package fib

/**
Fibonacii的几种算法实现
*/

// 直接循环计算
func Fib(n int) int {
    f := [3]int{0,1,1}
    if n < 0 {
        return -1
    }

    if n < 3 {
        return f[n]
    }

    for i := 3; i <= n; i++ {
        f[0],f[1] = f[1],f[2]
        f[2] = f[0] + f[1]
    }

    return f[2]
}

// 略微修改，没有任何数据中间交换哦~~
func Fib2(n int) int {
    f := [2]int{0,1}
    if n < 0 {
        return -1
    }

    if n < 2 {
        return f[n]
    }

    for i := 2; i <= n; i++ {
        f[i&1] += f[(i+1)&1]
    }

    return f[n&1]
}

//递归算法，效率低
func FibRec(n int) int {
    if n < 0 {
        return -1
    }
    return fib_recursion(n)
}

func fib_recursion(n int) int {
    if n < 3 {
        return 1
    }
    return fib_recursion(n-1) + fib_recursion(n-2)
}

//尾递归算法
func FibTail(n int) int {
    if n < 0 {
        return -1
    }

    if n < 3 {
        return 1
    }

    return fib_tail_recursion(n,3)
}

func fib_tail_recursion(n int,a int,b int,begin int) int {
    if n == begin {
        return a + b
    }
    return fib_tail_recursion(n,b,a+b,begin+1)
}

package fib

import (
    //"fmt"
    "testing"
)

func TestFib(t *testing.T) {
    n := 10
    f := Fib(n)
    if f != 55 {
        t.Error("Fib() Failed. Got",f,"Expected 55 ")
    }
}

func TestFib2(t *testing.T) {
    n := 10
    f := Fib2(n)
    if f != 55 {
        t.Error("Fib2() Failed. Got","Expected 55 ")
    }
}

func TestFibRec(t *testing.T) {
    n := 10
    f := FibRec(n)
    if f != 55 {
        t.Error("FibRec() Failed. Got","Expected 55 ")
    }
}

func TestFibTail(t *testing.T) {
    n := 10
    f := FibTail(n)
    if f != 55 {
        t.Error("FibTail() Failed. Got","Expected 55")
    }
}

func BenchmarkFib(b *testing.B) {
    for i := 0; i < b.N; i++ {
        Fib(1000)
    }
}

func BenchmarkFib2(b *testing.B) {
    for i := 0; i < b.N; i++ {
        Fib2(1000)
    }
}

func BenchmarkFibTail(b *testing.B) {
    for i := 0; i < b.N; i++ {
        FibTail(1000)
    }
}

直接递归实在太慢了，无法测试性能。

可以明显看出，直接计算，无交换的算法是最快的。