AoC 2021 Day 4: His Name Oh

Source: Giant Squid

Part 1: Given a set of bingo boards and a list of numbers, find the first board to win. Multiply the sum of the un-called numbers on that board times the last number called.

This one was kind of neat! First time that I’m going to break out a few helper functions. First, something to read in the data in the specified format:

• The first line contains a comma-delimited list of numbers in the order they will be called followed by an empty line
• Subsequent lines consist of a 5x5 grid of space delimited numbers (bingo cards) followed by a new line

BingoBoard = List[List[Optional[str]]]

def parse(file: typer.FileText) -> Tuple[List[Int], BingoBoard]:
'''Parse a bingo definition. Return the list of numbers (as ints) and a list of 5x5 grids.'''

numbers = [int(el) for el in file.readline().split(',')]

boards = []
board = []

for line in file:
if not line.strip():
continue

board.append([int(el) for el in line.split()])

if len(board) == 5:
boards.append(board)
board = []

return numbers, boards


This time, we’re using the typer.FileText as an actual file object where we can read off the first line (for numbers), the empty line, and then starting the iteration to read five lines at a time (skipping empty lines). Straight forward enough.

Next, we’re going to write a helper that can take a Bingo board and a number and cross off that number (by marking it as None):

def check_off(board: BingoBoard, number: int):
'''Remove the given number from the given board by changing it to None.'''

# Yes, I know I'm hardcoding 5
for i in range(5):
for j in range(5):
if board[i][j] == number:
board[i][j] = None


No problems, because BingoBoard is defined to to be Optional[int], either int or None.

Next up, check if a Bingo board is solved. I’m particularly proud of this monster:

def is_solved(board):
'''Return True if any row or column is completely None.'''

# This is silly looking
return (
any(
all(board[i][j] is None for j in range(5))
for i in range(5)
) or
any(
all(board[i][j] is None for i in range(5))
for j in range(5)
)
)


As I said. It’s silly looking. Essentially, is any row made of all None in each column or is any column made of all None for each row. I’m curious what ‘cleaner’ ways there would be to write that.

Anyways, once you have all that, the actual ‘solution’ is really short:

def part1(file: typer.FileText):

numbers, boards = parse(file)

for number in numbers:
for board in boards:
check_off(board, number)

# As soon as any board is solved, we're done
if is_solved(board):
remaining_numbers = [el for row in board for el in row if el]
print(f'{remaining_numbers=}, {sum(remaining_numbers)=}, {number=}, product={sum(remaining_numbers)*number}')
return


Part 2: Repeat Part 1, but instead of the first board solved, use the numbers remaining on the last board after it’s solved.

Again, we have the pieces, it’s a matter of turning that into code:

def part2(file: typer.FileText):

numbers, boards = parse(file)

for number in numbers:
for board in boards:
check_off(board, number)

# If (and only if) we're on the last board, check for a solution and bail
if len(boards) == 1 and (board := boards[0]) and is_solved(board):
remaining_numbers = [el for row in board for el in row if el]
print(f'{remaining_numbers=}, {sum(remaining_numbers)=}, {number=}, product={sum(remaining_numbers)*number}')
return

# Otherwise, remove solved boards
boards = [board for board in boards if not is_solved(board)]


Breaking functionality into functions really does make for relative elegant code.

Timing

Still quick, but about twice as slow as previous examples. I expect that I could cut some time out with a more efficient data structure… but it still runs in a fraction of a second.

--- Day 4: Giant Squid ---

$python3 his-name-oh.py part1 input.txt remaining_numbers=[99, 19, 9, 59, 92, 82, 69, 72, 2, 45, 93, 27], sum(remaining_numbers)=668, number=66, product=44088 # time 54675500ns / 0.05s$ python3 his-name-oh.py part2 input.txt
remaining_numbers=[3, 78, 23, 79, 80], sum(remaining_numbers)=263, number=90, product=23670
# time 66984792ns / 0.07s


Type checking

One thing that I’ve been doing is putting type annotations on everything and then (finally) running mypy against it. That’s pretty cool:

\$ mypy his-name-oh.py
Success: no issues found in 1 source file


(I had a few to fix.)