namespace;
include rt;

// conway's life on a 10 x 20 torus, with typed 2d arrays in a struct.
// a glider walks diagonally and wraps around the edges.
const H = 10, W = 20;
struct board { int[10][20] c; };

int get(board* b, int y, int x) { return b.c[(y + H) % H][(x + W) % W]; }
void step(board* from, board* to) {
	for (int y = 0; y < H; y++)
		for (int x = 0; x < W; x++) {
			int n = 0;
			for (int dy = 0 - 1; dy <= 1; dy++)
				for (int dx = 0 - 1; dx <= 1; dx++)
					if (dy || dx) n += get(from, y + dy, x + dx);
			to.c[y][x] = n == 3 || (n == 2 && from.c[y][x]);
		}
	return;
}
void show(board* b, int gen) {
	rt.put_s("generation "); rt.put_n(gen); rt.put_c(10);
	for (int y = 0; y < H; y++) { for (int x = 0; x < W; x++) rt.put_c(b.c[y][x] ? '#' : '.'); rt.put_c(10); }
	return;
}
void main() {
	board* a = rt.new(board), b = rt.new(board);
	a.c[0][1] = 1; a.c[1][2] = 1; a.c[2][0] = 1; a.c[2][1] = 1; a.c[2][2] = 1;
	// two generations a pass, a -> b -> a: owned boards can't be swapped
	// through a temporary, since the analyzer can't follow that
	for (int g = 0; g <= 40; g += 2) {
		if (g % 20 == 0) show(a, g);
		step(a, b);
		step(b, a);
	}
	rt.free(a); rt.free(b);
	return;
}