advent24/Advent24/Day8.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection.Emit;
using System.Text;
using System.Threading.Tasks;
using System.Text.RegularExpressions;

namespace Advent24
{
    internal class Day8
    {
        public Day8()
        {
            String fileData = System.IO.File.ReadAllText(@"..\..\..\inputd8.txt");

            // set this to false for part 1
            Boolean enableResonantHarmonics = true;

            // get width of line to be able to navigate the map block in
            // both dimensions
            Int32 mapWidth = fileData.IndexOf('\n');
            Int32 mapWidthIncludingNewline = mapWidth + 1;
            String pattern = @"[A-Za-z0-9]";

            Regex r = new(pattern, RegexOptions.Multiline, TimeSpan.FromMilliseconds(150));

            Match m = r.Match(fileData);

            // list of linear-integer locations of antennas indexed by antenna type (a single alphanumeric character)
            Dictionary<Char, List<Int32>> antennaLocationsMap = [];

            while (m.Success)
            {
                if (!antennaLocationsMap.TryGetValue(m.Groups[0].Value[0], out List<int>? antennaLocations))
                    antennaLocationsMap.Add(m.Groups[0].Value[0], [m.Groups[0].Index]);
                else
                    antennaLocationsMap[m.Groups[0].Value[0]].Add(m.Groups[0].Index);

                // Console.WriteLine("antennaLocationsMap[{0:d}] = {1:d}", m.Groups[0].Value[0], antennaLocationsMap[m.Groups[0].Value[0]].Last());

                m = m.NextMatch();
            }

            // set of linear-integer locations of antinodes indexed by antenna type (single-character alphanumeric)
            Dictionary<Char, HashSet<Int32>> antinodeLocationsMap = [];

            // set of linear-integer locations of antinodes overall
            HashSet<Int32> overallAntinodeLocations = [];

            foreach (Char antennaType in antennaLocationsMap.Keys)
            {
                if (!antinodeLocationsMap.TryGetValue(antennaType, out HashSet<int>? antinodeLocations))
                    antinodeLocationsMap.Add(antennaType, []);

                // for each (ordered) pair of antennaLocations of the same antenna type, we'll construct an antinode
                // and then add it to the antinodeLocationsMap (keyed by antenna type)
                foreach(Int32 antennaLocation1 in antennaLocationsMap[antennaType])
                    foreach(Int32 antennaLocation2 in antennaLocationsMap[antennaType])
                    {
                        if (antennaLocation1 == antennaLocation2)
                            continue;

                        Int32 antennaLocationDifference = antennaLocation2 - antennaLocation1;
                        Int32 antennaLocationXDifference = (antennaLocation2 % mapWidthIncludingNewline) - (antennaLocation1 % mapWidthIncludingNewline);
                        Int32 antinodeLocation = antennaLocation2;
                        do
                        {
                            Int32 antinodePreviousLocationX = antinodeLocation % mapWidthIncludingNewline; 
                            antinodeLocation += antennaLocationDifference;
                            Int32 antinodeLocationXDifference = (antinodeLocation % mapWidthIncludingNewline) - antinodePreviousLocationX;

                            // bounds checking
                            if (
                                    antinodeLocation < 0 ||
                                    antinodeLocation >= fileData.Length ||
                                    fileData[antinodeLocation] == '\n' ||
                                    // x-direction having changed implies we crossed the right/left boundary
                                    ((antennaLocationXDifference > 0) != (antinodeLocationXDifference > 0))
                               )
                                break;

                            antinodeLocationsMap[antennaType].Add(antinodeLocation);
                        } while (enableResonantHarmonics);

                        if(enableResonantHarmonics)
                        {
                            antinodeLocationsMap[antennaType].Add(antennaLocation1);
                            antinodeLocationsMap[antennaType].Add(antennaLocation2);
                        }
                    }

                // adding to the overall antinode location set
                overallAntinodeLocations = [.. overallAntinodeLocations, .. antinodeLocationsMap[antennaType]];
            }

            Int32 numberOfUniqueAntinodeLocations = overallAntinodeLocations.Count;
            Console.WriteLine("numberOfUniqueAntinodeLocations = {0:d}", numberOfUniqueAntinodeLocations);

            // to keep the console window from closing
            Console.ReadKey();
        }
    }
}