面试经典 150 题 （九）

动态规划，五种状态，关键是找出状态转移式

class Solution {
    public int maxProfit(int[] prices) {
        
        int buy1 = -prices[0];
        int sell1 = 0;
        int buy2 = -prices[0];
        int sell2 = 0;
        for(int i = 1;i < prices.length; i++){
            buy1 = Math.max(buy1, - prices[i]);
            sell1 = Math.max(sell1, buy1 + prices[i]);
            buy2 = Math.max(buy2, sell1 - prices[i]);
            sell2 = Math.max(sell2, buy2 + prices[i]);
        }
        return sell2;
    }
}