129 lines
4.6 KiB
Python
129 lines
4.6 KiB
Python
# --- Day 5: Binary Boarding ---
|
|
|
|
# You board your plane only to discover a new problem: you dropped your
|
|
# boarding pass! You aren't sure which seat is yours, and all of the flight
|
|
# attendants are busy with the flood of people that suddenly made it through
|
|
# passport control.
|
|
|
|
# You write a quick program to use your phone's camera to scan all of the
|
|
# nearby boarding passes (your puzzle input); perhaps you can find your seat
|
|
# through process of elimination.
|
|
|
|
# Instead of zones or groups, this airline uses binary space partitioning to
|
|
# seat people. A seat might be specified like FBFBBFFRLR, where F means
|
|
# "front", B means "back", L means "left", and R means "right".
|
|
|
|
# The first 7 characters will either be F or B; these specify exactly one of
|
|
# the 128 rows on the plane (numbered 0 through 127). Each letter tells you
|
|
# which half of a region the given seat is in. Start with the whole list of
|
|
# rows; the first letter indicates whether the seat is in the front (0 through
|
|
# 63) or the back (64 through 127). The next letter indicates which half of
|
|
# that region the seat is in, and so on until you're left with exactly one row.
|
|
|
|
# For example, consider just the first seven characters of FBFBBFFRLR:
|
|
|
|
# Start by considering the whole range, rows 0 through 127.
|
|
# F means to take the lower half, keeping rows 0 through 63.
|
|
# B means to take the upper half, keeping rows 32 through 63.
|
|
# F means to take the lower half, keeping rows 32 through 47.
|
|
# B means to take the upper half, keeping rows 40 through 47.
|
|
# B keeps rows 44 through 47.
|
|
# F keeps rows 44 through 45.
|
|
# The final F keeps the lower of the two, row 44.
|
|
|
|
# The last three characters will be either L or R; these specify exactly one of
|
|
# the 8 columns of seats on the plane (numbered 0 through 7). The same process
|
|
# as above proceeds again, this time with only three steps. L means to keep the
|
|
# lower half, while R means to keep the upper half.
|
|
|
|
# For example, consider just the last 3 characters of FBFBBFFRLR:
|
|
|
|
# Start by considering the whole range, columns 0 through 7.
|
|
# R means to take the upper half, keeping columns 4 through 7.
|
|
# L means to take the lower half, keeping columns 4 through 5.
|
|
# The final R keeps the upper of the two, column 5.
|
|
|
|
# So, decoding FBFBBFFRLR reveals that it is the seat at row 44, column 5.
|
|
|
|
# Every seat also has a unique seat ID: multiply the row by 8, then add the
|
|
# column. In this example, the seat has ID 44 * 8 + 5 = 357.
|
|
|
|
# Here are some other boarding passes:
|
|
|
|
# BFFFBBFRRR: row 70, column 7, seat ID 567.
|
|
# FFFBBBFRRR: row 14, column 7, seat ID 119.
|
|
# BBFFBBFRLL: row 102, column 4, seat ID 820.
|
|
|
|
# As a sanity check, look through your list of boarding passes. What is the
|
|
# highest seat ID on a boarding pass?
|
|
|
|
with open("files/P5.txt", "r") as f:
|
|
boarding_passes = [code for code in f.read().strip().split("\n")]
|
|
|
|
|
|
def binary_search(
|
|
arr: str, upper_limit: int, var_lower: str, var_upper: str
|
|
) -> int:
|
|
range_l = 0
|
|
range_h = upper_limit
|
|
range_m = 0
|
|
for char in arr:
|
|
range_m = (range_h + range_l) // 2
|
|
if char == var_lower:
|
|
range_h = range_m
|
|
elif char == var_upper:
|
|
range_l = range_m + 1
|
|
return int(range_l)
|
|
|
|
|
|
def part_1() -> None:
|
|
seat_ID: int = 0
|
|
for code in boarding_passes:
|
|
row, col = code[:7], code[-3:]
|
|
|
|
_row = binary_search(row, 127, "F", "B")
|
|
_col = binary_search(col, 7, "L", "R")
|
|
_seat_ID: int = _row * 8 + _col
|
|
seat_ID = max(seat_ID, _seat_ID)
|
|
|
|
print(f"The highest seat ID on a boarding pass is {seat_ID}")
|
|
|
|
|
|
# --- Part Two ---
|
|
|
|
# Ding! The "fasten seat belt" signs have turned on. Time to find your seat.
|
|
|
|
# It's a completely full flight, so your seat should be the only missing
|
|
# boarding pass in your list. However, there's a catch: some of the seats at
|
|
# the very front and back of the plane don't exist on this aircraft, so they'll
|
|
# be missing from your list as well.
|
|
|
|
# Your seat wasn't at the very front or back, though; the seats with IDs +1 and
|
|
# -1 from yours will be in your list.
|
|
|
|
# What is the ID of your seat?
|
|
|
|
|
|
def part_2() -> None:
|
|
seat_IDs: list[int] = []
|
|
missing_seats: list[int] = []
|
|
for code in boarding_passes:
|
|
row, col = code[:7], code[-3:]
|
|
|
|
_row = binary_search(row, 127, "F", "B")
|
|
_col = binary_search(col, 7, "L", "R")
|
|
_seat_ID: int = _row * 8 + _col
|
|
seat_IDs.append(_seat_ID)
|
|
|
|
for ID in range(len(boarding_passes)):
|
|
if ID in seat_IDs:
|
|
pass
|
|
else:
|
|
missing_seats.append(ID)
|
|
print(f"The ID of my seat is {missing_seats[-1]}")
|
|
|
|
|
|
if __name__ == "__main__":
|
|
part_1()
|
|
part_2()
|