day12.html

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   5 <title>Day 12 - Advent of Code 2016</title>
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  15 Oh, hello!  Funny seeing you here.
  16
  17 I appreciate your enthusiasm, but you aren't going to find much down here.
  18 There certainly aren't clues to any of the puzzles.  The best surprises don't
  19 even appear in the source until you unlock them for real.
  20
  21 Please be careful with automated requests; I'm not Google, and I can only take
  22 so much traffic.  Please be considerate so that everyone gets to play.
  23
  24 If you're curious about how Advent of Code works, it's running on some custom
  25 Perl code. Other than a few integrations (auth, analytics, ads, social media),
  26 I built the whole thing myself, including the design, animations, prose, and
  27 all of the puzzles.
  28
  29 The puzzles probably took the longest; the easiest ones were around 45 minutes
  30 each, but the harder ones took 2-3 hours, and a few even longer than that. A
  31 lot of effort went into building this thing - I hope you're enjoying playing it
  32 as much as I enjoyed making it for you!
  33
  34 If you'd like to hang out, I'm @ericwastl on Twitter.
  35
  36 - Eric Wastl
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  88 <body>
  89 <header><div><h1 class="title-global"><a href="/">Advent of Code</a></h1><nav><ul><li><a href="/2016/about">[About]</a></li><li><a href="/2016/support">[AoC++]</a></li><li><a href="/2016/events">[Events]</a></li><li><a href="/2016/settings">[Settings]</a></li><li><a href="/2016/auth/logout">[Log Out]</a></li></ul></nav><div class="user">Neil Smith <span class="supporter">(AoC++)</span> <span class="star-count">24*</span></div></div><div><h1 class="title-event">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="title-event-wrap">//</span><a href="/2016">2016</a><span class="title-event-wrap"></span></h1><nav><ul><li><a href="/2016">[Calendar]</a></li><li><a href="/2016/leaderboard">[Leaderboard]</a></li><li><a href="/2016/stats">[Stats]</a></li><li><a href="/2016/sponsors">[Sponsors]</a></li></ul></nav></div></header>
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  92 <div id="sponsor"><div class="quiet">Our <a href="/2016/sponsors">sponsors</a> help make AoC possible:</div><p><a href="https://info.esparklearning.com/join-our-team-full-stack-engineer" target="_blank" onclick="if(ga)ga('send','event','sponsor','click',this.href);">eSpark Learning</a> - Solve the greatest puzzle of our day - transform education</p></div>
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 107 <article class="day-desc"><h2>--- Day 12: Leonardo's Monorail ---</h2><p>You finally reach the top floor of this building: a garden with a slanted glass ceiling. Looks like there are no more stars to be had.</p>
 108 <p>While sitting on a nearby bench amidst some <a href="https://www.google.com/search?q=tiger+lilies&tbm=isch">tiger lilies</a>, you manage to decrypt some of the files you extracted from the servers downstairs.</p>
 109 <p>According to these documents, Easter Bunny HQ isn't just this building - it's a collection of buildings in the nearby area. They're all connected by a local monorail, and there's another building not far from here! Unfortunately, being night, the monorail is currently not operating.</p>
 110 <p>You remotely connect to the monorail control systems and discover that the boot sequence expects a password. The password-checking logic (your puzzle input) is easy to extract, but the code it uses is strange: it's <span title="Strangely, this assembunny code doesn't seem to be very good at multiplying.">assembunny</span> code designed for the <a href="11">new computer</a> you just assembled. You'll have to execute the code and get the password.</p>
 111 <p>The assembunny code you've extracted operates on four <a href="https://en.wikipedia.org/wiki/Processor_register">registers</a> (<code>a</code>, <code>b</code>, <code>c</code>, and <code>d</code>) that start at <code>0</code> and can hold any <a href="https://en.wikipedia.org/wiki/Integer">integer</a>. However, it seems to make use of only a few <a href="https://en.wikipedia.org/wiki/Instruction_set">instructions</a>:</p>
 112 <ul>
 113 <li><code>cpy x y</code> <em>copies</em> <code>x</code> (either an integer or the <em>value</em> of a register) into register <code>y</code>.</li>
 114 <li><code>inc x</code> <em>increases</em> the value of register <code>x</code> by one.</li>
 115 <li><code>dec x</code> <em>decreases</em> the value of register <code>x</code> by one.</li>
 116 <li><code>jnz x y</code> <em>jumps</em> to an instruction <code>y</code> away (positive means forward; negative means backward), but only if <code>x</code> is <em>not zero</em>.</li>
 117 </ul>
 118 <p>The <code>jnz</code> instruction moves relative to itself: an offset of <code>-1</code> would continue at the previous instruction, while an offset of <code>2</code> would <em>skip over</em> the next instruction.</p>
 119 <p>For example:</p>
 120 <pre><code>cpy 41 a
 121 inc a
 122 inc a
 123 dec a
 124 jnz a 2
 125 dec a
 126 </code></pre>
 127 <p>The above code would set register <code>a</code> to <code>41</code>, increase its value by <code>2</code>, decrease its value by <code>1</code>, and then skip the last <code>dec a</code> (because <code>a</code> is not zero, so the <code>jnz a 2</code> skips it), leaving register <code>a</code> at <code>42</code>. When you move past the last instruction, the program halts.</p>
 128 <p>After executing the assembunny code in your puzzle input, <em>what value is left in register <code>a</code>?</em></p>
 129 </article>
 130 <p>Your puzzle answer was <code>318009</code>.</p><article class="day-desc"><h2>--- Part Two ---</h2><p>As you head down the fire escape to the monorail, you notice it didn't start; register <code>c</code> needs to be initialized to the position of the ignition key.</p>
 131 <p>If you instead <em>initialize register <code>c</code> to be <code>1</code></em>, what value is now left in register <code>a</code>?</p>
 132 </article>
 133 <p>Your puzzle answer was <code>9227663</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
 134 <p>At this point, you should <a href="/2016">return to your advent calendar</a> and try another puzzle.</p>
 135 <p>If you still want to see it, you can <a href="12/input" target="_blank">get your puzzle input</a>.</p>
 136 <p>You can also <span class="share">[Share<span class="share-content">on
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 140 ></span>]</span> this puzzle.</p>
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