fibonacci.go

package main

import (
	"fmt"
)

func main() {
	fmt.Println(fibonacci1(10)) // 55
	fmt.Println(fibonacci2(10)) // 55
	fmt.Println(fibonacci3(10)) // 55
}

func fibonacci1(n int) int {
	a, b := n%2, 1

	for i := 0; i < n/2; i++ {
		a += b
		b += a
	}

	return a
}

func fibonacci2(n int) int {
	if n < 2 {
		return n
	}

	a, b := 0, 1

	for i := 0; i < n; i++ {
		next := a + b
		a, b = b, next
	}

	return a
}

func fibonacci3(n int) int {
	if n < 2 {
		return n
	}

	return fibonacci3(n-2) + fibonacci3(n-1)
}