121. Best Time to Buy and Sell Stock | leetcode solution

 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.

 

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.

 

Constraints:

• 1 <= prices.length <= 105
• 0 <= prices[i] <= 104

solution:

class Solution {

public:

    int maxProfit(vector<int>& prices) {

        

        int profit = 0;

        int num = prices[0];

        for(int i = 0 ; i < prices.size(); i++)

        {

            if(num > prices[i] )

                num = prices[i];

            if(prices[i]-num > profit )

                profit = prices[i]-num;

            

        }

        return profit;

        

    }

};