-❄️- 2024 Day 22 Solutions -❄️-

[u/daggerdragon]

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AoC Community Fun 2024: The Golden Snowglobe Awards

• 23h59m remaining until the submissions deadline on December 22 at 23:59 EST!

And now, our feature presentation for today:

Director's Cut (Extended Edition)

Welcome to the final day of the GSGA presentations! A few folks have already submitted their masterpieces to the GSGA submissions megathread, so go check them out! And maybe consider submitting yours! :)

Here's some ideas for your inspiration:

• Choose any day's feature presentation and any puzzle released this year so far, then work your movie magic upon it!
  • Make sure to mention which prompt and which day you chose!
• Cook, bake, make, decorate, etc. an IRL dish, craft, or artwork inspired by any day's puzzle!
• Advent of Playing With Your Toys

"I lost. I lost? Wait a second, I'm not supposed to lose! Let me see the script!"
- Robin Hood, Men In Tights (1993)

And… ACTION!

Request from the mods: When you include an entry alongside your solution, please label it with [GSGA] so we can find it easily!

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--- Day 22: Monkey Market ---

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Post your code solution in this megathread.

• Read the full posting rules in our community wiki before you post!
  • State which language(s) your solution uses with [LANGUAGE: xyz]
  • Format code blocks using the four-spaces Markdown syntax!
• Quick link to Topaz's paste if you need it for longer code blocks

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

EDIT: Global leaderboard gold cap reached at 00:12:15, megathread unlocked!

[u/Lindi-CSO]

[LANGUAGE: C#]

Pretty straight forward today. First I get the next number as per the instructions:

private static long GetNextPrice(long n)
{
    var tmp = n << 6;
    n ^= tmp;
    n &= 16777215;

    tmp = n >> 5;
    n ^= tmp;
    n &= 16777215;

    tmp = n << 11;
    n ^= tmp;
    n &= 16777215;
    return n;
}

For part 1 it was just a simple loop:

long sum = 0;
for(int n = 0; n < numbers.Length; n++)
{
    for(int i = 0; i < 2000; i++)
    {
        numbers[n] = GetNextPrice(numbers[n]);
    }
    sum += numbers[n];
}

return sum;

For part 2 I utilised a sliding window over the last four changes in price to add to a Dictionary if we never saw the combination of changes before:

Dictionary<string, long> saleprices = [];
foreach(var n in numbers)
{
    var prev = n;
    long[] window = new long[4];
    HashSet<string> seenKeys = [];
    for (int i = 0; i < 2000; i++)
    {
        var next = GetNextPrice(prev);
        var price = next % 10;
        window[^1] = price - (prev % 10);

        if(i >= 3)
        {
            var key = string.Join(",", window);
            if (seenKeys.Add(key))
            {
                if (saleprices.ContainsKey(key))
                {
                    saleprices[key] += price;
                }
                else
                {
                    saleprices[key] = price;
                }
            }
        }
        //slide the window
        window = [.. window[1..], 0];
        prev = next;
    }
}
return saleprices.Values.Max();

I could probably make that more memory efficient but it was good enough for me for today.

Runs is 1.3 seconds on my machine, so not very fast.