day21.html

   1 <!DOCTYPE html>
   2 <html lang="en-us">
   3 <head>
   4 <meta charset="utf-8"/>
   5 <title>Day 21 - Advent of Code 2016</title>
   6 <!--[if lt IE 9]><script src="/static/html5.js"></script><![endif]-->
   7 <link href='//fonts.googleapis.com/css?family=Source+Code+Pro:300&subset=latin,latin-ext' rel='stylesheet' type='text/css'>
   8 <link rel="stylesheet" type="text/css" href="/static/style.css?9"/>
   9 <link rel="shortcut icon" href="/favicon.ico?2"/>
  10 </head><!--
  11
  12
  13
  14
  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
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87 -->
  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">42*</span></div></div><div><h1 class="title-event">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="title-event-wrap">y(</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>
  90
  91 <div id="sidebar">
  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>
  93 <div id="ad">
  94 <script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
  95 <!-- Advent of Code Wide Skyscraper -->
  96 <ins class="adsbygoogle"
  97      style="display:inline-block;width:160px;height:600px"
  98      data-ad-client="ca-pub-9420604735624631"
  99      data-ad-slot="8014013294"></ins>
 100 <script>
 101 (adsbygoogle = window.adsbygoogle || []).push({});
 102 </script>
 103 </div><!--/ad-->
 104 </div><!--/sidebar-->
 105
 106 <main>
 107 <article class="day-desc"><h2>--- Day 21: Scrambled Letters and Hash ---</h2><p>The computer system you're breaking into uses a <span title="I do not like them, Security-Account-Manager-I-Am! I do not like scrambled letters and hash!">weird scrambling function</span> to store its passwords. It shouldn't be much trouble to create your own scrambled password so you can add it to the system; you just have to implement the scrambler.</p>
 108 <p>The scrambling function is a series of operations (the exact list is provided in your puzzle input). Starting with the password to be scrambled, apply each operation in succession to the string. The individual operations behave as follows:</p>
 109 <ul>
 110 <li><code>swap position X with position Y</code> means that the letters at indexes <code>X</code> and <code>Y</code> (counting from <code>0</code>) should be <em>swapped</em>.</li>
 111 <li><code>swap letter X with letter Y</code> means that the letters <code>X</code> and <code>Y</code> should be <em>swapped</em> (regardless of where they appear in the string).</li>
 112 <li><code>rotate left/right X steps</code> means that the whole string should be <em>rotated</em>; for example, one right rotation would turn <code>abcd</code> into <code>dabc</code>.</li>
 113 <li><code>rotate based on position of letter X</code> means that the whole string should be <em>rotated to the right</em> based on the <em>index</em> of letter <code>X</code> (counting from <code>0</code>) as determined <em>before</em> this instruction does any rotations.  Once the index is determined, rotate the string to the right one time, plus a number of times equal to that index, plus one additional time if the index was at least <code>4</code>.</li>
 114 <li><code>reverse positions X through Y</code> means that the span of letters at indexes <code>X</code> through <code>Y</code> (including the letters at <code>X</code> and <code>Y</code>) should be <em>reversed in order</em>.</li>
 115 <li><code>move position X to position Y</code> means that the letter which is at index <code>X</code> should be <em>removed</em> from the string, then <em>inserted</em> such that it ends up at index <code>Y</code>.</li>
 116 </ul>
 117 <p>For example, suppose you start with <code>abcde</code> and perform the following operations:</p>
 118 <ul>
 119 <li><code>swap position 4 with position 0</code> swaps the first and last letters, producing the input for the next step, <code>ebcda</code>.</li>
 120 <li><code>swap letter d with letter b</code> swaps the positions of <code>d</code> and <code>b</code>: <code>edcba</code>.</li>
 121 <li><code>reverse positions 0 through 4</code> causes the entire string to be reversed, producing <code>abcde</code>.</li>
 122 <li><code>rotate left 1 step</code> shifts all letters left one position, causing the first letter to wrap to the end of the string: <code>bcdea</code>.</li>
 123 <li><code>move position 1 to position 4</code> removes the letter at position <code>1</code> (<code>c</code>), then inserts it at position <code>4</code> (the end of the string): <code>bdeac</code>.</li>
 124 <li><code>move position 3 to position 0</code> removes the letter at position <code>3</code> (<code>a</code>), then inserts it at position <code>0</code> (the front of the string): <code>abdec</code>.</li>
 125 <li><code>rotate based on position of letter b</code> finds the index of letter <code>b</code> (<code>1</code>), then rotates the string right once plus a number of times equal to that index (<code>2</code>): <code>ecabd</code>.</li>
 126 <li><code>rotate based on position of letter d</code> finds the index of letter <code>d</code> (<code>4</code>), then rotates the string right once, plus a number of times equal to that index, plus an additional time because the index was at least <code>4</code>, for a total of <code>6</code> right rotations: <code>decab</code>.</li>
 127 </ul>
 128 <p>After these steps, the resulting scrambled password is <code>decab</code>.</p>
 129 <p>Now, you just need to generate a new scrambled password and you can access the system. Given the list of scrambling operations in your puzzle input, <em>what is the result of scrambling <code>abcdefgh</code></em>?</p>
 130 </article>
 131 <p>Your puzzle answer was <code>aefgbcdh</code>.</p><article class="day-desc"><h2>--- Part Two ---</h2><p>You scrambled the password correctly, but you discover that you <a href="https://en.wikipedia.org/wiki/File_system_permissions">can't actually modify</a> the <a href="https://en.wikipedia.org/wiki/Passwd">password file</a> on the system. You'll need to un-scramble one of the existing passwords by reversing the scrambling process.</p>
 132 <p>What is the un-scrambled version of the scrambled password <code>fbgdceah</code>?</p>
 133 </article>
 134 <p>Your puzzle answer was <code>egcdahbf</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
 135 <p>At this point, you should <a href="/2016">return to your advent calendar</a> and try another puzzle.</p>
 136 <p>If you still want to see it, you can <a href="21/input" target="_blank">get your puzzle input</a>.</p>
 137 <p>You can also <span class="share">[Share<span class="share-content">on
 138   <a href="https://twitter.com/intent/tweet?text=I%27ve+completed+%22Scrambled+Letters+and+Hash%22+%2D+Day+21+%2D+Advent+of+Code+2016&amp;url=http%3A%2F%2Fadventofcode%2Ecom%2F2016%2Fday%2F21&amp;related=ericwastl&amp;hashtags=AdventOfCode" target="_blank">Twitter</a>
 139   <a href="https://plus.google.com/share?url=http%3A%2F%2Fadventofcode%2Ecom%2F2016%2Fday%2F21" target="_blank">Google+</a>
 140   <a href="http://www.reddit.com/submit?url=http%3A%2F%2Fadventofcode%2Ecom%2F2016%2Fday%2F21&amp;title=I%27ve+completed+%22Scrambled+Letters+and+Hash%22+%2D+Day+21+%2D+Advent+of+Code+2016" target="_blank">Reddit</a
 141 ></span>]</span> this puzzle.</p>
 142 </main>
 143
 144 <!-- ga -->
 145 <script>
 146 (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
 147 (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
 148 m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
 149 })(window,document,'script','//www.google-analytics.com/analytics.js','ga');
 150 ga('create', 'UA-69522494-1', 'auto');
 151 ga('send', 'pageview');
 152 </script>
 153 <!-- /ga -->
 154 </body>
 155 </html>