28 lines
481 B
Racket
28 lines
481 B
Racket
|
; f(n) = n, when n < 3
|
||
|
|
; f(n) = f(n - 1) + f(n - 2) + f(n - 3), when n >= 3
|
||
|
|
(define fn 15)
|
||
|
|
|
||
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||
|
|
; recursive
|
||
|
|
(define (f-rec n)
|
||
|
|
(if (< n 3)
|
||
|
|
n
|
||
|
|
(+ (+ (f-rec (- n 1))
|
||
|
|
(f-rec (- n 2)))
|
||
|
|
(f-rec (- n 3)))))
|
||
|
|
|
||
|
|
(f-rec fn)
|
||
|
|
|
||
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
||
|
|
; iterative
|
||
|
|
(define (f-iter n)
|
||
|
|
(f-iter-step 2 1 0 n))
|
||
|
|
|
||
|
|
(define (f-iter-step a b c count)
|
||
|
|
(if (< count 3)
|
||
|
|
a
|
||
|
|
(f-iter-step (+ a b c) a b (- count 1))))
|
||
|
|
|
||
|
|
(f-iter fn)
|
||
|
|
|