advent-of-code-2025/csharp/adventOfCode/day8/Main.cs

namespace adventOfCode.day8;

internal record Point(long X, long Y, long Z)
{
    public static Point Parse(string line)
    {
        var tmp = line.Split(",");
        return new Point(int.Parse(tmp[0]), int.Parse(tmp[1]), int.Parse(tmp[2]));
    }

    public long Dist(Point p)
    {
        return (p.X - X) * (p.X - X) + (p.Y - Y) * (p.Y - Y) + (p.Z - Z) * (p.Z - Z);
    }
}

internal record PointPairs(Point P1, Point P2) : IComparable<PointPairs>
{
    public int CompareTo(PointPairs other)
    {
        return Dist().CompareTo(other.Dist());
    }

    private long Dist()
    {
        return P1.Dist(P2);
    }
}

internal class Circuit : IComparable<Circuit>
{
    private readonly ISet<Point> points;

    public Circuit()
    {
        points = new HashSet<Point>();
    }

    public int CompareTo(Circuit other)
    {
        return Count().CompareTo(other.Count());
    }

    public bool IsLinkedTo(Point point)
    {
        return points.Contains(point);
    }

    public void Add(Point point)
    {
        points.Add(point);
    }

    public int Count()
    {
        return points.Count();
    }

    public bool IsLinkedTo(PointPairs pointPairs)
    {
        return IsLinkedTo(pointPairs.P1) || IsLinkedTo(pointPairs.P2);
    }

    public void Add(PointPairs pointPairs)
    {
        Add(pointPairs.P1);
        Add(pointPairs.P2);
    }

    public override string ToString()
    {
        var ret = "";
        foreach (var p in points) ret += $"({p.X}, {p.Y}, {p.Z}), ";

        return ret;
    }

    public void AddAll(Circuit circuit)
    {
        foreach (var point in circuit.points) points.Add(point);
    }
}

internal class Circuits
{
    private readonly List<Circuit> circuits;

    public Circuits()
    {
        circuits = new List<Circuit>();
    }

    public void Add(PointPairs pointPairs)
    {
        var addedCircuits = new List<Circuit>();
        foreach (var circuit in circuits)
            if (circuit.IsLinkedTo(pointPairs))
            {
                circuit.Add(pointPairs);
                addedCircuits.Add(circuit);
            }

        if (addedCircuits.Count == 1) return;

        if (addedCircuits.Count < 1)
        {
            var newCircuit = new Circuit();
            newCircuit.Add(pointPairs);
            circuits.Add(newCircuit);
            return;
        }

        var mergedCircuit = new Circuit();
        foreach (var circuit in addedCircuits)
        {
            mergedCircuit.AddAll(circuit);
            circuits.Remove(circuit);
        }

        circuits.Add(mergedCircuit);
    }

    public List<Circuit> Get()
    {
        circuits.Sort();
        circuits.Reverse();
        return circuits;
    }

    public int Count()
    {

        return circuits.Count;
    }
}

public class Question
{
    private static List<Point> parseInput(string input)
    {
        var lines = input.Split("\n");
        var ret = new List<Point>();
        foreach (var line in lines) ret.Add(Point.Parse(line));
        return ret;
    }

    private static List<PointPairs> CreateAllPointPairs(List<Point> points)
    {
        var ret = new List<PointPairs>();
        for (var i = 0; i < points.Count; i++)
        {
            var p = points[i];
            for (var j = i + 1; j < points.Count; j++) ret.Add(new PointPairs(p, points[j]));
        }

        ret.Sort();
        return ret;
    }

    private static Circuits CreateCircuits(List<PointPairs> twoPointsList, int n)
    {
        var circuits = new Circuits();
        var i = 0;
        foreach (var twoPoints in twoPointsList)
        {
            if (i >= n) break;
            circuits.Add(twoPoints);
            i++;
        }

        return circuits;
    }
    
    private static PointPairs? CreateOnBigCircuit(List<PointPairs> twoPointsList, int total)
    {
        var circuits = new Circuits();
        foreach (var twoPoints in twoPointsList)
        {
            circuits.Add(twoPoints);
            if (circuits.Count() == 1 && circuits.Get()[0].Count() == total)
            {
                return twoPoints;
            }
        }

        return null;
    }

    static long Question8A(string document, int n)
    {
        var points = parseInput(document);
        var twoPoints = CreateAllPointPairs(points);
        var circuits = CreateCircuits(twoPoints, n).Get();

        return circuits[0].Count() * circuits[1].Count() * circuits[2].Count();
    }
    
    static long Question8B(string document)
    {
        var points = parseInput(document);
        var twoPoints = CreateAllPointPairs(points);
        var circuits = CreateOnBigCircuit(twoPoints, points.Count);
        if (circuits == null)
        {
            return 0;
        }

        return circuits.P1.X * circuits.P2.X;
    }

    public static void Main()
    {
        Console.WriteLine($"The answer to question 8a is {Question8A(Inputs.Input, 1_000)}" );
        Console.WriteLine($"The answer to question 8b is {Question8B(Inputs.Input)}" );
        
    }
}