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一、121. 买卖股票的最佳时机

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

二、122.买卖股票的最佳时机II

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

标准dp写法：

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