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 <= 10^5
0 <= prices[i] <= 10^4

Java Solution

class Solution {
    public int maxProfit(int[] prices) {
        int lsf = Integer.MAX_VALUE;
        int op = 0;
        int pist = 0;
        for(int i =0; i<prices.length; i++){
            if(prices[i] < lsf){
                lsf = prices[i];
            }
            pist = prices[i] - lsf;
            if(op < pist){
                op = pist;
            }
        }
        return op;
    }
}