111 lines
6.1 KiB
Markdown
111 lines
6.1 KiB
Markdown
# Day 7: Camel Cards
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## Part 1
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Your all-expenses-paid trip turns out to be a one-way, five-minute ride in an airship. (At least it's a **cool**
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airship!) It drops you off at the edge of a vast desert and descends back to Island Island.
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"Did you bring the parts?"
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You turn around to see an Elf completely covered in white clothing, wearing goggles, and riding a large camel.
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"Did you bring the parts?" she asks again, louder this time. You aren't sure what parts she's looking for; you're
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here to figure out why the sand stopped.
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"The parts! For the sand, yes! Come with me; I will show you." She beckons you onto the camel.
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After riding a bit across the sands of Desert Island, you can see what look like very large rocks covering half of the
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horizon. The Elf explains that the rocks are all along the part of Desert Island that is directly above Island Island,
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making it hard to even get there. Normally, they use big machines to move the rocks and filter the sand, but the
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machines have broken down because Desert Island recently stopped receiving the **parts** they need to fix the machines.
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You've already assumed it'll be your job to figure out why the parts stopped when she asks if you can help.
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You agree automatically.
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Because the journey will take a few days, she offers to teach you the game of **Camel Cards**. Camel Cards is sort of
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similar to poker except it's designed to be easier to play while riding a camel.
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In Camel Cards, you get a list of **hands**, and your goal is to order them based on the strength of each hand.
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A hand consists of five cards labeled one of `A`, `K`, `Q`, `J`, `T`, `9`, `8`, `7`, `6`, `5`, `4`, `3`, or `2`.
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The relative strength of each card follows this order, where `A` is the highest and `2` is the lowest.
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Every hand is exactly one type. From strongest to weakest, they are:
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- **Five of a kind**, where all five cards have the same label: `AAAAA`
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- **Four of a kind**, where four cards have the same label and one card has a different label: `AA8AA`
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- **Full house**, where three cards have the same label, and the remaining two cards share a different label: `23332`
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- **Three of a kind**, where three cards have the same label, and the remaining two cards are each different from any other card in the hand: `TTT98`
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- **Two pair**, where two cards share one label, two other cards share a second label, and the remaining card has a third label: `23432`
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- **One pair**, where two cards share one label, and the other three cards have a different label from the pair and each other: `A23A4`
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- **High card**, where all cards' labels are distinct: `23456`
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Hands are primarily ordered based on type; for example, every **full house** is stronger than any **three of a kind**.
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If two hands have the same type, a second ordering rule takes effect. Start by comparing the **first card in each hand**.
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If these cards are different, the hand with the stronger first card is considered stronger. If the first card in each
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hand have the **same label**, however, then move on to considering the second card in each hand. If they differ,
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the hand with the higher second card wins; otherwise, continue with the third card in each hand, then the fourth,
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then the fifth.
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So, `33332` and `2AAAA` are both four of a kind hands, but `33332` is stronger because its first card is stronger.
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Similarly, `77888` and `77788` are both a full house, but `77888` is stronger because its third card is stronger
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(and both hands have the same first and second card).
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To play Camel Cards, you are given a list of hands and their corresponding bid (your puzzle input). For example:
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```
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32T3K 765
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T55J5 684
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KK677 28
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KTJJT 220
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QQQJA 483
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```
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This example shows five hands; each hand is followed by its **bid** amount. Each hand wins an amount equal to its bid
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multiplied by its **rank**, where the weakest hand gets rank 1, the second-weakest hand gets rank 2, and so on up to
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the strongest hand. Because there are five hands in this example, the strongest hand will have rank 5 and its bid will
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be multiplied by 5.
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So, the first step is to put the hands in order of strength:
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- `32T3K` is the only **one pair** and the other hands are all a stronger type, so it gets rank **1**.
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- `KK677` and `KTJJT` are both **two pair**. Their first cards both have the same label, but the second card of `KK677` is stronger (K vs T), so `KTJJT` gets rank **2** and `KK677` gets rank **3**.
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- `T55J5` and `QQQJA` are both three of a kind. `QQQJA` has a stronger first card, so it gets rank **5** and `T55J5` gets rank **4**.
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Now, you can determine the total winnings of this set of hands by adding up the result of multiplying each hand's bid
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with its rank (765 * 1 + 220 * 2 + 28 * 3 + 684 * 4 + 483 * 5). So the total winnings in this example are 6440.
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Find the rank of every hand in your set. **What are the total winnings?**
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## Part Two
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To make things a little more interesting, the Elf introduces one additional rule. Now, `J` cards are jokers -
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wildcards that can act like whatever card would make the hand the strongest type possible.
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To balance this, `J` **cards are now the weakest** individual cards, weaker even than `2`. The other cards stay in the
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same order: `A`, `K`, `Q`, `T`, `9`, `8`, `7`, `6`, `5`, `4`, `3`, `2`, `J`.
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J cards can pretend to be whatever card is best for the purpose of determining hand type; for example, `QJJQ2`
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is now considered **four of a kind**. However, for the purpose of breaking ties between two hands of the same type,
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`J` is always treated as `J`, not the card it's pretending to be: `JKKK2` is weaker than `QQQQ2` because J is weaker
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than Q.
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Now, the above example goes very differently:
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```
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32T3K 765
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T55J5 684
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KK677 28
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KTJJT 220
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QQQJA 483
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```
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- `32T3K` is still the only one pair; it doesn't contain any jokers, so its strength doesn't increase.
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- `KK677` is now the only two pair, making it the second-weakest hand.
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- `T55J5`, `KTJJT`, and `QQQJA` are now all four of a kind! `T55J5` gets rank 3, `QQQJA` gets rank 4, and `KTJJT` gets rank 5.
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With the new joker rule, the total winnings in this example are `5905`.
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Using the new joker rule, find the rank of every hand in your set. **What are the new total winnings?**
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