关键是要画出状态转移图

然后根据状态转移图来写状态转移方程

class Solution {
public:int maxProfit(vector<int>& prices) {int len = prices.size();vector<vector<int>> dp(len, vector<int>(4, 0));dp[0][0] = -prices[0];for (int i = 1; i < len; i++){dp[i][0] = max(dp[i - 1][0], max(dp[i - 1][1] - prices[i], dp[i - 1][3] - prices[i]));dp[i][1] = max(dp[i - 1][1], dp[i - 1][3]);dp[i][2] = dp[i - 1][0] + prices[i];dp[i][3] = dp[i - 1][2];}return max(dp[len - 1][1], max(dp[len - 1][2], dp[len - 1][3]));}
};

这道题其实就是在买卖股票II的基础上加入一点变化而已，代码框架还是那个框架。

class Solution {
public:int maxProfit(vector<int>& prices, int fee) {vector<vector<int>> dp(prices.size(), vector<int>(2, 0));dp[0][0] = -prices[0] - fee;for (int i = 1; i < prices.size(); i++){dp[i][0] = max(dp[i - 1][0], dp[i - 1][1] - prices[i] - fee);dp[i][1] = max(dp[i - 1][1], dp[i - 1][0] + prices[i]);}return dp[prices.size() - 1][1];}
};