一、斐波那契数列
1.迭代实现
>>> def fab(n):
n1 =1
n2 =1
n3 =1
if n<0:
return -1
while n-2>0:
n3 = n2 + n1
n1 = n2
n2 = n3
n-=1
return n3
2.递归实现
>>>def fab(n):
if n<1:
print('输入有误!')
return -1
if n==1 or n==2:
return 1
else:
return(fab(n-1) + fab (n-2))
result = fab(20)
print('共有%d对小兔崽子诞生!' %result)