new_contents: class Solution(object):
      def __init__(self):
          self.dic = {1:1, 2:2}
      def climbStairs(self, n):
          """
          :type n: int
          :rtype: int
          """
          if n not in self.dic:
              self.dic[n] = self.climbStairs(n-1) + self.climbStairs(n-2)
          return self.dic[n]
  
subject: add 70-ClimbingStairs.py