problem_121.java

/*
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. */

class Solution {
    public int maxProfit(int[] prices) {
        int minPrice = Integer.MAX_VALUE;
        int maxProfit = 0;
        for (int price : prices) {
            if (price < minPrice) {
                minPrice = price;   
            } else {
                int profit = price - minPrice;
                if (profit > maxProfit) {
                    maxProfit = profit;
                }
            }
        }
        return maxProfit;
    }
}