题目：

题解：

class Solution {
public:int maxProfit(vector<int>& prices) {int n = prices.size();int buy1 = -prices[0], sell1 = 0;int buy2 = -prices[0], sell2 = 0;for (int i = 1; i < n; ++i) {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;}
};