Climbing Stairs

题目：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?

思路：我的解题思想是排列组合的思想，看看路面有多少个2步的走法。代码如下：

class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        count = 1
        if n == 1:
            return 1
        
        num2 = n // 2
        i = 1
        while i <= num2:
            tamp = n - i
            dividend = tamp
            divisor = 1
            #计算被除数
            j = 1
            while j < i:
                dividend *= (tamp-j)
                j += 1
            #计算除数
            j = 1
            while j <= i:
                divisor *= j
                j += 1
                
            count += (dividend / divisor)
            i += 1
            
        return count