Python solution

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        def maxProfit(self, prices, fee):
            :type prices: List[int]
            :type fee: int
            :rtype: int
            # two states:
            # max profit when the last action was a buy (does not need to be exactly on that date)
            # max profit when the last action was a sell 
            s0 = -prices[0]
            s1 = 0
            for price in prices:
                # could hold given s0, or buy given s1
                f0 = max(s0, s1 - price)
                # hold or sell given s0
                f1 = max(s1, s0 + price - fee)
                s0, s1 = f0, f1
            return s1

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    @nicksun said in Python solution:

    s1 - price

    Hi Nicksun,
    Could you explain to me the key points to solve this problem?
    I don't understand your code though it seems so simple and neat.
    What is s0 and s1?
    Can you elaborate on how you code this problem
    Thank you

  • 0

    @Song_on_the_road Yeah so this is a dp problem. You want to track two states, last action was buy/sell. Note if you have buy, noAction, noAction then it is treated as last action was buy. s0 and s1 are the initial states: if you buy, your net profit is -prices[0] and since you cannot sell initially, s1=0. The lines in the for loop are basically how you update your profit. Whenever you buy, you subtract off the current price and similarly for the sell.

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