21 lines
698 B
Text
21 lines
698 B
Text
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Rebol [
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title: "Rosetta code: Fibonacci sequence"
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file: %Fibonacci_sequence.r3
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url: https://rosettacode.org/wiki/Fibonacci_sequence
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]
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fibonacci: function/with [
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{Return the Nth Fibonacci number using iterative state advancement.
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Uses a shared block to swap fn and fn-1 in a single expression.}
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number [integer!] "which Fibonacci number to compute (0-indexed)"
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][
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fn-1: 0 ;; F(0)
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fn: 1 ;; F(1)
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loop number advance-fibonacci
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][
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fn: fn-1: 0
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advance-fibonacci: [ fn: fn-1 + fn-1: fn ] ;; simultaneously: new fn = old fn + old fn-1
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]
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probe collect [repeat i 18 [keep fibonacci i]]
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