动态规划_leetcode122(股票交易，双状态，状态好难定义)

class Solution(object):
    def maxProfit(self, prices):
        """
        :type prices: List[int]
        :rtype: int
        """

        if  not prices:
            return 0


        buy = [0 for i in range(len(prices))]

        sell = [0 for i in range(len(prices))]

        buy[0] = -prices[0]


        for i in range(1,len(prices)):
            # 状态好难定义
            # 考虑第i天买股票时的最大收益
            buy[i] = max(buy[i-1],sell[i-1]-prices[i])
            # 考虑第i天买股票的最大收益
            sell[i] = max(sell[i-1],buy[i-1] + prices[i])

        return sell[-1]