Project-AOC-2024/Day4/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];
}

Console.WriteLine($"Part1: {FindXmas(charArray)}\nPart2: {FindMas(charArray)}");

int FindMas(char[,] grid)
{
    var rows = grid.GetLength(0);
    var cols = grid.GetLength(1);

    var searchDirections = new[,]
    {
        { -1, 1 }, // diagonal up right
        { 1, 1 }, // diagonal down right
        { -1, -1 }, // diagonal up left
        { 1, -1 } // diagonal down left
    };

    List<string> masCenterCoordinates = new();

    for (var row = 0; row < rows; row++)
    {
        for (var column = 0; column < cols; column++)
        {
            for (var direction = 0; direction < searchDirections.GetLength(0); direction++)
            {
                var masCoordinates = CheckWord(row, column, searchDirections[direction, 0], searchDirections[direction, 1], grid, "MAS");
                if (masCoordinates != null)
                {
                    masCenterCoordinates.Add($"{masCoordinates[1][0]},{masCoordinates[1][1]}");
                }
            }
        }
    }

    var masCountDict = masCenterCoordinates.GroupBy(item => item).ToDictionary(group => group.Key, group => group.Count()).Where(x => x.Value > 1);

    return masCountDict.Count();
}

int FindXmas(char[,] grid)
{
    var rows = grid.GetLength(0);
    var cols = grid.GetLength(1);
    var xmasCount = 0;

    var searchDirections = new[,]
    {
        { -1, 0 }, // up
        { 0, 1 }, // right
        { 0, -1 }, // left
        { 1, 0 }, // down
        { -1, 1 }, // diagonal up right
        { 1, 1 }, // diagonal down right
        { -1, -1 }, // diagonal up left
        { 1, -1 } // diagonal down left
    };

    for (var row = 0; row < rows; row++)
    {
        for (var column = 0; column < cols; column++)
        {
            for (var direction = 0; direction < searchDirections.GetLength(0); direction++)
            {
                if (CheckWord(row, column, searchDirections[direction, 0], searchDirections[direction, 1], grid, "XMAS") != null)
                {
                    xmasCount++;
                }
            }
        }
    }

    return xmasCount;
}

List<int[]>? CheckWord(int row, int column, int directionRow, int directionColumn, char[,] grid, string word)
{
    var characterCoordinates = new List<int[]>();

    for (var i = 0; i < word.Length; i++)
    {
        var newRow = row + i * directionRow;
        var newColumn = column + i * directionColumn;
        if (!IsValid(newRow, newColumn, grid) || grid[newRow, newColumn] != word[i]) return null;

        characterCoordinates.Add([newRow, newColumn]);
    }

    return characterCoordinates;
}

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