LeetCode309. 最佳买卖股票时机含冷冻期

class Solution {
    public int maxProfit(int[] prices) {
        if (prices == null || prices.length == 0) return 0;
        int len = prices.length;
        
        int[][] dp = new int[len][3];
        // dp[i][j] 到第 i 天结束不同状态的最大收益
        // j = 0 : 未持股且不是冷冻期  j = 1 : 持股   j = 2 : 冷冻期(今天卖出，不持股)
        dp[0][1] = -prices[0];
        for (int i = 1; i < len; i++) {
            dp[i][0] = Math.max(dp[i-1][0], dp[i-1][2]);
            dp[i][1] = Math.max(dp[i-1][1], dp[i-1][0] - prices[i]);
            dp[i][2] = dp[i-1][1] + prices[i];
        }
        return Math.max(dp[len-1][0], dp[len-1][2]);

        // 空间优化
        /*
        int dp0 = 0, dp2 = 0;
        int dp1 = -prices[0];
        for (int i = 1; i < len; i++) {
            int newDp0 = Math.max(dp0, dp2);
            int newDp1 = Math.max(dp1, dp0 - prices[i]);
            int newDp2 = dp1 + prices[i];
            dp0 = newDp0;
            dp1 = newDp1;
            dp2 = newDp2;
        }
        return Math.max(dp0, dp2);
        */
    }
}