309. Best Time to Buy and Sell Stock with Cooldown

题目链接：

dp来解，要用两个dp array分别表示现在的操作是buy还是sell，优化空间用滚动数组，或者几个int

public class Solution {    public int maxProfit(int[] prices) {        if(prices.length == 0) return 0;        /* buy[i] = Math.max(sell[i-2]-prices[i], buy[i-1])         * sell[i] = Math.max(sell[i-1], buy[i-1] + prices[i])         */        int preBuy = Integer.MIN_VALUE, curBuy = Integer.MIN_VALUE;        int preSell = 0, curSell = 0;        for(int price : prices) {            preBuy = curBuy;            curBuy = Math.max(preSell - price, preBuy);            preSell = curSell;            curSell = Math.max(preSell, preBuy + price);        }                return curSell;    }}