lists (car x)) (rmv_lists (cdr x)))
      )
    )
  )
)

; mean of a list of numbers
; we assume all elements of the input list are numbers
; we also assume there's no nested lists
; we use the previously defined sum function

(define (my_mean x)
  (cond
   ((null? x) (display "Error"))
   (else
    (/ (sum x) (length x))
   )
  )
)



;Test cases
;(my_reverse '(1 2 3 4 5 6))
;(Fib 8)
;(sum '('(1) 2 3 4 5))
;(nested_sum '(1 (2 (3)) (4 (5)) 6))
;(rmv_lists '(1 (((a 2) b) 3) c))
;(my_mean '(18 5.1 7 19.6 20))