题目：

题解：

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        if not prices:
            return 0
        
        n = len(prices)
        f0, f1, f2 = -prices[0], 0, 0
        for i in range(1, n):
            newf0 = max(f0, f2 - prices[i])
            newf1 = f0 + prices[i]
            newf2 = max(f1, f2)
            f0, f1, f2 = newf0, newf1, newf2
        
        return max(f1, f2)