200 lines
7.7 KiB
HTML
200 lines
7.7 KiB
HTML
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<meta charset="utf-8"/>
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<title>Day 11 - Advent of Code 2020</title>
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</head><!--
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Oh, hello! Funny seeing you here.
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I appreciate your enthusiasm, but you aren't going to find much down here.
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There certainly aren't clues to any of the puzzles. The best surprises don't
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even appear in the source until you unlock them for real.
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Please be careful with automated requests; I'm not a massive company, and I can
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only take so much traffic. Please be considerate so that everyone gets to play.
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If you're curious about how Advent of Code works, it's running on some custom
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Perl code. Other than a few integrations (auth, analytics, social media), I
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built the whole thing myself, including the design, animations, prose, and all
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of the puzzles.
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The puzzles are most of the work; preparing a new calendar and a new set of
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puzzles each year takes all of my free time for 4-5 months. A lot of effort
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went into building this thing - I hope you're enjoying playing it as much as I
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enjoyed making it for you!
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If you'd like to hang out, I'm @ericwastl on Twitter.
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- Eric Wastl
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-->
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<body>
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<header><div><h1 class="title-global"><a href="/">Advent of Code</a></h1><nav><ul><li><a href="/2020/about">[About]</a></li><li><a href="/2020/events">[Events]</a></li><li><a href="https://teespring.com/stores/advent-of-code" target="_blank">[Shop]</a></li><li><a href="/2020/settings">[Settings]</a></li><li><a href="/2020/auth/logout">[Log Out]</a></li></ul></nav><div class="user">m42e <a href="/2020/support" class="supporter-badge" title="Advent of Code Supporter">(AoC++)</a> <span class="star-count">20*</span></div></div><div><h1 class="title-event"> <span class="title-event-wrap">0xffff&</span><a href="/2020">2020</a><span class="title-event-wrap"></span></h1><nav><ul><li><a href="/2020">[Calendar]</a></li><li><a href="/2020/support">[AoC++]</a></li><li><a href="/2020/sponsors">[Sponsors]</a></li><li><a href="/2020/leaderboard">[Leaderboard]</a></li><li><a href="/2020/stats">[Stats]</a></li></ul></nav></div></header>
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<div id="sidebar">
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<div id="sponsor"><div class="quiet">Our <a href="/2020/sponsors">sponsors</a> help make Advent of Code possible:</div><div class="sponsor"><a href="https://ximed.es/aoc" target="_blank" onclick="if(ga)ga('send','event','sponsor','sidebar',this.href);" rel="noopener">Ximedes</a> - From Kotlin in the cloud to embedded NodeJS, our software powers payments worldwide. Join us in the Netherlands or Serbia!</div></div>
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</div><!--/sidebar-->
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<main>
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<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>
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<article class="day-desc"><h2>--- Day 11: Seating System ---</h2><p>Your plane lands with plenty of time to spare. The final leg of your journey is a ferry that goes directly to the tropical island where you can finally start your vacation. As you reach the waiting area to board the ferry, you realize you're so early, nobody else has even arrived yet!</p>
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<p>By modeling the process people use to choose (or abandon) their seat in the waiting area, you're pretty sure you can predict the best place to sit. You make a quick map of the seat layout (your puzzle input).</p>
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<p>The seat layout fits neatly on a grid. Each position is either floor (<code>.</code>), an empty seat (<code>L</code>), or an occupied seat (<code>#</code>). For example, the initial seat layout might look like this:</p>
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<pre><code>L.LL.LL.LL
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LLLLLLL.LL
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L.L.L..L..
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LLLL.LL.LL
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L.LL.LL.LL
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L.LLLLL.LL
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..L.L.....
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LLLLLLLLLL
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L.LLLLLL.L
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L.LLLLL.LL
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</code></pre>
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<p>Now, you just need to model the people who will be arriving shortly. Fortunately, people are entirely predictable and always follow a simple set of rules. All decisions are based on the <em>number of occupied seats</em> adjacent to a given seat (one of the eight positions immediately up, down, left, right, or diagonal from the seat). The following rules are applied to every seat simultaneously:</p>
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<ul>
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<li>If a seat is <em>empty</em> (<code>L</code>) and there are <em>no</em> occupied seats adjacent to it, the seat becomes <em>occupied</em>.</li>
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<li>If a seat is <em>occupied</em> (<code>#</code>) and <em>four or more</em> seats adjacent to it are also occupied, the seat becomes <em>empty</em>.</li>
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<li>Otherwise, the seat's state does not change.</li>
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</ul>
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<p><span title="Floor... floor never changes.">Floor (<code>.</code>) never changes</span>; seats don't move, and nobody sits on the floor.</p>
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<p>After one round of these rules, every seat in the example layout becomes occupied:</p>
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<pre><code>#.##.##.##
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#######.##
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#.#.#..#..
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####.##.##
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#.##.##.##
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#.#####.##
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..#.#.....
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##########
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#.######.#
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#.#####.##
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</code></pre>
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<p>After a second round, the seats with four or more occupied adjacent seats become empty again:</p>
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<pre><code>#.LL.L#.##
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#LLLLLL.L#
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L.L.L..L..
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#LLL.LL.L#
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#.LL.LL.LL
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#.LLLL#.##
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..L.L.....
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#LLLLLLLL#
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#.LLLLLL.L
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#.#LLLL.##
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</code></pre>
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<p>This process continues for three more rounds:</p>
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<pre><code>#.##.L#.##
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#L###LL.L#
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L.#.#..#..
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#L##.##.L#
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#.##.LL.LL
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#.###L#.##
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..#.#.....
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#L######L#
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#.LL###L.L
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#.#L###.##
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</code></pre>
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<pre><code>#.#L.L#.##
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#LLL#LL.L#
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L.L.L..#..
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#LLL.##.L#
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#.LL.LL.LL
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#.LL#L#.##
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..L.L.....
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#L#LLLL#L#
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#.LLLLLL.L
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#.#L#L#.##
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</code></pre>
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<pre><code>#.#L.L#.##
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#LLL#LL.L#
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L.#.L..#..
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#L##.##.L#
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#.#L.LL.LL
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#.#L#L#.##
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..L.L.....
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#L#L##L#L#
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#.LLLLLL.L
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#.#L#L#.##
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</code></pre>
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<p>At this point, something interesting happens: the chaos stabilizes and further applications of these rules cause no seats to change state! Once people stop moving around, you count <em><code>37</code></em> occupied seats.</p>
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<p>Simulate your seating area by applying the seating rules repeatedly until no seats change state. <em>How many seats end up occupied?</em></p>
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</article>
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<p>To begin, <a href="11/input" target="_blank">get your puzzle input</a>.</p>
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<form method="post" action="11/answer"><input type="hidden" name="level" value="1"/><p>Answer: <input type="text" name="answer" autocomplete="off"/> <input type="submit" value="[Submit]"/></p></form>
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<p>You can also <span class="share">[Share<span class="share-content">on
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<a href="https://twitter.com/intent/tweet?text=%22Seating+System%22+%2D+Day+11+%2D+Advent+of+Code+2020&url=https%3A%2F%2Fadventofcode%2Ecom%2F2020%2Fday%2F11&related=ericwastl&hashtags=AdventOfCode" target="_blank">Twitter</a>
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<a href="javascript:void(0);" onclick="var mastodon_instance=prompt('Mastodon Instance / Server Name?'); if(typeof mastodon_instance==='string' && mastodon_instance.length){this.href='https://'+mastodon_instance+'/share?text=%22Seating+System%22+%2D+Day+11+%2D+Advent+of+Code+2020+%23AdventOfCode+https%3A%2F%2Fadventofcode%2Ecom%2F2020%2Fday%2F11'}else{return false;}" target="_blank">Mastodon</a
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></span>]</span> this puzzle.</p>
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