Project-AOC-2024/Day8/Program.cs

var lines = File.ReadAllLines("input.txt");
var charArray = new char[lines.Length, lines[0].Length];

for (var i = 0; i < charArray.GetLength(0); i++)
    for (var j = 0; j < charArray.GetLength(1); j++)
    {
        charArray[i, j] = lines[i][j];
    }

var uniqueCharacterPositions = GroupUniqueCharacterPositions(charArray);

var antinodeLocations = new List<(int, int)>();
var antinodeHarmonicsLocations = new List<(int, int)>();

foreach (var uniqueCharacter in uniqueCharacterPositions)
{
    for (var i = 0; i < uniqueCharacter.Value.Count - 1; i++)
    {
        var currentPosition = uniqueCharacter.Value[i];

        for (var j = i + 1; j < uniqueCharacter.Value.Count; j++)
        {
            var nextPosition = uniqueCharacter.Value[j];

            if (Distance(currentPosition.Item1, currentPosition.Item2, nextPosition.Item1, nextPosition.Item2) >= 1)
            {
                antinodeLocations.AddRange(CalculateAntinodes(currentPosition, nextPosition, charArray));
            }

            antinodeHarmonicsLocations.AddRange(CalculateAntinodesWithHarmonics(currentPosition, nextPosition, charArray));
        }
    }
}

Console.WriteLine(
    $"Part 1: {antinodeLocations.Distinct().Count()}\nPart 2: {antinodeHarmonicsLocations.Distinct().Count()}");

List<(int, int)> CalculateAntinodesWithHarmonics((int, int) currentPosition, (int, int) nextPosition, char[,] input)
{
    var locations = new List<(int, int)>
    {
        currentPosition,
        nextPosition
    };

    var verticalDistance = Math.Abs(currentPosition.Item1 - nextPosition.Item1);
    var horizontalDistance = Math.Abs(currentPosition.Item2 - nextPosition.Item2);

    var currentPositionClone = currentPosition;
    var nextPositionClone = nextPosition;
    int antinodePositionRow, antinodePositionColumn;

    while (true)
    {
        if (currentPositionClone.Item1 < nextPositionClone.Item1)
        {
            antinodePositionRow = currentPositionClone.Item1 - verticalDistance;
        }
        else
        {
            antinodePositionRow = currentPositionClone.Item1 + verticalDistance;
        }

        if (currentPositionClone.Item2 < nextPositionClone.Item2)
        {
            antinodePositionColumn = currentPositionClone.Item2 - horizontalDistance;
        }
        else
        {
            antinodePositionColumn = currentPositionClone.Item2 + horizontalDistance;
        }

        if (IsValid(antinodePositionRow, antinodePositionColumn, input))
        {
            locations.Add((antinodePositionRow, antinodePositionColumn));
            nextPositionClone = currentPositionClone;
            currentPositionClone = (antinodePositionRow, antinodePositionColumn);
        }
        else
        {
            break;
        }
    }

    currentPositionClone = currentPosition;
    nextPositionClone = nextPosition;

    while (true)
    {
        if (currentPositionClone.Item1 < nextPositionClone.Item1)
        {
            antinodePositionRow = nextPositionClone.Item1 + verticalDistance;
        }
        else
        {
            antinodePositionRow = nextPositionClone.Item1 - verticalDistance;
        }

        if (currentPositionClone.Item2 < nextPositionClone.Item2)
        {
            antinodePositionColumn = nextPositionClone.Item2 + horizontalDistance;
        }
        else
        {
            antinodePositionColumn = nextPositionClone.Item2 - horizontalDistance;
        }

        if (IsValid(antinodePositionRow, antinodePositionColumn, input))
        {
            locations.Add((antinodePositionRow, antinodePositionColumn));
            currentPositionClone = nextPositionClone;
            nextPositionClone = (antinodePositionRow, antinodePositionColumn);
        }
        else
        {
            break;
        }
    }

    return locations;
}

List<(int, int)> CalculateAntinodes((int, int) currentPosition, (int, int) nextPosition, char[,] input)
{
    var locations = new List<(int, int)>();

    int firstAntinodePositionRow,
        firstAntinodePositionColumn,
        secondAntinodePositionRow,
        secondAntinodePositionColumn;

    var verticalDistance = Math.Abs(currentPosition.Item1 - nextPosition.Item1);
    var horizontalDistance = Math.Abs(currentPosition.Item2 - nextPosition.Item2);

    if (currentPosition.Item1 < nextPosition.Item1)
    {
        firstAntinodePositionRow = currentPosition.Item1 - verticalDistance;
        secondAntinodePositionRow = nextPosition.Item1 + verticalDistance;
    }
    else
    {
        firstAntinodePositionRow = currentPosition.Item1 + verticalDistance;
        secondAntinodePositionRow = nextPosition.Item1 - verticalDistance;
    }

    if (currentPosition.Item2 < nextPosition.Item2)
    {
        firstAntinodePositionColumn = currentPosition.Item2 - horizontalDistance;
        secondAntinodePositionColumn = nextPosition.Item2 + horizontalDistance;
    }
    else
    {
        firstAntinodePositionColumn = currentPosition.Item2 + horizontalDistance;
        secondAntinodePositionColumn = nextPosition.Item2 - horizontalDistance;
    }

    if (IsValid(firstAntinodePositionRow, firstAntinodePositionColumn, input))
    {
        locations.Add((firstAntinodePositionRow, firstAntinodePositionColumn));
    }

    if (IsValid(secondAntinodePositionRow, secondAntinodePositionColumn, input))
    {
        locations.Add((secondAntinodePositionRow, secondAntinodePositionColumn));
    }

    return locations;
}

Dictionary<char, List<(int, int)>> GroupUniqueCharacterPositions(char[,] array)
{
    var charLocations = new Dictionary<char, List<(int, int)>>();

    for (var i = 0; i < array.GetLength(0); i++)
    {
        for (var j = 0; j < array.GetLength(1); j++)
        {
            var currentChar = array[i, j];

            if (currentChar == '.') continue;

            if (!charLocations.ContainsKey(currentChar))
            {
                charLocations[currentChar] = new List<(int, int)>();
            }

            charLocations[currentChar].Add((i, j));
        }
    }

    return charLocations;
}

bool IsValid(int row, int column, char[,] grid) => row >= 0 && row < grid.GetLength(0) && column >= 0 && column < grid.GetLength(1);

double Distance(int position1Row, int position1Column, int position2Row, int position2Column) =>  Math.Sqrt(Math.Pow(position1Column - position2Column, 2) + Math.Pow(position2Row - position1Row, 2));