代码随想录中对6种变形做了详细的对比和分析，记录如下，模板是固定的。
121. 买卖股票的最佳时机
class Solution {
public:int maxProfit(vector<int>& prices) {vector<vector<int>> dp(prices.size(), vector<int>(2,0));// dp[i][0]持有股票// dp[i][1]不持有股票dp[0][0] = -prices[0];dp[0][1] = 0;for (int i = 1; i < prices.size(); i++) {dp[i][0] = max(dp[i-1][0], -prices[i]);dp[i][1] = max(dp[i-1][1], dp[i-1][0] + prices[i]);}return dp[prices.size()-1][1];}
};
122. 买卖股票的最佳时机 II
class Solution {
public:int maxProfit(vector<int>& prices) {int len = prices.size();vector<vector<int>> dp(len, vector<int>(2,0));// dp[i][0]持有股票// dp[i][1]不持有股票dp[0][0] = -prices[0];dp[0][1] = 0;for (int i = 1; i < len; i++) {dp[i][0] = max(dp[i-1][0], dp[i-1][1] - prices[i]);dp[i][1] = max(dp[i-1][1], dp[i-1][0] + prices[i]);}return dp[len-1][1];}
};
124. 买卖股票的最佳时机 III
class Solution {
public:int maxProfit(vector<int>& prices) {int len = prices.size();vector<vector<int>> dp(len, vector<int>(5,0));// 5个状态，没有交易，第一次买入，第一次卖出，第二次买入，第二次卖出dp[0][0] = 0;dp[0][1] = -prices[0]; //dp[0][2] = 0;dp[0][3] = -prices[0]; // 与实际意义相符合dp[0][4] = 0;for (int i = 1; i < len; i++) {dp[i][0] = dp[i-1][0];dp[i][1] = max(dp[i-1][0] - prices[i], dp[i-1][1]);dp[i][2] = max(dp[i-1][1] + prices[i], dp[i-1][2]);dp[i][3] = max(dp[i-1][2] - prices[i], dp[i-1][3]);dp[i][4] = max(dp[i-1][3] + prices[i], dp[i-1][4]);}return dp[len-1][4];}
};
188. 买卖股票的最佳时机 IV
class Solution {
public:int maxProfit(int k, vector<int>& prices) {int len = prices.size();vector<vector<int>> dp(len, vector<int>(2*k + 1,0));for (int i = 0; i < k; i++) {dp[0][i*2+1] = -prices[0];}for (int i = 1; i < len; i++) {dp[i][0] = dp[i-1][0];for (int j = 1; j < 2*k + 1; j+=2) {dp[i][j] = max(dp[i-1][j-1] - prices[i], dp[i-1][j]); // bug 一开始prices[i]写成了price[j]dp[i][j+1] = max(dp[i-1][j] + prices[i], dp[i-1][j+1]);}}return dp[len-1][2*k];}
};
714. 买卖股票的最佳时机含手续费
class Solution {
public:int maxProfit(vector<int>& prices, int fee) {int len = prices.size();vector<vector<int>> dp(len, {0,0});dp[0][0] = -prices[0];dp[0][1] = 0;for (int i = 1; i < len; i++) {dp[i][0] = max(dp[i-1][0], dp[i-1][1] - prices[i]);dp[i][1] = max(dp[i-1][1], dp[i-1][0] + prices[i] - fee); //这里计算上手续费即可}return dp[len-1][1];}
};
