递归简单学习

Python

1.递归

def fn(n):
    if n<2:
        return n
    return fn(n-1) + fn(n-2)

2.尾递归

def fn(n,a,b):
    if n==0: return 0
    if n==1: return a
    return fn(n-1,b,a+b)

 

3.迭代

def fn(n):
    if n==0:
        return 0
    a,b,c = 1, 1, 0
    for i in range(2,n):
        c = a+b
        a = b
        b = c
    return b