121. Best Time to Buy and Sell Stock

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

You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.

Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.

• new solution update 2022.02.07

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int res = 0, st = INT_MAX;
        for(auto& n : prices) {
            st = min(st, n);
            res = max(res , n - st);
        }
        return res;
    }
};

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int res = 0, price = 0;
        for(int i = prices.size() - 1; i >= 0; i--) {
            res = max(res, price - prices[i]);
            price = max(price, prices[i]);
        }

        return res;
    }
};