def read_file():
	with open("input.txt","r") as f:
		return f.read().split('\n')

def find_row(rowpart):
	row = [*range(128)] # create a list using unpack operator
	for c in rowpart:
		if c == 'F':
			row = row[:len(row)//2] # lower half
		elif c == 'B':
			row = row[len(row)//2:] # upper half
		else:
			break
	return row[0] # extract from list

def find_col(colpart):
	col = [*range(8)] # create a list using unpack operator
	for c in colpart:
		if c == 'L':
			col = col[:len(col)//2] # lower half
		elif c == 'R':
			col = col[len(col)//2:] # upper half
		else:
			break
	return col[0] # extract from list

def id(seat):
	rowpart = seat[:-3]
	colpart = seat[7:]
	row = find_row(rowpart)
	col = find_col(colpart)
	return 8*row + col

def part1(seats):
	max_id = 0
	for seat in seats:
		if id(seat) > max_id:
			max_id = id(seat)
	return max_id

def part2(seats):
	your_seat = 0
	ids = sorted(map(id, seats))
	prev_id = 0
	for seat_id in ids:
		if seat_id - prev_id == 2: # gap detected
			return seat_id - 1 # so your seat is the one right before
		prev_id = seat_id

def main():
	seats = read_file()
	print(f'{part1(seats)=}')
	print(f'{part2(seats)=}')

if __name__ == "__main__":
	main()