old_contents: """Leetcode 309. Best Time to Buy and Sell Stock with Cooldown
  Medium
  
  URL: https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/
  
  Say you have an array for which the ith element is the price of a given stock on day i.
  
  Design an algorithm to find the maximum profit. You may complete as many transactions
  as you like (ie, buy one and sell one share of the stock multiple times) with the
  following restrictions:
  - You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).
  - After you sell your stock, you cannot buy stock on next day. (ie, cooldown 1 day)
  
  Example:
  Input: [1,2,3,0,2]
  Output: 3 
  Explanation: transactions = [buy, sell, cooldown, buy, sell]
  """
  
  class SolutionDp(object):
      def maxProfit(self, prices):
          """
          :type prices: List[int]
          :rtype: int
          """
          if not prices:
              return 0
  
          n = len(prices)
  
          # Before day i, the max profit ending with buy/sell.
          profit_buys = [0] * n
          profit_sells = [0] * n
  
          profit_buys[0] = -prices[0]
  
          for i in range(1, n):
              profit_buys[i] = max(profit_sells[i - 2] - prices[i], 
                                   profit_buys[i - 1])
              profit_sells[i] = max(profit_buys[i - 1] + prices[i], 
                                    profit_sells[i - 1])
  
          return profit_sells[-1]
  
  
  def main():
      # Output: 3
      prices = [1,2,3,0,2]
      print SolutionDp().maxProfit(prices)
  
  
  if __name__ == '__main__':
      main()
  
new_contents: """Leetcode 309. Best Time to Buy and Sell Stock with Cooldown
  Medium
  
  URL: https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/
  
  Say you have an array for which the ith element is the price of a given stock on day i.
  
  Design an algorithm to find the maximum profit. You may complete as many transactions
  as you like (ie, buy one and sell one share of the stock multiple times) with the
  following restrictions:
  - You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).
  - After you sell your stock, you cannot buy stock on next day. (ie, cooldown 1 day)
  
  Example:
  Input: [1,2,3,0,2]
  Output: 3 
  Explanation: transactions = [buy, sell, cooldown, buy, sell]
  """
  
  class SolutionDp(object):
      def maxProfit(self, prices):
          """
          :type prices: List[int]
          :rtype: int
  
          Time complexity: O(n).
          Space complexity: O(n).
          """
          if not prices:
              return 0
  
          n = len(prices)
  
          # Before day i, the max profit ending with buy/sell.
          profit_buys = [0] * n
          profit_sells = [0] * n
  
          profit_buys[0] = -prices[0]
  
          for i in range(1, n):
              profit_buys[i] = max(profit_sells[i - 2] - prices[i], profit_buys[i - 1])
              profit_sells[i] = max(profit_buys[i - 1] + prices[i], profit_sells[i - 1])
  
          return profit_sells[-1]
  
  
  class SolutionIter(object):
      def maxProfit(self, prices):
          """
          :type prices: List[int]
          :rtype: int
  
          Time complexity: O(n).
          Space complexity: O(1).
          """
          if not prices:
              return 0
  
          profit_buy = -prices[0]
          profit_sell = 0
          profit_buy_prev = 0
          profit_sell_prev = 0
  
          for i in range(1, len(prices)):
              profit_buy_prev = profit_buy
              profit_buy = max(profit_sell_prev - prices[i], profit_buy_prev)
  
              profit_sell_prev = profit_sell
              profit_sell = max(profit_buy_prev + prices[i], profit_sell_prev)
  
          return profit_sell
  
  
  def main():
      # Output: 3
      prices = [1,2,3,0,2]
      print SolutionDp().maxProfit(prices)
      print SolutionIter().maxProfit(prices)
  
  
  if __name__ == '__main__':
      main()
  
subject: Complete iter sol