70. Climbing Stairs

Description

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 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.

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Example 1:

Input: 2

Output: 2

Explanation: There are two ways to climb to the top.

1. 1 step + 1 step

2. 2 steps

Example 2 :

Input: 3

Output: 3

Explanation: There are three ways to climb to the top.

1. 1 step + 1 step + 1 step

2. 1 step + 2 steps

3. 2 steps + 1 step

class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        way=[1,1]
        for i in range(n-1):
            tmp=way[1]
            way[1]+=way[0]
            way[0]=tmp
        return way[1]