122. Best Time to Buy and Sell Stock II

https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/

这道题没什么好说的，只要前一天比今天价格少，就买前一天，卖今天。

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        res = 0
        for i in range(len(prices)-1):
            res+= max(0,prices[i+1]-prices[i])
        return res
        

上面是greedy，那如果我们用buy (hold) & sell 来做呢

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        buy = -prices[0]
        sell = 0
        for price in prices[1:]:
            prevBuy = buy
            buy = max(buy,sell - price)
            sell = max(sell,prevBuy + price)
        return sell