You find yourself standing on a snow-covered coastline; apparently, you landed a little off course. The region is too hilly to see the North Pole from here, but you do spot some Elves that seem to be trying to unpack something that washed ashore. It's quite cold out, so you decide to risk creating a paradox by asking them for directions.

"Oh, are you the search party?" Somehow, you can understand whatever Elves from the year 1018 speak; you assume it's Ancient Nordic Elvish. Could the device on your wrist also be a translator? "Those clothes don't look very warm; take this." They hand you a heavy coat.

Read the full puzzle.

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

namespace AdventOfCode.Y2018.Day07;

[ProblemName("The Sum of Its Parts")]
class Solution : Solver {

    public object PartOne(string input) {

        var sb = new StringBuilder();
        var graph = Parse(input);
        while (graph.Any()) {
            char minKey = char.MaxValue;
            foreach (var key in graph.Keys) {
                if (graph[key].Count == 0) {
                    if (key < minKey) {
                        minKey = key;
                    }
                }
            }
            sb.Append(minKey);
            graph.Remove(minKey);
            foreach (var key in graph.Keys) {
                graph[key].Remove(minKey);
            }
        }
        return sb.ToString();
    }

    public object PartTwo(string input) {
        var time = 0;
        var graph = Parse(input);

        var works = new int[5];
        var items = new char[works.Length];

        while (graph.Any() || works.Any(work => work > 0)) {
            for (var i = 0; i < works.Length && graph.Any(); i++) {
                // start working
                if (works[i] == 0) {
                    char minKey = char.MaxValue;
                    foreach (var key in graph.Keys) {
                        if (graph[key].Count == 0) {
                            if (key < minKey) {
                                minKey = key;
                            }
                        }
                    }
                    if (minKey != char.MaxValue) {
                        works[i] = 60 + minKey - 'A' + 1;
                        items[i] = minKey;
                        graph.Remove(items[i]);
                    }
                }
            }

            time++;

            for (var i = 0; i < works.Length; i++) {
                if (works[i] == 0) {
                    // wait
                    continue;
                } else if (works[i] == 1) {
                    // finish
                    works[i]--;
                    foreach (var key in graph.Keys) {
                        graph[key].Remove(items[i]);
                    }

                } else if (works[i] > 0) {
                    // step
                    works[i]--;
                }
            }
        }

        return time;
    }

    Dictionary<char, List<char>> Parse(string input) {
        var dict = (
            from line in input.Split("\n")
            let parts = line.Split(" ")
            let part = parts[7][0]
            let partDependsOn = parts[1][0]
            group partDependsOn by part into g
            select g
        ).ToDictionary(g => g.Key, g => g.ToList());

        foreach (var key in new List<char>(dict.Keys)) {
            foreach (var d in dict[key]) {
                if (!dict.ContainsKey(d)) {
                    dict.Add(d, new List<char>());
                }
            }
        }
        return dict;
    }
}

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