64 lines
3.0 KiB
Plaintext
64 lines
3.0 KiB
Plaintext
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--- Day 4: Scratchcards ---
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The gondola takes you up. Strangely, though, the ground doesn't seem to be
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coming with you; you're not climbing a mountain. As the circle of Snow Island
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recedes below you, an entire new landmass suddenly appears above you! The
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gondola carries you to the surface of the new island and lurches into the
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station.
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As you exit the gondola, the first thing you notice is that the air here is much
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warmer than it was on Snow Island. It's also quite humid. Is this where the
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water source is?
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The next thing you notice is an Elf sitting on the floor across the station in
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what seems to be a pile of colorful square cards.
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"Oh! Hello!" The Elf excitedly runs over to you. "How may I be of service?" You
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ask about water sources.
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"I'm not sure; I just operate the gondola lift. That does sound like something
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we'd have, though - this is Island Island, after all! I bet the gardener would
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know. He's on a different island, though - er, the small kind surrounded by
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water, not the floating kind. We really need to come up with a better naming
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scheme. Tell you what: if you can help me with something quick, I'll let you
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borrow my boat and you can go visit the gardener. I got all these scratchcards
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as a gift, but I can't figure out what I've won."
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The Elf leads you over to the pile of colorful cards. There, you discover dozens
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of scratchcards, all with their opaque covering already scratched off. Picking
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one up, it looks like each card has two lists of numbers separated by a vertical
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bar (|): a list of winning numbers and then a list of numbers you have. You
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organize the information into a table (your puzzle input).
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As far as the Elf has been able to figure out, you have to figure out which of
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the numbers you have appear in the list of winning numbers. The first match
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makes the card worth one point and each match after the first doubles the point
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value of that card.
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For example:
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Card 1: 41 48 83 86 17 | 83 86 6 31 17 9 48 53
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Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
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Card 3: 1 21 53 59 44 | 69 82 63 72 16 21 14 1
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Card 4: 41 92 73 84 69 | 59 84 76 51 58 5 54 83
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Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
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Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11
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In the above example, card 1 has five winning numbers (41, 48, 83, 86, and 17)
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and eight numbers you have (83, 86, 6, 31, 17, 9, 48, and 53). Of the numbers
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you have, four of them (48, 83, 17, and 86) are winning numbers! That means card
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1 is worth 8 points (1 for the first match, then doubled three times for each of
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the three matches after the first).
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Card 2 has two winning numbers (32 and 61), so it is worth 2 points.
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Card 3 has two winning numbers (1 and 21), so it is worth 2 points.
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Card 4 has one winning number (84), so it is worth 1 point.
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Card 5 has no winning numbers, so it is worth no points.
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Card 6 has no winning numbers, so it is worth no points.
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So, in this example, the Elf's pile of scratchcards is worth 13 points.
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Take a seat in the large pile of colorful cards. How many points are they worth
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in total?
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