121. Best Time to Buy and Sell Stock.

Problem :

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.

Example 1:

Input: prices = [7,1,5,3,6,4]
Output: 5
Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
Example 2:

Input: prices = [7,6,4,3,1]
Output: 0
Explanation: In this case, no transactions are done and the max profit = 0.

Solution :

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int price = prices[0];
        int profit = 0;
        for(int i=1; i< prices.size(); i++)
        {
            if(price > prices[i])
                price = prices[i];
            else if((prices[i] - price) > profit)
                    profit = prices[i] - price;
        }
        return profit;
    }
};