doc/day07.html

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      <h1 class="title-global"><a href="https://adventofcode.com/2020" target="_blank">Advent of Code</a></h1>
      <div class="user">John Dugan</div>
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      <h1 class="title-event">&nbsp;&nbsp;<span class="title-event-wrap">{year=&gt;</span><a href="https://adventofcode.com/2020" target="_blank">2020</a><span class="title-event-wrap">}</span></h1>
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    <article class="day-desc">
      <h2>--- Day 7: Handy Haversacks ---</h2>
      <p>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 <em>issues in luggage processing</em>.</p>
      <p>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!</p>
      <p>For example, consider the following rules:</p>
      <pre><code>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.
</code></pre>
      <p>These rules specify the required contents for 9 bag types. In this example, every <code>faded blue</code> bag is empty, every <code>vibrant plum</code> bag contains 11 bags (5 <code>faded blue</code> and 6 <code>dotted black</code>), and so
        on.</p>
      <p>You have a <code><em>shiny gold</em></code> 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
        <code>shiny gold</code> bag?)</p>
      <p>In the above rules, the following options would be available to you:</p>
      <ul>
        <li>A <code>bright white</code> bag, which can hold your <code>shiny gold</code> bag directly.</li>
        <li>A <code>muted yellow</code> bag, which can hold your <code>shiny gold</code> bag directly, plus some other bags.</li>
        <li>A <code>dark orange</code> bag, which can hold <code>bright white</code> and <code>muted yellow</code> bags, either of which could then hold your <code>shiny gold</code> bag.</li>
        <li>A <code>light red</code> bag, which can hold <code>bright white</code> and <code>muted yellow</code> bags, either of which could then hold your <code>shiny gold</code> bag.</li>
      </ul>
      <p>So, in this example, the number of bag colors that can eventually contain at least one <code>shiny gold</code> bag is <code><em>4</em></code>.</p>
      <p><em>How many bag colors can eventually contain at least one <code>shiny gold</code> bag?</em> (The list of rules is quite long; make sure you get all of it.)</p>
    </article>
    <p>Your puzzle answer was <code>257</code>.</p>
    <article class="day-desc">
      <h2 id="part2">--- Part Two ---</h2>
      <p>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!</p>
      <p>Consider again your <code>shiny gold</code> bag and the rules from the above example:</p>
      <ul>
        <li><code>faded blue</code> bags contain <code>0</code> other bags.</li>
        <li><code>dotted black</code> bags contain <code>0</code> other bags.</li>
        <li><code>vibrant plum</code> bags contain <code>11</code> other bags: 5 <code>faded blue</code> bags and 6 <code>dotted black</code> bags.</li>
        <li><code>dark olive</code> bags contain <code>7</code> other bags: 3 <code>faded blue</code> bags and 4 <code>dotted black</code> bags.</li>
      </ul>
      <p>So, a single <code>shiny gold</code> bag must contain 1 <code>dark olive</code> bag (and the 7 bags within it) plus 2 <code>vibrant plum</code> bags (and the 11 bags within <em>each</em> of those): <code>1 + 1*7 + 2 + 2*11</code> = <code><em>32</em></code>
        bags!</p>
      <p>Of course, the actual rules have a <span title="100%">small</span> chance of going several levels deeper than this example; be sure to count all of the bags, even if the nesting becomes topologically impractical!</p>
      <p>Here's another example:</p>
      <pre><code>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.
</code></pre>
      <p>In this example, a single <code>shiny gold</code> bag must contain <code><em>126</em></code> other bags.</p>
      <p><em>How many individual bags are required inside your single <code>shiny gold</code> bag?</em></p>
    </article>
    <p>Your puzzle answer was <code>1038</code>.</p>
    <p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
    <p>At this point, you should <a href="index.html">return to your Advent calendar</a> and try another puzzle.</p>
    <p>If you still want to see it, you can <a href="../data/day07/input.txt" target="_blank">get your puzzle input</a>.</p>
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