AdventOfCode/AdventOfCode.Solutions/2023/Day 11/Day11.cs

using System.Text.RegularExpressions;

namespace AdventOfCode.Solutions._2023
{
    public class Day11 : IChallange
    {
        public int Year => 2023;
        public int Day => 11;

        private readonly InputReader _inputReader;

        public Day11(InputReader inputReader)
        {
            _inputReader = inputReader;
            _inputReader.SetInput(this);
        }

        public async Task<string> GetSolutionPart1()
        {
            string[] data = await _inputReader.ReadAsArrayString();
            return CreateUniverseAndGetDistances(data).ToString();
        }

        public async Task<string> GetSolutionPart2()
        {
            string[] data = await _inputReader.ReadAsArrayString();
            return CreateUniverseAndGetDistances(data, true).ToString();
        }

        private long CreateUniverseAndGetDistances(string[] lineInput, bool part2 = false)
        {
            List<int> columns = []; // the list of indexes where expation takes place
            for (int columnIndex = 0;  columnIndex < lineInput[0].Length; columnIndex++) 
            {
                if(lineInput.Select(line => line[columnIndex]).All(c => c == '.'))
                {
                    columns.Add(columnIndex);
                }
            }

            List<Galaxy> galaxies = [];
            int rowsAdded = 0; // the rows where expation takes place
            for (int rowIndex = 0;  rowIndex < lineInput.Length; rowIndex++) 
            { 
                if (lineInput[rowIndex].All(c => c == '.'))
                {
                    rowsAdded++; // add and continue
                    continue;
                }

                foreach (Match galaxyMatch in Regex.Matches(lineInput[rowIndex], @"#"))
                {
                    int columnExpantion = columns.Where(c => c < galaxyMatch.Index).Count();
                    Galaxy newGalaxy = new(rowIndex, galaxyMatch.Index, columnExpantion, rowsAdded);
                    galaxies.Add(newGalaxy);
                }
            }

            long total = 0;

            for (int galaxiesIndex = 0; galaxiesIndex < galaxies.Count - 1; galaxiesIndex++)
            {
                total += galaxies
                    .Where(g => galaxies.IndexOf(g) > galaxiesIndex) // only take the next ones, skip all prev ones
                    .Select(g => 
                        galaxies[galaxiesIndex].GetManhattanDistance(g) + // get the distance
                        galaxies[galaxiesIndex].GetExpantionsDistance(g, part2) // get the expantion distance
                    )
                    .Sum();
            }

            return total;
        }

        private class Galaxy(int x, int y, int xExpantion, int yExpantion) : Node(x, y, '#')
        {
            public int HorizonalExpantions { get; set; } = xExpantion;
            public int VerticalExpantions { get; set; } = yExpantion;

            public long GetExpantionsDistance(Galaxy other, bool part2 = false)
            {
                int times = Math.Abs(HorizonalExpantions - other.HorizonalExpantions) + Math.Abs(VerticalExpantions - other.VerticalExpantions);
                
                if (part2)
                {
                    return (times * 1_000_000) - times;
                }

                return times;
            }
        }
    }
}