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