代码随想录算法训练营Day52|动态规划11

代码随想录算法训练营Day52|动态规划11

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买卖股票 难

一、123.买卖股票的最佳时机III

class Solution {
    public int maxProfit(int[] prices) {
        int[] dp = new int[4]; 
        dp[0] = -prices[0];
        dp[1] = 0;
        dp[2] = -prices[0];
        dp[3] = 0;
        for(int i = 1; i <= prices.length; i++){
            dp[0] = Math.max(dp[0], -prices[i-1]);
            dp[1] = Math.max(dp[1], dp[0]+prices[i-1]);
            dp[2] = Math.max(dp[2], dp[1]-prices[i-1]);
            dp[3] = Math.max(dp[3], dp[2]+ prices[i-1]);
        }
        return dp[3];
    }
}

二、188.买卖股票的最佳时机IV

class Solution {
    public int maxProfit(int k, int[] prices) {
        if (prices.length == 0) return 0;
        int len = prices.length;
        int[][] dp = new int[len][k*2 + 1];

        for (int i = 1; i < k*2; i += 2) {
            dp[0][i] = -prices[0];
        }

        for (int i = 1; i < len; i++) {
            for (int j = 0; j < k*2 - 1; j += 2) {
                dp[i][j + 1] = Math.max(dp[i - 1][j + 1], dp[i - 1][j] - prices[i]);
                dp[i][j + 2] = Math.max(dp[i - 1][j + 2], dp[i - 1][j + 1] + prices[i]);
            }
        }
        return dp[len - 1][k*2];
    }
}