Fibonacci numbers (Smalltalk)

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Recursion

This simple method uses recursion to return Fibonacci number at receiver position.

fibonacciRecursive
	"calculates Fibonacci number at position number self recursively"
	| num1 num2 res |
	self<0 ifTrue: [self error: 'Not able to calculate Fibonacci number at negative position'].
	self<2 ifTrue: [^1].
	num1 := (self - 1) fibonacciRecursive.
	num2 := (self - 2) fibonacciRecursive.
	res := num1 + num2.
	^res

Iteration

Iterative implementation gives Fibonacci number at receiver position.

fibonacci
	"calculates Fibonacci number at position number self"
	| num1 num2 res |
	self<0 ifTrue: [self error: 'Not able to calculate Fibonacci number at negative position'].
	self<2 ifTrue: [^1].
	num1 := 1.
	num2 := 1.
	self-1 timesRepeat: [res := num1 + num2.
			num2 := num1.
			num1 := res].
	^res

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