70. Climbing Stairs

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

Note: Given n will be a positive integer.

 

 

class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n == 0 :
            return 0
        if n == 1 :
            return 1
        if n == 2 :
            return 2
        
        one = 1
        second = 2
        
        for i in range(2,n,1):
            three = one+second
            one = second
            second = three
        
        return three

 

以上