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04.worksheet.sc
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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?
--- 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?
*/