problems/day16.html

   1 <!DOCTYPE html>
   2 <html lang="en-us">
   3 <head>
   4 <meta charset="utf-8"/>
   5 <title>Day 16 - Advent of Code 2020</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?25"/>
   9 <link rel="stylesheet alternate" type="text/css" href="/static/highcontrast.css?0" title="High Contrast"/>
  10 <link rel="shortcut icon" href="/favicon.png"/>
  11 </head><!--
  12
  13
  14
  15
  16 Oh, hello!  Funny seeing you here.
  17
  18 I appreciate your enthusiasm, but you aren't going to find much down here.
  19 There certainly aren't clues to any of the puzzles.  The best surprises don't
  20 even appear in the source until you unlock them for real.
  21
  22 Please be careful with automated requests; I'm not a massive company, and I can
  23 only take so much traffic.  Please be considerate so that everyone gets to play.
  24
  25 If you're curious about how Advent of Code works, it's running on some custom
  26 Perl code. Other than a few integrations (auth, analytics, social media), I
  27 built the whole thing myself, including the design, animations, prose, and all
  28 of the puzzles.
  29
  30 The puzzles are most of the work; preparing a new calendar and a new set of
  31 puzzles each year takes all of my free time for 4-5 months. A lot of effort
  32 went into building this thing - I hope you're enjoying playing it as much as I
  33 enjoyed making it for you!
  34
  35 If you'd like to hang out, I'm @ericwastl on Twitter.
  36
  37 - Eric Wastl
  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 -->
  89 <body>
  90 <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">Neil Smith <a href="/2020/support" class="supporter-badge" title="Advent of Code Supporter">(AoC++)</a> <span class="star-count">32*</span></div></div><div><h1 class="title-event">&nbsp;&nbsp;&nbsp;<span class="title-event-wrap">0x0000|</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>
  91
  92 <div id="sidebar">
  93 <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://github.com/" target="_blank" onclick="if(ga)ga('send','event','sponsor','sidebar',this.href);" rel="noopener">GitHub</a> - We&apos;re hiring engineers to make GitHub fast. Interested? Email fast@github.com with details of exceptional performance work you&apos;ve done in the past.</div></div>
  94 </div><!--/sidebar-->
  95
  96 <main>
  97 <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>
  98 <article class="day-desc"><h2>--- Day 16: Ticket Translation ---</h2><p>As you're walking to yet another connecting flight, you realize that one of the legs of your re-routed trip coming up is on a high-speed train. However, the train ticket you were given is in a language you don't understand. You should probably figure out what it says before you get to the train station after the next flight.</p>
  99 <p>Unfortunately, you <span title="This actually happened to me once, but I solved it by just asking someone.">can't actually <em>read</em> the words on the ticket</span>. You can, however, read the numbers, and so you figure out <em>the fields these tickets must have</em> and <em>the valid ranges</em> for values in those fields.</p>
 100 <p>You collect the <em>rules for ticket fields</em>, the <em>numbers on your ticket</em>, and the <em>numbers on other nearby tickets</em> for the same train service (via the airport security cameras) together into a single document you can reference (your puzzle input).</p>
 101 <p>The <em>rules for ticket fields</em> specify a list of fields that exist <em>somewhere</em> on the ticket and the <em>valid ranges of values</em> for each field. For example, a rule like <code>class: 1-3 or 5-7</code> means that one of the fields in every ticket is named <code>class</code> and can be any value in the ranges <code>1-3</code> or <code>5-7</code> (inclusive, such that <code>3</code> and <code>5</code> are both valid in this field, but <code>4</code> is not).</p>
 102 <p>Each ticket is represented by a single line of comma-separated values. The values are the numbers on the ticket in the order they appear; every ticket has the same format. For example, consider this ticket:</p>
 103 <pre><code>.--------------------------------------------------------.
 104 | ????: 101    ?????: 102   ??????????: 103     ???: 104 |
 105 |                                                        |
 106 | ??: 301  ??: 302             ???????: 303      ??????? |
 107 | ??: 401  ??: 402           ???? ????: 403    ????????? |
 108 '--------------------------------------------------------'
 109 </code></pre>
 110 <p>Here, <code>?</code> represents text in a language you don't understand. This ticket might be represented as <code>101,102,103,104,301,302,303,401,402,403</code>; of course, the actual train tickets you're looking at are <em>much</em> more complicated. In any case, you've extracted just the numbers in such a way that the first number is always the same specific field, the second number is always a different specific field, and so on - you just don't know what each position actually means!</p>
 111 <p>Start by determining which tickets are <em>completely invalid</em>; these are tickets that contain values which <em>aren't valid for any field</em>. Ignore <em>your ticket</em> for now.</p>
 112 <p>For example, suppose you have the following notes:</p>
 113 <pre><code>class: 1-3 or 5-7
 114 row: 6-11 or 33-44
 115 seat: 13-40 or 45-50
 116
 117 your ticket:
 118 7,1,14
 119
 120 nearby tickets:
 121 7,3,47
 122 40,<em>4</em>,50
 123 <em>55</em>,2,20
 124 38,6,<em>12</em>
 125 </code></pre>
 126 <p>It doesn't matter which position corresponds to which field; you can identify invalid <em>nearby tickets</em> by considering only whether tickets contain <em>values that are not valid for any field</em>. In this example, the values on the first <em>nearby ticket</em> are all valid for at least one field. This is not true of the other three <em>nearby tickets</em>: the values <code>4</code>, <code>55</code>, and <code>12</code> are are not valid for any field. Adding together all of the invalid values produces your <em>ticket scanning error rate</em>: <code>4 + 55 + 12</code> = <em><code>71</code></em>.</p>
 127 <p>Consider the validity of the <em>nearby tickets</em> you scanned. <em>What is your ticket scanning error rate?</em></p>
 128 </article>
 129 <p>Your puzzle answer was <code>25984</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>Now that you've identified which tickets contain invalid values, <em>discard those tickets entirely</em>. Use the remaining valid tickets to determine which field is which.</p>
 130 <p>Using the valid ranges for each field, determine what order the fields appear on the tickets. The order is consistent between all tickets: if <code>seat</code> is the third field, it is the third field on every ticket, including <em>your ticket</em>.</p>
 131 <p>For example, suppose you have the following notes:</p>
 132 <pre><code>class: 0-1 or 4-19
 133 row: 0-5 or 8-19
 134 seat: 0-13 or 16-19
 135
 136 your ticket:
 137 11,12,13
 138
 139 nearby tickets:
 140 3,9,18
 141 15,1,5
 142 5,14,9
 143 </code></pre>
 144 <p>Based on the <em>nearby tickets</em> in the above example, the first position must be <code>row</code>, the second position must be <code>class</code>, and the third position must be <code>seat</code>; you can conclude that in <em>your ticket</em>, <code>class</code> is <code>12</code>, <code>row</code> is <code>11</code>, and <code>seat</code> is <code>13</code>.</p>
 145 <p>Once you work out which field is which, look for the six fields on <em>your ticket</em> that start with the word <code>departure</code>. <em>What do you get if you multiply those six values together?</em></p>
 146 </article>
 147 <p>Your puzzle answer was <code>1265347500049</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
 148 <p>At this point, you should <a href="/2020">return to your Advent calendar</a> and try another puzzle.</p>
 149 <p>If you still want to see it, you can <a href="16/input" target="_blank">get your puzzle input</a>.</p>
 150 <p>You can also <span class="share">[Share<span class="share-content">on
 151   <a href="https://twitter.com/intent/tweet?text=I%27ve+completed+%22Ticket+Translation%22+%2D+Day+16+%2D+Advent+of+Code+2020&amp;url=https%3A%2F%2Fadventofcode%2Ecom%2F2020%2Fday%2F16&amp;related=ericwastl&amp;hashtags=AdventOfCode" target="_blank">Twitter</a>
 152   <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=I%27ve+completed+%22Ticket+Translation%22+%2D+Day+16+%2D+Advent+of+Code+2020+%23AdventOfCode+https%3A%2F%2Fadventofcode%2Ecom%2F2020%2Fday%2F16'}else{return false;}" target="_blank">Mastodon</a
 153 ></span>]</span> this puzzle.</p>
 154 </main>
 155
 156 <!-- ga -->
 157 <script>
 158 (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
 159 (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
 160 m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
 161 })(window,document,'script','//www.google-analytics.com/analytics.js','ga');
 162 ga('create', 'UA-69522494-1', 'auto');
 163 ga('set', 'anonymizeIp', true);
 164 ga('send', 'pageview');
 165 </script>
 166 <!-- /ga -->
 167 </body>
 168 </html>