new_contents: # Time:  O(n)
  # Space: O(1)
  
  # On a staircase, the i-th step has some non-negative cost cost[i] assigned (0 indexed).
  #
  # Once you pay the cost, you can either climb one or two steps.
  # You need to find minimum cost to reach the top of the floor,
  # and you can either start from the step with index 0, or the step with index 1.
  #
  # Example 1:
  # Input: cost = [10, 15, 20]
  # Output: 15
  # Explanation: Cheapest is start on cost[1], pay that cost and go to the top.
  # Example 2:
  # Input: cost = [1, 100, 1, 1, 1, 100, 1, 1, 100, 1]
  # Output: 6
  # Explanation: Cheapest is start on cost[0], and only step on 1s, skipping cost[3].
  # Note:
  #  - cost will have a length in the range [2, 1000].
  #  - Every cost[i] will be an integer in the range [0, 999].
  
  class Solution(object):
      def minCostClimbingStairs(self, cost):
          """
          :type cost: List[int]
          :rtype: int
          """
          dp = [0] * 3
          for i in reversed(xrange(len(cost))):
              dp[i%3] = cost[i] + min(dp[(i+1)%3], dp[(i+2)%3])
          return min(dp[0], dp[1])
  
subject: Create min-cost-climbing-stairs.py