309. Best Time to Buy and Sell Stock with Cooldown

题目

Say you have an array for which the ith element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and sell one share of the stock multiple times) with the following restrictions:

You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).
After you sell your stock, you cannot buy stock on next day. (ie, cooldown 1 day)
Example:

prices = [1, 2, 3, 0, 2]
maxProfit = 3
transactions = [buy, sell, cooldown, buy, sell]

---

思路

用dp做，搞三个数组sell，buy，reset做买卖，cooldown的记录当前的最大收益，遍历求最大值

---

代码

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        if(prices.size() < 1)
        {
            return 0;
        }
        //reset
        vector<int> s0(prices.size(),0);
        //buy
        vector<int> s1(prices.size(),0);
        //sell
        vector<int> s2(prices.size(),0);

        s0[0] = 0;
        s1[0] = -prices[0];
        s2[0] = INT_MIN;

        for(int i=1;i < prices.size();i++)
        {
            s0[i] = max(s0[i-1],s2[i-1]);
            s1[i] = max(s1[i-1],s0[i-1]-prices[i]);
            s2[i] = max(s2[i-1],s1[i-1]+prices[i]);
        }

        return max(s0[prices.size()-1],s2[prices.size()-1]);
    }
};