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Day 4

Giant Squid

view the Advent of Code 2021 Day 4 challenge

Setup

# Setup - load any packages
from copy import deepcopy

Load the data

# load the data
day4_raw = open('day4_data.txt').read().splitlines()

# extract the numbers called from the first item in the list
# pop extracts and removes them from the input
numbers_called = day4_raw.pop(0).split(',')

#extract the next row as it is blank
day4_raw.pop(0)

def create_bingo_cards(cards):
    # card count
    count = 1
    # dictionary to hold all bingo cards
    bingo_cards = {}
    #temporary list to hold a single bingo card
    bingo_card = []

    #for each row in the data
    for row in cards:
        # check for empty line signalling the start/end of a card
        if row =='':
            # add the current card to the dictionary
            bingo_cards['card_'+str(count)] = bingo_card
            # reset the temporary bingo card
            bingo_card = []
            # increase card count
            count = count + 1
        else:
            # append the row to the current card
            bingo_card.append(row.split())
    # return the dictionary of cards
    return bingo_cards

# make the bingo cards
bingo_cards = create_bingo_cards(day4_raw)

Part 1

def call_numbers(bingo_cards, numbers_called, part_one=True):
    # create a temp copy of the bingo cards so we can update them
    # Using deepcopy as the dictioanry contains other objects
    bingo_cards_temp = deepcopy(bingo_cards)
    # create a dictioanry to store the winning cards
    winners = {}

    # loop through the numbers called
    for num in numbers_called:
        #update each card to mark off the numbers called
        for card, rows in bingo_cards_temp.items():
            #only update cards that haven't yet won
            if card not in winners:
                # itterate through each row in the card
                for idx, row in enumerate(rows):
                    # check if number called is in the row
                    if num in row:
                        #number is in the row so repalce with x
                        row[row.index(num)] = 'x'
                        # update the row in the card
                        bingo_cards_temp[card][idx] = row

                        # Check if the card is a winner
                        if check_winner(bingo_cards_temp[card]):         
                            if part_one: 
                                #The first card has won, calculate the answer and return it
                                return calculate(int(num), bingo_cards_temp[card])
                            
                            # Add the winning card to the winners dictionary
                            winners[card] = calculate(int(num),bingo_cards_temp[card])
                            
    # Return the result of the calculation for the last card in the winners dictionary
    return winners[list(winners.keys())[-1]]

def check_winner(card):
    # copy the card using depcopy so we can alter it to make checking easier
    card_temp=deepcopy(card)
    # transpose the columns into rows
    columns=list(map(list, zip(*card)))
    # append the transposed columns as rows
    for sublist in columns:
        card_temp.append(sublist)
    # check each row
    for row in card_temp:
        if gotaline(row):
            # winning line found
            return True
        
def gotaline(row):
    # is the number of x's the same as the number of items
    # Return a boolean list of number =='x'
    # All function returns True if all items are True
    return all([num=='x' for num in row])

def calculate(num, card):
    # sum the numbers that are not X
    unmarked_sum = sum([int(x) for y in card for x in y if x != 'x'])
    # multiply the sum by the last number called and return it
    return unmarked_sum*num

# calculate part 1 answer
p1_answer = call_numbers(bingo_cards, numbers_called)
print(f'answer = {p1_answer}')

answer = 51776

Part 2

view the Advent of Code 2021 Day 4 challenge Part 2

# calculate part 2 answer
p2_answer = call_numbers(bingo_cards, numbers_called, False)
print(f'answer = {p2_answer}')

answer = 16830