--- /dev/null
+--- Day 7: Handy Haversacks ---
+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.
+
+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!
+
+For example, consider the following rules:
+
+light red bags contain 1 bright white bag, 2 muted yellow bags.
+dark orange bags contain 3 bright white bags, 4 muted yellow bags.
+bright white bags contain 1 shiny gold bag.
+muted yellow bags contain 2 shiny gold bags, 9 faded blue bags.
+shiny gold bags contain 1 dark olive bag, 2 vibrant plum bags.
+dark olive bags contain 3 faded blue bags, 4 dotted black bags.
+vibrant plum bags contain 5 faded blue bags, 6 dotted black bags.
+faded blue bags contain no other bags.
+dotted black bags contain no other bags.
+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.
+
+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?)
+
+In the above rules, the following options would be available to you:
+
+A bright white bag, which can hold your shiny gold bag directly.
+A muted yellow bag, which can hold your shiny gold bag directly, plus some other bags.
+A dark orange bag, which can hold bright white and muted yellow bags, either of which could then hold your shiny gold bag.
+A light red bag, which can hold bright white and muted yellow bags, either of which could then hold your shiny gold bag.
+So, in this example, the number of bag colors that can eventually contain at least one shiny gold bag is 4.
+
+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.)
+
+Your puzzle answer was 197.
+
+--- Part Two ---
+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!
+
+Consider again your shiny gold bag and the rules from the above example:
+
+faded blue bags contain 0 other bags.
+dotted black bags contain 0 other bags.
+vibrant plum bags contain 11 other bags: 5 faded blue bags and 6 dotted black bags.
+dark olive bags contain 7 other bags: 3 faded blue bags and 4 dotted black bags.
+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!
+
+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!
+
+Here's another example:
+
+shiny gold bags contain 2 dark red bags.
+dark red bags contain 2 dark orange bags.
+dark orange bags contain 2 dark yellow bags.
+dark yellow bags contain 2 dark green bags.
+dark green bags contain 2 dark blue bags.
+dark blue bags contain 2 dark violet bags.
+dark violet bags contain no other bags.
+In this example, a single shiny gold bag must contain 126 other bags.
+
+How many individual bags are required inside your single shiny gold bag?
+
+Your puzzle answer was 85324.
+
+Both parts of this puzzle are complete! They provide two gold stars: **
+
+At this point, you should return to your Advent calendar and try another puzzle.
+
+If you still want to see it, you can get your puzzle input.
+
+You can also [Share] this puzzle.
projects / advent-of-code-2020.git / blobdiff