57 lines
3.1 KiB
Markdown
57 lines
3.1 KiB
Markdown
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# Day 4: Scratchcards
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## Part 1
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The gondola takes you up. Strangely, though, the ground doesn't seem to be coming with you; you're not climbing a
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mountain. As the circle of Snow Island recedes below you, an entire new landmass suddenly appears above you!
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The gondola carries you to the surface of the new island and lurches into the station.
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As you exit the gondola, the first thing you notice is that the air here is much **warmer** than it was on Snow Island.
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It's also quite **humid**. Is this where the water source is?
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The next thing you notice is an Elf sitting on the floor across the station in what seems to be a pile of colorful
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square cards.
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"Oh! Hello!" The Elf excitedly runs over to you. "How may I be of service?" You ask about water sources.
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"I'm not sure; I just operate the gondola lift. That does sound like something we'd have, though - this is
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**Island Island**, after all! I bet the **gardener** would know. He's on a different island, though - er, the small
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kind surrounded by water, not the floating kind. We really need to come up with a better naming scheme. Tell you what:
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if you can help me with something quick, I'll let you **borrow my boat** and you can go visit the gardener.
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I got all these scratchcards 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 of scratchcards, all with their opaque
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covering already scratched off. Picking 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 organize the information into a table
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(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 the **numbers you have** appear in the
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list of winning numbers. The first match makes the card worth **one point** and each match after the first **doubles**
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the point value of that card.
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For example:
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```
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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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```
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In the above example, card 1 has five winning numbers (`41`, `48`, `83`, `86`, and `17`) and eight numbers you have
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(`83`, `86`, `6`, `31`, `17`, `9`, `48`, and `53`). Of the numbers you have, four of them (`48`, `83`, `17`, and `86`)
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are winning numbers! That means card 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 in total?**
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