aoc_day5_2020.py

def partition(start, end, top):
    if top:
        return start, start + (end - start) // 2
    return start + (end - start) // 2 + 1, end


def score_seat(boarding_pass):
    start_row = 0
    end_row = 127

    for c in boarding_pass[:-3]:
        start_row, end_row = partition(start_row, end_row, c == 'F')

    start_col = 0
    end_col = 7

    for c in boarding_pass[-3:]:
        start_col, end_col = partition(start_col, end_col, c == 'L')

    return start_row * 8 + start_col


# part 1
print(max([score_seat(x) for x in INPUT.split("\n")]))

# part 2
used_seats = set([score_seat(x) for x in INPUT.split("\n")])
seats_remaining = set(range(0, 127 * 7)).symmetric_difference(used_seats)
for score in seats_remaining:
    if score + 1 not in seats_remaining and score - 1 not in seats_remaining:
        print(score)
        break