BestTimeToBuyAndSellStock121.php

<?php

declare(strict_types=1);

namespace Fathom\Leetcode\Easy;

/*
https://leetcode.com/problems/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.
 */

class BestTimeToBuyAndSellStock121
{
    public static function maxProfit(array $prices): int
    {
        $profit = 0;
        $buy = PHP_INT_MAX;

        foreach ($prices as $price) {
            $buy = min($buy, $price);
            $profit = max($profit, $price - $buy);
        }

        return $profit;
    }
}