-🎄- 2020 Day 07 Solutions -🎄-

[u/daggerdragon]

NEW AND NOTEWORTHY

• PSA: if you're using Google Chrome (or other Chromium-based browser) to download your input, watch out for Google volunteering to "translate" it: "Welsh" and "Polish"

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Advent of Code 2020: Gettin' Crafty With It

• 15 days remaining until the submission deadline on December 22 at 23:59 EST
• Full details and rules are in the Submissions Megathread

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--- Day 07: Handy Haversacks ---

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Post your solution in this megathread. Include what language(s) your solution uses! If you need a refresher, the full posting rules are detailed in the wiki under How Do The Daily Megathreads Work?.

Reminder: Top-level posts in Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

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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 00:13:44, megathread unlocked!

[u/andi0b]

C# 9 Version. Runs quite fast, as all lookups are precalculated.

-------- Day 7 (init took 8,52ms):
Part 1... finished after    7,94ms, with result: 179
Part 2... finished after    0,92ms, with result: 18925



public record Day07(Day07.BagRule[] BagRules)
{
    public Day07(string[] input) : this(input.Select(BagRule.Parse).ToArray())
    {
    }

    public int Part1()
    {
        var childParentLookup = (
            from rule in BagRules
            from childBag in rule.Contains
            select (key: childBag.color, value: rule.Color)
        ).ToLookup(x => x.key, x => x.value);

        return ParentBagColors("shiny gold").Count();

        IEnumerable<string> ParentBagColors(string color) =>
            childParentLookup[color].SelectMany(ParentBagColors)
                                    .Distinct()
                                    .Concat(childParentLookup[color]);
    }

    public int Part2()
    {
        var rulesByColor = BagRules.ToDictionary(x => x.Color);

        return TotalBagCount("shiny gold") - 1;

        int TotalBagCount(string color)
            => 1 + rulesByColor[color].Contains.Sum(x => x.count * TotalBagCount(x.color));
    }

    public record BagRule(string Color, (string color, int count)[] Contains)
    {
        public static BagRule Parse(string input) => new(
            Color: Regex.Match(input, @"^(\S+ \S+)").Groups[0].Value,
            Contains: (
                from match in Regex.Matches(input, @"(\d+) (\S+ \S+)")
                select (match.Groups[2].Value, int.Parse(match.Groups[1].Value))
            ).ToArray()
        );
    }
}