public static void Solve()
{
const string PuzzleInput = ".^^.^^^..^.^..^.^^.^^^^.^^.^^...^..^...^^^..^^...^..^^^^^^..^.^^^..^.^^^^.^^^.^...^^^.^^.^^^.^.^^.^.";
const bool Part2 = true;
const bool Safe = true; // false => Trap
const int Rows = Part2 ? 400000 : 40;
bool[][] tiles = new bool[Rows][];
int safeTiles = 0;
tiles[0] = PuzzleInput.ToCharArray().Select(c => c == '.').ToArray();
safeTiles = tiles[0].Count(c => c == Safe);
int cols = tiles[0].Length;
for (int row = 1; row < Rows; row++)
{
tiles[row] = new bool[cols];
for (int col = 0; col < cols; col++)
{
bool leftSafe = col == 0 ? true : tiles[row - 1][col - 1];
bool centerSafe = tiles[row - 1][col];
bool rightSafe = col == (cols - 1) ? true : tiles[row - 1][col + 1];
bool isTrap =
(!leftSafe && !centerSafe && rightSafe) ||
(leftSafe && !centerSafe && !rightSafe) ||
(!leftSafe && centerSafe && rightSafe) ||
(leftSafe && centerSafe && !rightSafe);
tiles[row][col] = !isTrap;
safeTiles += (isTrap ? 0 : 1);
}
}
Console.WriteLine(safeTiles);
}