```
class Solution(object):
def climbStairs(self, n):
"""
:type n: int
:rtype: int
"""
"""
if n==1:
return 1
elif n==2:
return 2
return self.climbStairs(n-1)+self.climbStairs(n-2)
and the leetcode saids this exceed the time limit
but I found that this is a Fibonacci numbers
so I write this iteration process to produce Fibonacci number,
and NOTICE this is not recurssion,it's is iteration
"""
def iterate_fibonacci(a,b,i):
if i>n:
return b
else:
return iterate_fibonacci(b,a+b,i+1)
return iterate_fibonacci(0,1,1)
```