python 斐波那契数列多种方法

方法一 ：函数闭包

#定义斐波那契数列函数
def fib(x):
    back1 , back2 = 1,1
    def get_fib():
        nonlocal back1 , back2
        back1 , back2 = back2 , back1+back2
        print(back1,end = "")
    return get_fib
n = int(input('请输入需要几位斐波那契数列:'))
# 利用函数闭包调用斐波那契函数
def my_fib(n):
    f = fib()
    for i in range(n):
        f()
my_fib(n)
 

方法二：迭代方法

def func(n):
    a = 1
    b = 1
    c = 1
# 1，1，2 a=1 , b = 1 c = a+b 然后往后挪
    while n > 2:
        c = a + b
        a = b 
        b = c 
        n -= 1
    print(c)
func(5) 

方法三：递归函数

def fib(n):
    if n == 1 or n == 2:
        return 1 
    else:
        return fib(n-1) + fib(n-2)
 
fib(5)

方法四：效率更高 

def tailFibRec(n,x,y):
  if n == 1 or n == 2:
      return y 
  else:
      return tailFibRec(n-1,y,x+y)
tailFibRec(12,1,1)

利用timeit​​​​​​​测量几种方法耗费的时间

# 导入timeit
import timeit
 
def fibRecur(n):
    if n == 1 or n == 2:
        return 1
    else:
        return fibRecur(n-1) + fibRecur(n-2)
 
def tailFibRecur(n, x, y):
    if n == 1 or n == 2:
        return y
    else:
        return tailFibRecur(n-1, y, x+y)
 
def fibIter(n):
    a, b, c = 1, 1, 1
    while n > 2:
        c = a + b
        a = b
        b = c
        n -= 1
    return c
FR = timeit.timeit("fibRecur(12)",setup = "from __main __ import fibRecur")
print(f"普通递归函数调用的时间:{FR.2f}秒)"