/*

First, I wanna know how much money I could have made yesterday if I'd been trading Apple stocks all day.

​

So I grabbed Apple's stock prices from yesterday and put them in an array called stockPrices, where:

​

The indices are the time (in minutes) past trade opening time, which was 9:30am local time.

The values are the price (in US dollars) of one share of Apple stock at that time.

So if the stock cost $500 at 10:30am, that means stockPrices[60] = 500.

​

Write a method that takes stockPrices and returns the best profit I could have made from one purchase and one sale of one share of Apple stock yesterday.

​

For example:

​

  var stockPrices = new List<int> { 10, 7, 5, 8, 11, 9 };

​

// Returns 6 (buying for $5 and selling for $11)

GetMaxProfit(stockPrices);

​

No "shorting"—you need to buy before you can sell. Also, you can't buy and sell in the same time step—at least 1 minute has to pass.

*/

​

using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var allTests = new List<(List<int>, int)>

        { 

            (new List<int> { 10, 7, 5, 8, 11, 9 }, 6),

            (new List<int> { 10, 9, 11, 5, 8, 9 }, 4),

            (new List<int> { 12, 11, 10, 9, 7, 6 }, -1),

            (new List<int> { 10, 6, 11, 5, 8, 9 }, 5),

            (new List<int> { 12, 10, 8, 6, 4, 2 }, -2),

            (new List<int> { 2, 8, 1, 6, 3, 5 }, 6),

            (new List<int> { 12, 6, 11, 5, 8, 9 }, 5),

        };

        foreach (var (stockPrices, expected) in allTests)

        {

            Console.WriteLine($"Found Max profit: {GetMaxProfit(stockPrices)}  Expected: {expected}");

        }

    }

    public static int GetMaxProfit(IReadOnlyList<int> stockPrices)

    {

        if (stockPrices.Count < 2)

        {

            return 0;

        }

        var min = stockPrices[0];

        int? profit = null;

        for (int i = 1; i < stockPrices.Count; ++i)

        {

            var temp = stockPrices[i] - min;

            if (min > stockPrices[i])

            {

                min = stockPrices[i];

            }

            if (profit is null || temp > profit)

            {

                profit = temp;

            }

        }

        return profit.Value;

    }

}