Solution to problem 4 in Python

src/Year_2023/Day04.py

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+# --- Day 4: Scratchcards ---
+
+# The gondola takes you up. Strangely, though, the ground doesn't seem to be
+# coming with you; you're not climbing a mountain. As the circle of Snow Island
+# recedes below you, an entire new landmass suddenly appears above you! The
+# gondola carries you to the surface of the new island and lurches into the
+# station.
+
+# As you exit the gondola, the first thing you notice is that the air here is
+# much warmer than it was on Snow Island. It's also quite humid. Is this where
+# the water source is?
+
+# The next thing you notice is an Elf sitting on the floor across the station in
+# what seems to be a pile of colorful square cards.
+
+# "Oh! Hello!" The Elf excitedly runs over to you. "How may I be of service?"
+# You ask about water sources.
+
+# "I'm not sure; I just operate the gondola lift. That does sound like something
+# we'd have, though - this is Island Island, after all! I bet the gardener would
+# know. He's on a different island, though - er, the small kind surrounded by
+# water, not the floating kind. We really need to come up with a better naming
+# scheme. Tell you what: if you can help me with something quick, I'll let you
+# borrow my boat and you can go visit the gardener. I got all these scratchcards
+# as a gift, but I can't figure out what I've won."
+
+# The Elf leads you over to the pile of colorful cards. There, you discover
+# dozens of scratchcards, all with their opaque covering already scratched off.
+# Picking one up, it looks like each card has two lists of numbers separated by
+# a vertical bar (|): a list of winning numbers and then a list of numbers you
+# have. You organize the information into a table (your puzzle input).
+
+# As far as the Elf has been able to figure out, you have to figure out which of
+# the numbers you have appear in the list of winning numbers. The first match
+# makes the card worth one point and each match after the first doubles the
+# point value of that card.
+
+# For example:
+
+# Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+# Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+# Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+# Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+# Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+# Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11
+
+# In the above example, card 1 has five winning numbers (41, 48, 83, 86, and 17)
+# and eight numbers you have (83, 86, 6, 31, 17, 9, 48, and 53). Of the numbers
+# you have, four of them (48, 83, 17, and 86) are winning numbers! That means
+# card 1 is worth 8 points (1 for the first match, then doubled three times for
+# each of the three matches after the first).
+
+#     Card 2 has two winning numbers (32 and 61), so it is worth 2 points.
+#     Card 3 has two winning numbers (1 and 21), so it is worth 2 points.
+#     Card 4 has one winning number (84), so it is worth 1 point.
+#     Card 5 has no winning numbers, so it is worth no points.
+#     Card 6 has no winning numbers, so it is worth no points.
+
+# So, in this example, the Elf's pile of scratchcards is worth 13 points.
+
+# Take a seat in the large pile of colorful cards. How many points are they worth in total?
+
+with open("files/P4.txt") as f:
+    cards = [line for line in f.read().strip().split("\n")]
+
+
+def part1():
+    total = 0
+    for card in cards:
+        game = card.split(":")[1].split("|")
+        winning = set(int(n) for n in game[0].split())
+        hand = set(int(n) for n in game[1].split())
+
+        winners = list(winning & hand)
+
+        if (winning_hand := len(winners)) == 1:
+            total += 1
+        if winning_hand > 1:
+            total += pow(2, winning_hand - 1)
+
+    print(f"There are {total} points in total")
+
+
+# --- Part Two ---
+
+# Just as you're about to report your findings to the Elf, one of you realizes
+# that the rules have actually been printed on the back of every card this whole
+# time.
+
+# There's no such thing as "points". Instead, scratchcards only cause you to win
+# more scratchcards equal to the number of winning numbers you have.
+
+# Specifically, you win copies of the scratchcards below the winning card equal
+# to the number of matches. So, if card 10 were to have 5 matching numbers, you
+# would win one copy each of cards 11, 12, 13, 14, and 15.
+
+# Copies of scratchcards are scored like normal scratchcards and have the same
+# card number as the card they copied. So, if you win a copy of card 10 and it
+# has 5 matching numbers, it would then win a copy of the same cards that the
+# original card 10 won: cards 11, 12, 13, 14, and 15. This process repeats until
+# none of the copies cause you to win any more cards. (Cards will never make you
+# copy a card past the end of the table.)
+
+# This time, the above example goes differently:
+
+# Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+# Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+# Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+# Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+# Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+# Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11
+
+#     Card 1 has four matching numbers, so you win one copy each of the next
+# four cards: cards 2, 3, 4, and 5.
+#     Your original card 2 has two matching numbers, so you win one copy each of
+# cards 3 and 4.
+#     Your copy of card 2 also wins one copy each of cards 3 and 4.
+#     Your four instances of card 3 (one original and three copies) have two
+# matching numbers, so you win four copies each of cards 4 and 5.
+#     Your eight instances of card 4 (one original and seven copies) have one
+# matching number, so you win eight copies of card 5.
+#     Your fourteen instances of card 5 (one original and thirteen copies) have
+# no matching numbers and win no more cards.
+#     Your one instance of card 6 (one original) has no matching numbers and
+# wins no more cards.
+
+# Once all of the originals and copies have been processed, you end up with 1
+# instance of card 1, 2 instances of card 2, 4 instances of card 3, 8 instances
+# of card 4, 14 instances of card 5, and 1 instance of card 6. In total, this
+# example pile of scratchcards causes you to ultimately have 30 scratchcards!
+
+# Process all of the original and copied scratchcards until no more scratchcards
+# are won. Including the original set of scratchcards, how many total
+# scratchcards do you end up with?
+
+
+from collections import defaultdict
+
+score = defaultdict(int)
+
+
+def part2():
+    for idx, card in enumerate(cards):
+        game = card.split(":")[1].split("|")
+        winning = set(int(n) for n in game[0].split())
+        hand = set(int(n) for n in game[1].split())
+
+        winners = list(winning & hand)
+
+        score[idx] += 1
+        for i, _ in enumerate(winners):
+            score[idx + 1 + i] += score[idx]
+
+    print(f"There are {sum(score.values())} scratchcards")
+
+
+if __name__ == "__main__":
+    part1()
+    part2()