problems/day03.html

   1 <!DOCTYPE html>
   2 <html lang="en-us">
   3 <head>
   4 <meta charset="utf-8"/>
   5 <title>Day 3 - 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">6*</span></div></div><div><h1 class="title-event">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="title-event-wrap">y(</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://www.codethink.co.uk/" target="_blank" onclick="if(ga)ga('send','event','sponsor','sidebar',this.href);" rel="noopener">Codethink</a> - Codethink is a software services company, expert in the use of Open Source technologies for systems software engineering.</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 3: Toboggan Trajectory ---</h2><p>With the toboggan login problems resolved, you set off toward the airport. While travel by toboggan might be easy, it's certainly not safe: there's <span title="It looks like the toboggan steering system even runs on Intcode! Good thing you don't have to modify it.">very minimal steering</span> and the area is covered in trees. You'll need to see which angles will take you near the fewest trees.</p>
  99 <p>Due to the local geology, trees in this area only grow on exact integer coordinates in a grid. You make a map (your puzzle input) of the open squares (<code>.</code>) and trees (<code>#</code>) you can see. For example:</p>
 100 <pre><code>..##.......
 101 #...#...#..
 102 .#....#..#.
 103 ..#.#...#.#
 104 .#...##..#.
 105 ..#.##.....
 106 .#.#.#....#
 107 .#........#
 108 #.##...#...
 109 #...##....#
 110 .#..#...#.#
 111 </code></pre>
 112 <p>These aren't the only trees, though; due to something you read about once involving arboreal genetics and biome stability, the same pattern repeats to the right many times:</p>
 113 <pre><code><em>..##.......</em>..##.........##.........##.........##.........##.......  ---&gt;
 114 <em>#...#...#..</em>#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
 115 <em>.#....#..#.</em>.#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
 116 <em>..#.#...#.#</em>..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
 117 <em>.#...##..#.</em>.#...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
 118 <em>..#.##.....</em>..#.##.......#.##.......#.##.......#.##.......#.##.....  ---&gt;
 119 <em>.#.#.#....#</em>.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
 120 <em>.#........#</em>.#........#.#........#.#........#.#........#.#........#
 121 <em>#.##...#...</em>#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...
 122 <em>#...##....#</em>#...##....##...##....##...##....##...##....##...##....#
 123 <em>.#..#...#.#</em>.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#  ---&gt;
 124 </code></pre>
 125 <p>You start on the open square (<code>.</code>) in the top-left corner and need to reach the bottom (below the bottom-most row on your map).</p>
 126 <p>The toboggan can only follow a few specific slopes (you opted for a cheaper model that prefers rational numbers); start by <em>counting all the trees</em> you would encounter for the slope <em>right 3, down 1</em>:</p>
 127 <p>From your starting position at the top-left, check the position that is right 3 and down 1. Then, check the position that is right 3 and down 1 from there, and so on until you go past the bottom of the map.</p>
 128 <p>The locations you'd check in the above example are marked here with <code><em>O</em></code> where there was an open square and <code><em>X</em></code> where there was a tree:</p>
 129 <pre><code>..##.........##.........##.........##.........##.........##.......  ---&gt;
 130 #..<em>O</em>#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
 131 .#....<em>X</em>..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
 132 ..#.#...#<em>O</em>#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
 133 .#...##..#..<em>X</em>...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
 134 ..#.##.......#.<em>X</em>#.......#.##.......#.##.......#.##.......#.##.....  ---&gt;
 135 .#.#.#....#.#.#.#.<em>O</em>..#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
 136 .#........#.#........<em>X</em>.#........#.#........#.#........#.#........#
 137 #.##...#...#.##...#...#.<em>X</em>#...#...#.##...#...#.##...#...#.##...#...
 138 #...##....##...##....##...#<em>X</em>....##...##....##...##....##...##....#
 139 .#..#...#.#.#..#...#.#.#..#...<em>X</em>.#.#..#...#.#.#..#...#.#.#..#...#.#  ---&gt;
 140 </code></pre>
 141 <p>In this example, traversing the map using this slope would cause you to encounter <code><em>7</em></code> trees.</p>
 142 <p>Starting at the top-left corner of your map and following a slope of right 3 and down 1, <em>how many trees would you encounter?</em></p>
 143 </article>
 144 <p>Your puzzle answer was <code>228</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>Time to check the rest of the slopes - you need to minimize the probability of a sudden arboreal stop, after all.</p>
 145 <p>Determine the number of trees you would encounter if, for each of the following slopes, you start at the top-left corner and traverse the map all the way to the bottom:</p>
 146 <ul>
 147 <li>Right 1, down 1.</li>
 148 <li>Right 3, down 1. (This is the slope you already checked.)</li>
 149 <li>Right 5, down 1.</li>
 150 <li>Right 7, down 1.</li>
 151 <li>Right 1, down 2.</li>
 152 </ul>
 153 <p>In the above example, these slopes would find <code>2</code>, <code>7</code>, <code>3</code>, <code>4</code>, and <code>2</code> tree(s) respectively; multiplied together, these produce the answer <code><em>336</em></code>.</p>
 154 <p><em>What do you get if you multiply together the number of trees encountered on each of the listed slopes?</em></p>
 155 </article>
 156 <p>Your puzzle answer was <code>6818112000</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
 157 <p>At this point, you should <a href="/2020">return to your Advent calendar</a> and try another puzzle.</p>
 158 <p>If you still want to see it, you can <a href="3/input" target="_blank">get your puzzle input</a>.</p>
 159 <p>You can also <span class="share">[Share<span class="share-content">on
 160   <a href="https://twitter.com/intent/tweet?text=I%27ve+completed+%22Toboggan+Trajectory%22+%2D+Day+3+%2D+Advent+of+Code+2020&amp;url=https%3A%2F%2Fadventofcode%2Ecom%2F2020%2Fday%2F3&amp;related=ericwastl&amp;hashtags=AdventOfCode" target="_blank">Twitter</a>
 161   <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+%22Toboggan+Trajectory%22+%2D+Day+3+%2D+Advent+of+Code+2020+%23AdventOfCode+https%3A%2F%2Fadventofcode%2Ecom%2F2020%2Fday%2F3'}else{return false;}" target="_blank">Mastodon</a
 162 ></span>]</span> this puzzle.</p>
 163 </main>
 164
 165 <!-- ga -->
 166 <script>
 167 (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
 168 (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
 169 m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
 170 })(window,document,'script','//www.google-analytics.com/analytics.js','ga');
 171 ga('create', 'UA-69522494-1', 'auto');
 172 ga('set', 'anonymizeIp', true);
 173 ga('send', 'pageview');
 174 </script>
 175 <!-- /ga -->
 176 </body>
 177 </html>