python 斐波那契数的几种形式

斐波那契 问第n个斐波那契数是多少？
循环实现：

a = 1
b = 1

while 1:
    n = int(input('请输入你要计算第几个斐波那契数：'))
    for i in range(1,n+1):
        if i == 1 or i == 2:
            a = 1
            b = 1
        else:
            a,b=a+b,a
    print(a)

递归实现：

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

print(fib(4))

def fib(n,l=[0]):
    l[0] +=1
    if n == 1 or n == 2:
        l[0] -=1
        return 1,1
    else:
        a,b = fib(n - 1)
        l[0] -= 1
        if l[0] == 0:
            return a+b
        return b,a+b

print(fib(6))