LeetCode Problem #121 : Best time to Buy and Sell Stocks

Question:

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

Initial Solution:

first I iterated over prices and got the max and min prices, then i added the condition to reset when minPrice > p . then I started calculation of profit but the profit was a local one and not the globalmaxima, so then I added maxProfit and made it change when the profit itself changes.

If profit changes, and if the new profit is greater than previously registered maximas then change maxProfit

class Solution {
    public int maxProfit(int[] prices) {
        int profit = 0;
        int minPrice = 100000;
        int maxProfit = 0;
        for(int p : prices) {
            if(minPrice > p) {
                minPrice = p;
                profit = p;
            }
            if(profit < p) {
                profit = p;
                if(maxProfit < profit) maxProfit = profit - minPrice;
            }
        }
        return maxProfit;
    }
}

Peformance: