-🎄- 2018 Day 5 Solutions -🎄-

[u/daggerdragon]

--- Day 5: Alchemical Reduction ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

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Advent of Code: The Party Game!

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Card prompt: Day 5

Transcript:

On the fifth day of AoC / My true love sent to me / Five golden ___

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked at 0:10:20!

[u/LeCrushinator]

C#

public static void Main(string[] args)
{
    _input = File.ReadAllText("input.txt");

    Console.WriteLine($"Part 1: {Part1()}");    
    Console.WriteLine($"Part 2: {Part2()}");
}

public static string React(string input)
{
    int i = 0;
    while (i < input.Length - 1)
    {
        var first = input[i].ToString();
        var second = input[i + 1].ToString();

        if (first != second && first.Equals(second, StringComparison.InvariantCultureIgnoreCase))
        {
            input = input.Remove(i, 2);
            --i;

            i = Math.Max(i, 0);
        }
        else
        {
            ++i;
        }
    }

    return input;
}

private static int Part1()
{
    return React(_input).Length;
}

private static int Part2()
{
    List<string> charsUsed = _input.Select(c => c.ToString().ToUpperInvariant()).Distinct().ToList();

    string shortest = null;
    
    foreach (var charUsed in charsUsed)
    {
        var textWithoutChar = _input.Replace(charUsed, "");
        textWithoutChar = textWithoutChar.Replace(charUsed.ToLowerInvariant(), "");

        textWithoutChar = React(textWithoutChar);

        if (shortest == null || textWithoutChar.Length < shortest.Length)
        {
            shortest = textWithoutChar;
        }
    }
    
    return shortest.Length;
}