advent-2024-04.cs

var lines = new List<string>();

using var reader = new StreamReader(args[0]);
while (reader.ReadLine() is string line)
{
    lines.Add(line);
}

var grid = new char[lines.Count, lines[0].Length];
for (var i = 0; i < lines.Count; i++)
{
    for (var j = 0; j < lines[i].Length; j++)
    {
        grid[i, j] = lines[i][j];
    }
}

lines.Clear();

int xmas = 0;

for (int i = 0; i < grid.GetLength(0); i++)
{
    for (int j = 0; j < grid.GetLength(1); j++)
    {
        if (i < grid.GetLength(0) - 2 && j < grid.GetLength(1) - 2)
        {
            xmas += ((grid[i + 0, j], grid[i + 0, j + 1], grid[i + 0, j + 2]),
                     (grid[i + 1, j], grid[i + 1, j + 1], grid[i + 1, j + 2]),
                     (grid[i + 2, j], grid[i + 2, j + 1], grid[i + 2, j + 2])) switch
            {
                (('M', _, 'S'),
                 (_, 'A', _),
                 ('M', _, 'S')) => 1,
                (('S', _, 'M'),
                 (_, 'A', _),
                 ('S', _, 'M')) => 1,
                (('M', _, 'M'),
                 (_, 'A', _),
                 ('S', _, 'S')) => 1,
                (('S', _, 'S'),
                 (_, 'A', _),
                 ('M', _, 'M')) => 1,
                _ => 0
            };
        }
    }
}

Console.WriteLine(xmas);