题目：
题解：
class Solution:def maxProfit(self, prices: List[int]) -> int:n = len(prices)buy1 = buy2 = -prices[0]sell1 = sell2 = 0for i in range(1, n):buy1 = max(buy1, -prices[i])sell1 = max(sell1, buy1 + prices[i])buy2 = max(buy2, sell1 - prices[i])sell2 = max(sell2, buy2 + prices[i])return sell2
