斐波那契数列实现方式,以及递归和非递归时间对比

 第n个斐波那契数是多少..递归方式

def fib(n):
    if n== -1:
        exit()
    elif n<3:
        return 1
    else:
        return fib(n - 1) + fib(n - 2)
print(fib(100))

 第n个斐波那契数是多少..非递归方式

def fib(n):
    re = [0,1]
    if n <=1:
        return re[n]
    for i in range(2,n+1):
        re.append(re[i-1]+re[i-2])
    return re[n]
print(fib(100))

n以内的斐波那契数都列出来

def fib(n):
    a, b = 1, 1
    while a < n:
        print(a, end=' ')
        a, b = b, a+b
    print()
fib(1000)

最后..递归很好资源.后面时间成指数增加

import datetime

start = datetime.datetime.now()
def fib(n):
    re = [0,1]
    if n <=1:
        return re[n]
    for i in range(2,n+1):
        re.append(re[i-1]+re[i-2])
    return re[n]
print(fib(1000))
end = datetime.datetime.now()
print(end-start)

print("*"*30)

start = datetime.datetime.now()
def fib(n):
    if n== -1:
        exit()
    elif n<3:
        return 1
    else:
        return fib(n - 1) + fib(n - 2)
print(fib(40))

end = datetime.datetime.now()
print(end-start)

结果对照..

43466557686937456435688527675040625802564660517371780402481729089536555417949051890403879840079255169295922593080322634775209689623239873322471161642996440906533187938298969649928516003704476137795166849228875
0:00:00.000999
******************************
102334155
0:00:47.448738

注意,,非递归查的是第1000个,递归查的是第40个..但是时间差距巨大