Advent of Code 2023 - Day 11

var input = File.ReadAllLines("input.txt");

var startingGalaxies = new List<(int Row, int Column)>();
var emptyRows = new List<int>();

for (var row = 0; row < input.Length; row++)
{
    var line = input[row];
    if (!line.Contains('#'))
    {
        emptyRows.Add(row);
    }

    for (var col = 0; col < line.Length; col++)
    {
        var c = line[col];
        if (c == '#')
        {
            startingGalaxies.Add((row, col));
        }
    }
}

var emptyCols = new List<int>();
for (var col = 0; col < input[0].Length; col++)
{
    if (startingGalaxies.All(g => g.Column != col))
    {
        emptyCols.Add(col);
    }
}

Console.WriteLine($"Part 1: {CalculateDistances()}");
Console.WriteLine($"Part 2: {CalculateDistances(1_000_000)}");
return;

long CalculateDistances(int factor = 2)
{
    var galaxies = new List<(int Row, int Column)>(startingGalaxies);

    foreach (var emptyRow in emptyRows)
    {
        for (var i = 0; i < startingGalaxies.Count; i++)
        {
            if (startingGalaxies[i].Row > emptyRow)
            {
                galaxies[i] = (galaxies[i].Row + factor - 1, galaxies[i].Column);
            }
        }
    }

    foreach (var emptyCol in emptyCols)
    {
        for (var i = 0; i < startingGalaxies.Count; i++)
        {
            if (startingGalaxies[i].Column > emptyCol)
            {
                galaxies[i] = (galaxies[i].Row, galaxies[i].Column + factor - 1);
            }
        }
    }

    var result = 0L;

    for (var i = 0; i < galaxies.Count - 1; i++)
    {
        for (var j = i + 1; j < galaxies.Count; j++)
        {
            result += Math.Abs(galaxies[j].Row - galaxies[i].Row) + Math.Abs(galaxies[j].Column - galaxies[i].Column);
        }
    }

    return result;
}