Leetcode--188. 买卖股票的最佳时机 IV

题目链接：188. 买卖股票的最佳时机 IV

代码1：

二维dp。

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

代码2：

一维dp。

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