Advent of Code - 2025 - Day 8

var input = await File.ReadAllLinesAsync("input.txt");

var junctionBoxes = input
    .Select(line => line.Split(','))
    .Select(parts => new JunctionBox(long.Parse(parts[0]), long.Parse(parts[1]), long.Parse(parts[2])))
    .ToList();

var distances = new List<(JunctionBox From, JunctionBox To, long Distance)>();

for (var i = 0; i < junctionBoxes.Count - 1; i++)
{
    var boxA = junctionBoxes[i];

    for (var j = i + 1; j < junctionBoxes.Count; j++)
    {
        var boxB = junctionBoxes[j];
        distances.Add((boxA, boxB, boxA.DistanceTo(boxB)));
    }
}

distances = [.. distances.OrderBy(d => d.Distance)];

var circuits = new List<HashSet<JunctionBox>>();

foreach (var box in junctionBoxes)
{
    circuits.Add([box]);
}

var iteration = 0;

while (true)
{
    iteration++;

    var (from, to, _) = distances[iteration - 1];
    var circuitA = circuits.First(c => c.Contains(from));
    var circuitB = circuits.First(c => c.Contains(to));

    if (circuitA != circuitB)
    {
        circuitA.UnionWith(circuitB);
        circuits.Remove(circuitB);
        circuits = [.. circuits.OrderByDescending(c => c.Count)];
    }

    if (iteration == 1000)
    {
        Console.WriteLine($"Part 1: {circuits[0].Count * circuits[1].Count * circuits[2].Count}");
    }

    if (circuits.All(c => c.Count > 1))
    {
        Console.WriteLine($"Part 2: {from.X * to.X}");
        break;
    }
}

record struct JunctionBox(long X, long Y, long Z)
{
    public readonly long DistanceTo(JunctionBox other) =>
        (long)Math.Sqrt(Math.Pow(X - other.X, 2) + Math.Pow(Y - other.Y, 2) + Math.Pow(Z - other.Z, 2));
}