d08a.html

<article class="day-desc">
 <h2>
  --- Day 8: Haunted Wasteland ---
 </h2>
 <p>
  You&#39;re still riding a camel across Desert Island when you spot a sandstorm quickly approaching. When you turn to warn the Elf, she disappears before your eyes! To be fair, she had just finished warning you about
  <em>
   ghosts
  </em>
  a few minutes ago.
 </p>
 <p>
  One of the camel&#39;s pouches is labeled &#34;maps&#34; - sure enough, it&#39;s full of documents (your puzzle input) about how to navigate the desert. At least, you&#39;re pretty sure that&#39;s what they are; one of the documents contains a list of left/right instructions, and the rest of the documents seem to describe some kind of
  <em>
   network
  </em>
  of labeled nodes.
 </p>
 <p>
  It seems like you&#39;re meant to use the
  <em>
   left/right
  </em>
  instructions to
  <em>
   navigate the network
  </em>
  . Perhaps if you have the camel follow the same instructions, you can escape the haunted wasteland!
 </p>
 <p>
  After examining the maps for a bit, two nodes stick out:
  <code>
   AAA
  </code>
  and
  <code>
   ZZZ
  </code>
  . You feel like
  <code>
   AAA
  </code>
  is where you are now, and you have to follow the left/right instructions until you reach
  <code>
   ZZZ
  </code>
  .
 </p>
 <p>
  This format defines each
  <em>
   node
  </em>
  of the network individually. For example:
 </p>
 <pre>
  <code>
   RL

AAA = (BBB, CCC)
BBB = (DDD, EEE)
CCC = (ZZZ, GGG)
DDD = (DDD, DDD)
EEE = (EEE, EEE)
GGG = (GGG, GGG)
ZZZ = (ZZZ, ZZZ)
  </code>
 </pre>
 <p>
  Starting with
  <code>
   AAA
  </code>
  , you need to
  <em>
   look up the next element
  </em>
  based on the next left/right instruction in your input. In this example, start with
  <code>
   AAA
  </code>
  and go
  <em>
   right
  </em>
  (
  <code>
   R
  </code>
  ) by choosing the right element of
  <code>
   AAA
  </code>
  ,
  <code>
   <em>
    CCC
   </em>
  </code>
  . Then,
  <code>
   L
  </code>
  means to choose the
  <em>
   left
  </em>
  element of
  <code>
   CCC
  </code>
  ,
  <code>
   <em>
    ZZZ
   </em>
  </code>
  . By following the left/right instructions, you reach
  <code>
   ZZZ
  </code>
  in
  <code>
   <em>
    2
   </em>
  </code>
  steps.
 </p>
 <p>
  Of course, you might not find
  <code>
   ZZZ
  </code>
  right away. If you run out of left/right instructions, repeat the whole sequence of instructions as necessary:
  <code>
   RL
  </code>
  really means
  <code>
   RLRLRLRLRLRLRLRL...
  </code>
  and so on. For example, here is a situation that takes
  <code>
   <em>
    6
   </em>
  </code>
  steps to reach
  <code>
   ZZZ
  </code>
  :
 </p>
 <pre>
  <code>
   LLR

AAA = (BBB, BBB)
BBB = (AAA, ZZZ)
ZZZ = (ZZZ, ZZZ)
  </code>
 </pre>
 <p>
  Starting at
  <code>
   AAA
  </code>
  , follow the left/right instructions.
  <em>
   How many steps are required to reach
   <code>
    ZZZ
   </code>
   ?
  </em>
 </p>
</article>