AdventOfCode23/Day11/Universe.cs

using System.Collections.ObjectModel;

using Day10;

namespace Day11;

public class Universe
{
    public IList<Galaxy> Galaxies { get; } = new List<Galaxy>();

    public void Add(Galaxy galaxy)
    {
        Galaxies.Add(galaxy);
    }

    public void Expand(int expansionFactor)
    {
        var xMap = new Dictionary<long, IList<Galaxy>>();
        var yMap = new Dictionary<long, IList<Galaxy>>();

        foreach (var g in Galaxies)
        {
            if (!xMap.ContainsKey(g.Position.X))
            {
                xMap.Add(g.Position.X, new List<Galaxy>());
            }
            xMap[g.Position.X].Add(g);
            if (!yMap.ContainsKey(g.Position.Y))
            {
                yMap.Add(g.Position.Y, new List<Galaxy>());
            }
            yMap[g.Position.Y].Add(g);
        }

        var xPrev = -1L;
        var xExpand = 0L;
        foreach (var x in xMap.Keys.Order())
        {
            xExpand += x - xPrev - 1;
            xPrev = x;
            
            foreach (var g in xMap[x])
            {
                var delta = new GridPoint(xExpand * (expansionFactor - 1), 0);
                g.Move(delta);
            }
        }
        
        var yPrev = -1L;
        var yExpand = 0L;
        foreach (var y in yMap.Keys.Order())
        {
            yExpand += y - yPrev - 1;
            yPrev = y;
            
            foreach (var g in yMap[y])
            {
                var delta = new GridPoint(0, yExpand * (expansionFactor - 1));
                g.Move(delta);
            }
        }
    }

    public long GetTotalDistance()
    {
        var sum = 0L;
        foreach (var pair in BuildPairs())
        {
            var distance = pair.Left.Position.Distance(pair.Right.Position);
            Console.WriteLine($"{pair.Left.Id} <-> {pair.Right.Id} = {distance}");
            sum += distance;
        }

        return sum;
    }

    private IEnumerable<(Galaxy Left, Galaxy Right)> BuildPairs()
    {
        for (var i = 0; i < Galaxies.Count - 1; i++)
        {
            for (var j = i + 1; j < Galaxies.Count; j++)
            {
                yield return (Galaxies[i], Galaxies[j]);
            }
        }
    }
}