力扣-12.23-188

参考：https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-iv/solution/dong-tai-gui-hua-by-liweiwei1419-4/

class Solution {
    public int maxProfit(int k, int[] prices) {
        if (prices == null || prices.length == 0) {
            return 0;
        }
        int len = prices.length;
        if (k >= len / 2) {
            int profit = 0;
            for(int i = 1; i < len; i++) {
                if (prices[i] > prices[i - 1]) {
                    profit += prices[i] - prices[i - 1];
                }
            }
            return profit;
        }

        int[][][] dp = new int[len + 1][k + 1][2];
        for (int i = 0; i <= len; i++) {
            for (int j = 0; j <= k; j++) {
                dp[i][j][1] = Integer.MIN_VALUE;
            }
        }

        for (int i = 1; i <= len; i++) {
            for (int j = 1; j <= k; j++) {
                dp[i][j][0] = Math.max(dp[i - 1][j][0], dp[i - 1][j][1] + prices[i - 1]);
                dp[i][j][1] = Math.max(dp[i - 1][j][1], dp[i - 1][j - 1][0] - prices[i - 1]);
            }
        }
        return dp[len][k][0];
    }
}

跑过了！

优化后的：

class Solution {
    public int maxProfit(int k, int[] prices) {
        if (prices == null || prices.length == 0) {
            return 0;
        }
        int len = prices.length;
        if (k >= len / 2) {
            int profit = 0;
            for(int i = 1; i < len; i++) {
                if (prices[i] > prices[i - 1]) {
                    profit += prices[i] - prices[i - 1];
                }
            }
            return profit;
        }

        int[][] dp = new int[k + 1][2];
        for (int j = 0; j <= k; j++) {
            dp[j][1] = Integer.MIN_VALUE;
        }

        for (int price : prices) {
            for (int j = 1; j <= k; j++) {
                dp[j][0] = Math.max(dp[j][0], dp[j][1] + price);
                dp[j][1] = Math.max(dp[j][1], dp[j - 1][0] - price);
            }
        }
        return dp[k][0];
    }
}

写了这题后发现123题可以设置 k=2 即可！！！具体代码请看123题！