You land at the regional airport in time for your next flight. In fact, it looks like you'll even have time to grab some food: all flights are currently delayed due to issues in luggage processing.

Due to recent aviation regulations, many rules (your puzzle input) are being enforced about bags and their contents; bags must be color-coded and must contain specific quantities of other color-coded bags. Apparently, nobody responsible for these regulations considered how long they would take to enforce!

Read the full puzzle.

using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace AdventOfCode.Y2020.Day07;

[ProblemName("Handy Haversacks")]
class Solution : Solver {

    public object PartOne(string input) {
        var parentsOf = new Dictionary<string, HashSet<string>>();
        foreach (var line in input.Split("\n")) {
            var descr = ParseLine(line);

            foreach (var (_, bag) in descr.children) {
                if (!parentsOf.ContainsKey(bag)) {
                    parentsOf[bag] = new HashSet<string>();
                }
                parentsOf[bag].Add(descr.bag);
            }
        }

        IEnumerable<string> PathsToRoot(string bag) {
            yield return bag;

            if (parentsOf.ContainsKey(bag)) {
                foreach (var container in parentsOf[bag]) {
                    foreach (var bagT in PathsToRoot(container)) {
                        yield return bagT;
                    }
                }
            }
        }

        return PathsToRoot("shiny gold bag").ToHashSet().Count - 1;
    }

    public object PartTwo(string input) {
        var childrenOf = new Dictionary<string, List<(int count, string bag)>>();
        foreach (var line in input.Split("\n")) {
            var descr = ParseLine(line);
            childrenOf[descr.bag] = descr.children;
        }

        long CountWithChildren(string bag) =>
            1 + (from child in childrenOf[bag] select child.count * CountWithChildren(child.bag)).Sum();

        return CountWithChildren("shiny gold bag") - 1;
    }

    (string bag, List<(int count, string bag)> children) ParseLine(string line){
        var bag = Regex.Match(line, "^[a-z]+ [a-z]+ bag").Value;

        var children =
            Regex
                .Matches(line, "(\\d+) ([a-z]+ [a-z]+ bag)")
                .Select(x => (count: int.Parse(x.Groups[1].Value), bag: x.Groups[2].Value))
                .ToList();
        
        return (bag, children);
    }

}

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