leetcode

class :
    def maxProfit(self, prices: List[int]) -> int:
        days = len(prices)
        if (days <= 1):
            return 0
        else:
            if (sorted(prices) == prices):
                return prices[-1] - prices[0]
            elif (reversed(prices) == prices):
                return 0
            else:
                
                profit = 0
                buy = -1 # 本来是0，但是没想到price还能是0
                sell = -1
                prices.insert(0, float('inf')) # 第一天只考虑买，最后一天只考虑卖
                prices.append(0)
                for i in range(1, days+1):
                    if (prices[i] <= prices[i+1] and prices[i] <= prices[i-1]):
                        buy = prices[i]
                    elif (prices[i] >= prices[i+1] and prices[i] >= prices[i-1]):
                        if (buy != -1): # 只有在buy的前提下，才考虑sell
                            sell = prices[i]

                    if (buy != -1 and sell != -1):
                        profit += (sell - buy)
                        buy = -1
                        sell = -1
                return profit