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+<title>Day 24 - Advent of Code 2019</title>
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+Oh, hello! Funny seeing you here.
+
+I appreciate your enthusiasm, but you aren't going to find much down here.
+There certainly aren't clues to any of the puzzles. The best surprises don't
+even appear in the source until you unlock them for real.
+
+Please be careful with automated requests; I'm not a massive company, and I can
+only take so much traffic. Please be considerate so that everyone gets to play.
+
+If you're curious about how Advent of Code works, it's running on some custom
+Perl code. Other than a few integrations (auth, analytics, social media), I
+built the whole thing myself, including the design, animations, prose, and all
+of the puzzles.
+
+The puzzles are most of the work; preparing a new calendar and a new set of
+puzzles each year takes all of my free time for 4-5 months. A lot of effort
+went into building this thing - I hope you're enjoying playing it as much as I
+enjoyed making it for you!
+
+If you'd like to hang out, I'm @ericwastl on Twitter.
+
+- Eric Wastl
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+-->
+<body>
+<header><div><h1 class="title-global"><a href="/">Advent of Code</a></h1><nav><ul><li><a href="/2019/about">[About]</a></li><li><a href="/2019/events">[Events]</a></li><li><a href="https://teespring.com/stores/advent-of-code" target="_blank">[Shop]</a></li><li><a href="/2019/settings">[Settings]</a></li><li><a href="/2019/auth/logout">[Log Out]</a></li></ul></nav><div class="user">Neil Smith <a href="/2019/support" class="supporter-badge" title="Advent of Code Supporter">(AoC++)</a> <span class="star-count">48*</span></div></div><div><h1 class="title-event"> <span class="title-event-wrap">0x0000|</span><a href="/2019">2019</a><span class="title-event-wrap"></span></h1><nav><ul><li><a href="/2019">[Calendar]</a></li><li><a href="/2019/support">[AoC++]</a></li><li><a href="/2019/sponsors">[Sponsors]</a></li><li><a href="/2019/leaderboard">[Leaderboard]</a></li><li><a href="/2019/stats">[Stats]</a></li></ul></nav></div></header>
+
+<div id="sidebar">
+<div id="sponsor"><div class="quiet">Our <a href="/2019/sponsors">sponsors</a> help make Advent of Code possible:</div><div class="sponsor"><a href="https://www.twilio.com/quest" target="_blank" onclick="if(ga)ga('send','event','sponsor','sidebar',this.href);" rel="noopener">TwilioQuest</a> - Play Advent of Code and earn rad loot in TwilioQuest, a developer RPG for Mac, Windows, and Linux. Learn JavaScript, Python, git, APIs for SMS, VoIP, or WhatsApp, and much more.</div></div>
+</div><!--/sidebar-->
+
+<main>
+<script>window.addEventListener('click', function(e,s,r){if(e.target.nodeName==='CODE'&&e.detail===3){s=window.getSelection();s.removeAllRanges();r=document.createRange();r.selectNodeContents(e.target);s.addRange(r);}});</script>
+<article class="day-desc"><h2>--- Day 24: Planet of Discord ---</h2><p>You land on <a href="https://en.wikipedia.org/wiki/Eris_(dwarf_planet)">Eris</a>, your last stop before reaching Santa. As soon as you do, your sensors start picking up strange life forms moving around: Eris is infested with <a href="https://www.nationalgeographic.org/thisday/sep9/worlds-first-computer-bug/">bugs</a>! With an <span title="For a sad version of this story, look up Voices of a Distant Star.">over 24-hour roundtrip</span> for messages between you and Earth, you'll have to deal with this problem on your own.</p>
+<p>Eris isn't a very large place; a scan of the entire area fits into a 5x5 grid (your puzzle input). The scan shows <em>bugs</em> (<code>#</code>) and <em>empty spaces</em> (<code>.</code>).</p>
+<p>Each <em>minute</em>, The bugs live and die based on the number of bugs in the <em>four adjacent tiles</em>:</p>
+<ul>
+<li>A bug <em>dies</em> (becoming an empty space) unless there is <em>exactly one</em> bug adjacent to it.</li>
+<li>An empty space <em>becomes infested</em> with a bug if <em>exactly one or two</em> bugs are adjacent to it.</li>
+</ul>
+<p>Otherwise, a bug or empty space remains the same. (Tiles on the edges of the grid have fewer than four adjacent tiles; the missing tiles count as empty space.) This process happens in every location <em>simultaneously</em>; that is, within the same minute, the number of adjacent bugs is counted for every tile first, and then the tiles are updated.</p>
+<p>Here are the first few minutes of an example scenario:</p>
+<pre><code>Initial state:
+....#
+#..#.
+#..##
+..#..
+#....
+
+After 1 minute:
+#..#.
+####.
+###.#
+##.##
+.##..
+
+After 2 minutes:
+#####
+....#
+....#
+...#.
+#.###
+
+After 3 minutes:
+#....
+####.
+...##
+#.##.
+.##.#
+
+After 4 minutes:
+####.
+....#
+##..#
+.....
+##...
+</code></pre>
+<p>To understand the nature of the bugs, watch for the first time a layout of bugs and empty spaces <em>matches any previous layout</em>. In the example above, the first layout to appear twice is:</p>
+<pre><code>.....
+.....
+.....
+#....
+.#...
+</code></pre>
+<p>To calculate the <em>biodiversity rating</em> for this layout, consider each tile left-to-right in the top row, then left-to-right in the second row, and so on. Each of these tiles is worth biodiversity points equal to <em>increasing powers of two</em>: 1, 2, 4, 8, 16, 32, and so on. Add up the biodiversity points for tiles with bugs; in this example, the 16th tile (<code>32768</code> points) and 22nd tile (<code>2097152</code> points) have bugs, a total biodiversity rating of <code><em>2129920</em></code>.</p>
+<p><em>What is the biodiversity rating for the first layout that appears twice?</em></p>
+</article>
+<p>Your puzzle answer was <code>17863711</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>After careful analysis, one thing is certain: <em>you have no idea where all these bugs are coming from</em>.</p>
+<p>Then, you remember: Eris is an old <a href="20">Plutonian</a> settlement! Clearly, the bugs are coming from recursively-folded space.</p>
+<p>This 5x5 grid is <em>only one</em> level in an <em>infinite</em> number of recursion levels. The tile in the middle of the grid is actually another 5x5 grid, the grid in your scan is contained as the middle tile of a larger 5x5 grid, and so on. Two levels of grids look like this:</p>
+<pre><code> | | | |
+ | | | |
+ | | | |
+-----+-----+---------+-----+-----
+ | | | |
+ | | | |
+ | | | |
+-----+-----+---------+-----+-----
+ | | | | | | | |
+ | |-+-+-+-+-| |
+ | | | | | | | |
+ | |-+-+-+-+-| |
+ | | | |?| | | |
+ | |-+-+-+-+-| |
+ | | | | | | | |
+ | |-+-+-+-+-| |
+ | | | | | | | |
+-----+-----+---------+-----+-----
+ | | | |
+ | | | |
+ | | | |
+-----+-----+---------+-----+-----
+ | | | |
+ | | | |
+ | | | |
+</code></pre>
+<p>(To save space, some of the tiles are not drawn to scale.) Remember, this is only a small part of the infinitely recursive grid; there is a 5x5 grid that contains this diagram, and a 5x5 grid that contains that one, and so on. Also, the <code>?</code> in the diagram contains another 5x5 grid, which itself contains another 5x5 grid, and so on.</p>
+<p>The scan you took (your puzzle input) shows where the bugs are <em>on a single level</em> of this structure. The middle tile of your scan is empty to accommodate the recursive grids within it. Initially, no other levels contain bugs.</p>
+<p>Tiles still count as <em>adjacent</em> if they are directly <em>up, down, left, or right</em> of a given tile. Some tiles have adjacent tiles at a recursion level above or below its own level. For example:</p>
+<pre><code> | | | |
+ 1 | 2 | 3 | 4 | 5
+ | | | |
+-----+-----+---------+-----+-----
+ | | | |
+ 6 | 7 | 8 | 9 | 10
+ | | | |
+-----+-----+---------+-----+-----
+ | |A|B|C|D|E| |
+ | |-+-+-+-+-| |
+ | |F|G|H|I|J| |
+ | |-+-+-+-+-| |
+ 11 | 12 |K|L|?|N|O| 14 | 15
+ | |-+-+-+-+-| |
+ | |P|Q|R|S|T| |
+ | |-+-+-+-+-| |
+ | |U|V|W|X|Y| |
+-----+-----+---------+-----+-----
+ | | | |
+ 16 | 17 | 18 | 19 | 20
+ | | | |
+-----+-----+---------+-----+-----
+ | | | |
+ 21 | 22 | 23 | 24 | 25
+ | | | |
+</code></pre>
+<ul>
+<li>Tile 19 has four adjacent tiles: 14, 18, 20, and 24.</li>
+<li>Tile G has four adjacent tiles: B, F, H, and L.</li>
+<li>Tile D has four adjacent tiles: 8, C, E, and I.</li>
+<li>Tile E has four adjacent tiles: 8, D, 14, and J.</li>
+<li>Tile 14 has <em>eight</em> adjacent tiles: 9, E, J, O, T, Y, 15, and 19.</li>
+<li>Tile N has <em>eight</em> adjacent tiles: I, O, S, and five tiles within the sub-grid marked <code>?</code>.</li>
+</ul>
+<p>The rules about bugs living and dying are the same as before.</p>
+<p>For example, consider the same initial state as above:</p>
+<pre><code>....#
+#..#.
+#.?##
+..#..
+#....
+</code></pre>
+<p>The center tile is drawn as <code>?</code> to indicate the next recursive grid. Call this level 0; the grid within this one is level 1, and the grid that contains this one is level -1. Then, after <em>ten</em> minutes, the grid at each level would look like this:</p>
+<pre><code>Depth -5:
+..#..
+.#.#.
+..?.#
+.#.#.
+..#..
+
+Depth -4:
+...#.
+...##
+..?..
+...##
+...#.
+
+Depth -3:
+#.#..
+.#...
+..?..
+.#...
+#.#..
+
+Depth -2:
+.#.##
+....#
+..?.#
+...##
+.###.
+
+Depth -1:
+#..##
+...##
+..?..
+...#.
+.####
+
+Depth 0:
+.#...
+.#.##
+.#?..
+.....
+.....
+
+Depth 1:
+.##..
+#..##
+..?.#
+##.##
+#####
+
+Depth 2:
+###..
+##.#.
+#.?..
+.#.##
+#.#..
+
+Depth 3:
+..###
+.....
+#.?..
+#....
+#...#
+
+Depth 4:
+.###.
+#..#.
+#.?..
+##.#.
+.....
+
+Depth 5:
+####.
+#..#.
+#.?#.
+####.
+.....
+</code></pre>
+<p>In this example, after 10 minutes, a total of <code><em>99</em></code> bugs are present.</p>
+<p>Starting with your scan, <em>how many bugs are present after 200 minutes?</em></p>
+</article>
+<p>Your puzzle answer was <code>1937</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="/2019">return to your Advent calendar</a> and try another puzzle.</p>
+<p>If you still want to see it, you can <a href="24/input" target="_blank">get your puzzle input</a>.</p>
+<p>You can also <span class="share">[Share<span class="share-content">on
+ <a href="https://twitter.com/intent/tweet?text=I%27ve+completed+%22Planet+of+Discord%22+%2D+Day+24+%2D+Advent+of+Code+2019&url=https%3A%2F%2Fadventofcode%2Ecom%2F2019%2Fday%2F24&related=ericwastl&hashtags=AdventOfCode" target="_blank">Twitter</a>
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+></span>]</span> this puzzle.</p>
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