2015adventofcode/23.htm at master · benblankley/2015adventofcode · GitHub

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<title>Day 23 - Advent of Code</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.  You do risk spoiling a few
surprises for yourself, though.  Best to play the normal way and discover
everything as it was intended, I think.  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 Google, 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, ads, social media),
I built the whole thing myself, including the design, animations, prose, and
all of the puzzles.

The puzzles probably took the longest; the easiest ones were around 45 minutes
each, but the harder ones took 2-3 hours, some even longer than that. 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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<header><h1><a href="/">Advent of Code</a></h1><div class="user">Ben Blankley <span class="star-count">12*</span></div><nav><ul><li><a href="/about">[About]</a></li><li><a href="/stats">[Stats]</a></li><li><a href="/leaderboard">[Leaderboard]</a></li><li><a href="/settings">[Settings]</a></li><li><a href="/auth/logout">[Log out]</a></li></ul></nav></header>

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<article class="day-desc"><h2>--- Day 23: Opening the Turing Lock ---</h2><p>Little Jane Marie just got her very first computer for Christmas from some <span title="Definitely not Wintermute.">unknown benefactor</span>.  It comes with instructions and an example program, but the computer itself seems to be malfunctioning.  She's curious what the program does, and would like you to help her run it.</p>
<p>The manual explains that the computer supports two <a href="https://en.wikipedia.org/wiki/Processor_register">registers</a> and six <a href="https://en.wikipedia.org/wiki/Instruction_set">instructions</a> (truly, it goes on to remind the reader, a state-of-the-art technology). The registers are named <code>a</code> and <code>b</code>, can hold any <a href="https://en.wikipedia.org/wiki/Natural_number">non-negative integer</a>, and begin with a value of <code>0</code>.  The instructions are as follows:</p>
<ul>
<li><code>hlf r</code> sets register <code>r</code> to <em>half</em> its current value, then continues with the next instruction.</li>
<li><code>tpl r</code> sets register <code>r</code> to <em>triple</em> its current value, then continues with the next instruction.</li>
<li><code>inc r</code> <em>increments</em> register <code>r</code>, adding <code>1</code> to it, then continues with the next instruction.</li>
<li><code>jmp offset</code> is a <em>jump</em>; it continues with the instruction <code>offset</code> away <em>relative to itself</em>.</li>
<li><code>jie r, offset</code> is like <code>jmp</code>, but only jumps if register <code>r</code> is <em>even</em> ("jump if even").</li>
<li><code>jio r, offset</code> is like <code>jmp</code>, but only jumps if register <code>r</code> is <code>1</code> ("jump if <em>one</em>", not odd).</li>
</ul>
<p>All three jump instructions work with an <em>offset</em> relative to that instruction.  The offset is always written with a prefix <code>+</code> or <code>-</code> to indicate the direction of the jump (forward or backward, respectively).  For example, <code>jmp +1</code> would simply continue with the next instruction, while <code>jmp +0</code> would continuously jump back to itself forever.</p>
<p>The program exits when it tries to run an instruction beyond the ones defined.</p>
<p>For example, this program sets <code>a</code> to <code>2</code>, because the <code>jio</code> instruction causes it to skip the <code>tpl</code> instruction:</p>
<pre><code>inc a
jio a, +2
tpl a
inc a
</code></pre>
<p>What is <em>the value in register <code>b</code></em> when the program in your puzzle input is finished executing?</p>
</article>
<p>To begin, <a href="/day/23/input" target="_blank">get your puzzle input</a>.</p>
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