'''

class Solution(object):

def climbStairs(self, n):

```
if n <= 1: return 1
# previous and current
pre = 1
cur = 1
# fibonacci f(n) = f(n-1) + f(n-2)
for i in range(2,n+1):
temp = cur
cur = cur + pre
pre = temp
return cur
```

'''