dp08

121. 买卖股票的最佳时机

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

122. 买卖股票的最佳时机 II

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

123. 买卖股票的最佳时机 III

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int k = 2;
        vector<vector<int>> dp(prices.size(), vector<int>(5, 0));
        
        dp[0][1] = -prices[0];
        dp[0][3] = -prices[0];

        for (int i = 1; i < prices.size(); i++) {
            dp[i][0] = dp[i - 1][0];
            dp[i][1] = max(dp[i - 1][1], dp[i - 1][0] - prices[i]);
            dp[i][2] = max(dp[i - 1][2], dp[i - 1][1] + prices[i]);
            dp[i][3] = max(dp[i - 1][3], dp[i - 1][2] - prices[i]);
            dp[i][4] = max(dp[i - 1][4], dp[i - 1][3] + prices[i]); 
        }
        return dp[prices.size() - 1][4];
    }
};