You are given an integer array prices where prices[i] is the price of a given stock on the ith day.

On each day, you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However, you can buy it then immediately sell it on the same day.

Find and return the maximum profit you can achieve.

class Solution {
public:
int maxProfit(vector& prices) {
//经典动态规划
//如何表示当天进行的交易
// 注意一点为啥是这个顺序
int a_i0=0; //无股票
int a_i1=INT_MIN; //有股票
for(auto pp:prices){
a_i0=max(a_i0,a_i1+pp);
a_i1=max(a_i1,a_i0-pp);
}
return a_i0;

}  

};