69 lines
3.7 KiB
Markdown
69 lines
3.7 KiB
Markdown
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# 2020 Day 7: Handy Haversacks
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Copyright (c) Eric Wastl
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#### [Direct Link](https://adventofcode.com/2020/day/7)
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## Part 1
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You land at the regional airport in time for your next flight. In fact, it looks like you'll even have time to grab some food: all flights are currently delayed due to **issues in luggage processing**.
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Due to recent aviation regulations, many rules (your puzzle input) are being enforced about bags and their contents; bags must be color-coded and must contain specific quantities of other color-coded bags. Apparently, nobody responsible for these regulations considered how long they would take to enforce!
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For example, consider the following rules:
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```
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light red bags contain 1 bright white bag, 2 muted yellow bags.
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dark orange bags contain 3 bright white bags, 4 muted yellow bags.
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bright white bags contain 1 shiny gold bag.
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muted yellow bags contain 2 shiny gold bags, 9 faded blue bags.
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shiny gold bags contain 1 dark olive bag, 2 vibrant plum bags.
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dark olive bags contain 3 faded blue bags, 4 dotted black bags.
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vibrant plum bags contain 5 faded blue bags, 6 dotted black bags.
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faded blue bags contain no other bags.
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dotted black bags contain no other bags.
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```
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These rules specify the required contents for 9 bag types. In this example, every `faded blue bag` is empty, every `vibrant plum bag` contains 11 bags (5 `faded blue` and 6 `dotted black`), and so on.
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You have a **`shiny gold`** bag. If you wanted to carry it in at least one other bag, how many different bag colors would be valid for the outermost bag? (In other words: how many colors can, eventually, contain at least one `shiny gold` bag?)
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In the above rules, the following options would be available to you:
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- A `bright white bag`, which can hold your `shiny gold` bag directly.
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- A `muted yellow bag`, which can hold your shiny `gold bag` directly, plus some other bags.
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- A `dark orange bag`, which can hold `bright white` and `muted yellow` bags, either of which could then hold your `shiny gold` bag.
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- A `light red bag`, which can hold `bright white` and `muted yellow` bags, either of which could then hold your `shiny gold` bag.
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So, in this example, the number of bag colors that can eventually contain at least one `shiny gold` bag is **`4`**.
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**How many bag colors can eventually contain at least one `shiny gold` bag?** (The list of rules is quite long; make sure you get all of it.)
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## Part 2
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It's getting pretty expensive to fly these days - not because of ticket prices, but because of the ridiculous number of bags you need to buy!
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Consider again your `shiny gold` bag and the rules from the above example:
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- `faded blue` bags contain `0` other bags.
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- `dotted black` bags contain `0` other bags.
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- `vibrant plum` bags contain `11` other bags: `5` faded blue bags and `6` dotted black bags.
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- `dark olive` bags contain `7` other bags: `3` faded blue bags and `4` dotted black bags.
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So, a single shiny gold bag must contain 1 `dark olive` bag (and the 7 bags within it) plus 2 `vibrant plum` bags (and the 11 bags within **each** of those): `1 + 1*7 + 2 + 2*11` = **`32`** bags!
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Of course, the actual rules have a small chance of going several levels deeper than this example; be sure to count all of the bags, even if the nesting becomes topologically impractical!
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Here's another example:
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```
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shiny gold bags contain 2 dark red bags.
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dark red bags contain 2 dark orange bags.
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dark orange bags contain 2 dark yellow bags.
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dark yellow bags contain 2 dark green bags.
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dark green bags contain 2 dark blue bags.
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dark blue bags contain 2 dark violet bags.
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dark violet bags contain no other bags.
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```
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In this example, a single `shiny gold` bag must contain **`126`** other bags.
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**How many individual bags are required inside your single `shiny gold` bag?**
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