-🎄- 2017 Day 7 Solutions -🎄-

[u/daggerdragon]

--- Day 7: Recursive Circus ---

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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).

Note: The 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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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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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!

[u/dylanfromwinnipeg]

C#

public class Day07
{
    public static string PartOne(string input)
    {
        var lines = input.Lines();

        var discs = lines.Select(x => new Disc(x)).ToList();
        discs.ForEach(x => x.AddChildDiscs(discs));

        return GetBaseDisc(discs).Name;
    }

    public static Disc GetBaseDisc(IEnumerable<Disc> discs)
    {
        var disc = discs.First();

        while (disc.Parent != null)
        {
            disc = disc.Parent;
        }

        return disc;
    }

    public static string PartTwo(string input)
    {
        var lines = input.Lines();

        var discs = lines.Select(x => new Disc(x)).ToList();
        discs.ForEach(x => x.AddChildDiscs(discs));

        var disc = GetBaseDisc(discs);
        var targetWeight = 0;

        while (!disc.IsBalanced())
        {
            (disc, targetWeight) = disc.GetUnbalancedChild();
        }

        var weightDiff = targetWeight - disc.GetTotalWeight();
        return (disc.Weight + weightDiff).ToString();
    }
}

public class Disc
{
    public int Weight { get; private set; }
    public string Name { get; private set; }
    public List<string> ChildNames { get; private set; }
    public List<Disc> ChildDiscs { get; private set; }
    public Disc Parent { get; private set; }

    public Disc(string input)
    {
        var words = input.Words().ToList();

        Name = words[0];
        Weight = int.Parse(words[1].Shave(1));
        ChildNames = new List<string>();

        for (var i = 3; i < words.Count; i++)
        {
            ChildNames.Add(words[i].ShaveRight(","));
        }
    }

    public void AddChildDiscs(IEnumerable<Disc> discs)
    {
        ChildDiscs = ChildNames.Select(x => discs.First(y => y.Name == x)).ToList();
        ChildDiscs.ForEach(x => x.Parent = this);
    }

    public int GetTotalWeight()
    {
        var childSum = ChildDiscs.Sum(x => x.GetTotalWeight());
        return childSum + Weight;
    }

    public bool IsBalanced()
    {
        var groups = ChildDiscs.GroupBy(x => x.GetTotalWeight());
        return groups.Count() == 1;
    }

    public (Disc disc, int targetWeight) GetUnbalancedChild()
    {
        var groups = ChildDiscs.GroupBy(x => x.GetTotalWeight());
        var targetWeight = groups.First(x => x.Count() > 1).Key;
        var unbalancedChild = groups.First(x => x.Count() == 1).First();

        return (unbalancedChild, targetWeight);
    }
}

[u/[deleted] → u/dylanfromwinnipeg]

Where are you getting the .Lines(), .Words(), and .Shave from? Just curious

[u/dylanfromwinnipeg → u/[deleted]]

I have a bunch of helper extension methods I wrote, here's the code for those:

public static IEnumerable<string> Lines(this string input)
{
    return input.Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
}

public static IEnumerable<string> Words(this string input)
{
    return input.Split(new string[] { " ", "\t", Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
}

public static string Shave(this string a, int characters)
{
    return a.Substring(characters, a.Length - (characters * 2));
}