https://leetcode.com/problems/best-time-to-buy-and-sell-stock/
class Solution { public: int maxProfit(vector<int>& prices) { if (prices.size()<2) return 0; int minv=prices[0]; int profit=0; for (int i=0;i<prices.size();i++) { if (prices[i]<minv) { minv=prices[i]; } if ((prices[i]-minv)>profit) { profit=(prices[i]-minv); } } return profit; } };