122. Best Time to Buy and Sell Stock II

这道题里面可以买卖股票多次。

这里我加入了sell price。
基本上就是有这个特性：如果看到价格比卖出价格低，就应该换手，这样肯定比不换手得到的利润要高。
Greedy算法就可以解决这个问题。

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        # Initially looks like that this is a DP problem because the past results need to be saved
        # We don't know which case is better, 1,3,2,5 or 1-3,2-5, or 1-5
        # BUT we can always get a cheaper buying price than the selling price, it's always good to switch hands.
        # This is greedy algorithm.
        if not prices: return 0
        max_profit = max_profit_round = 0
        buying_price = prices[0]
        selling_price = 0
        for price in prices:
            #print("price: %d, buying price: %d, selling price: %d" % (price, buying_price, selling_price))
            if price < buying_price:
                buying_price = price
                #print("updating buying price to %d" % price)
            elif price > buying_price:
                if price-buying_price > max_profit_round:
                    selling_price = price
                    max_profit_round = price-buying_price
                    #print("Updating selling price to %d" % price)
            
            if price < selling_price:   # 这里，一定是IF，不是elif，算是比前一题附加一点。
                max_profit += max_profit_round
                max_profit_round = 0
                buying_price = price
                #print("Refresh my stock price to %d, profit to %d" % (price, max_profit))
                
        max_profit += max_profit_round
        
        return max_profit

标签：Sell,Buy,profit,max,price,II,selling,round,buying
来源： https://blog.csdn.net/SpanningWings/article/details/101146168