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<!DOCTYPE html> <html lang="en-us"> <head> <meta charset="utf-8"/> <title>Day 8 - Advent of Code 2022</title> <link rel="stylesheet" type="text/css" href="/static/style.css?31"/> <link rel="stylesheet alternate" type="text/css" href="/static/highcontrast.css?1" title="High Contrast"/> <link rel="shortcut icon" href="/favicon.png"/> <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> </head> <body> <header><div><h1 class="title-global"><a href="/">Advent of Code</a></h1><nav><ul><li><a href="/2022/about">[About]</a></li><li><a href="/2022/events">[Events]</a></li><li><a href="https://teespring.com/stores/advent-of-code" target="_blank">[Shop]</a></li><li><a href="/2022/auth/login">[Log In]</a></li></ul></nav></div><div><h1 class="title-event">   <span class="title-event-wrap">int y=</span><a href="/2022">2022</a><span class="title-event-wrap">;</span></h1><nav><ul><li><a href="/2022">[Calendar]</a></li><li><a href="/2022/support">[AoC++]</a></li><li><a href="/2022/sponsors">[Sponsors]</a></li><li><a href="/2022/leaderboard">[Leaderboard]</a></li><li><a href="/2022/stats">[Stats]</a></li></ul></nav></div></header> <div id="sidebar"> <div id="sponsor"><div class="quiet">Our <a href="/2022/sponsors">sponsors</a> help make Advent of Code possible:</div><div class="sponsor"><a href="https://sentry.io/" target="_blank" onclick="if(ga)ga('send','event','sponsor','sidebar',this.href);" rel="noopener">Sentry.io</a> - More than 3.5 million developers across 85,000 organizations ship better software, faster, with Sentry. What are you waiting for?</div></div> </div> <main> <article class="day-desc"><h2>--- Day 8: Treetop Tree House ---</h2><p>The expedition comes across a peculiar patch of tall trees all planted carefully in a grid. The Elves explain that a previous expedition planted these trees as a reforestation effort. Now, they're curious if this would be a good location for a <a href="https://en.wikipedia.org/wiki/Tree_house" target="_blank">tree house</a>.</p> <p>First, determine whether there is enough tree cover here to keep a tree house <em>hidden</em>. To do this, you need to count the number of trees that are <em>visible from outside the grid</em> when looking directly along a row or column.</p> <p>The Elves have already launched a <a href="https://en.wikipedia.org/wiki/Quadcopter" target="_blank">quadcopter</a> to generate a map with the height of each tree (<span title="The Elves have already launched a quadcopter (your puzzle input).">your puzzle input</span>). For example:</p> <pre><code>30373 25512 65332 33549 35390 </code></pre> <p>Each tree is represented as a single digit whose value is its height, where <code>0</code> is the shortest and <code>9</code> is the tallest.</p> <p>A tree is <em>visible</em> if all of the other trees between it and an edge of the grid are <em>shorter</em> than it. Only consider trees in the same row or column; that is, only look up, down, left, or right from any given tree.</p> <p>All of the trees around the edge of the grid are <em>visible</em> - since they are already on the edge, there are no trees to block the view. In this example, that only leaves the <em>interior nine trees</em> to consider:</p> <ul> <li>The top-left <code>5</code> is <em>visible</em> from the left and top. (It isn't visible from the right or bottom since other trees of height <code>5</code> are in the way.)</li> <li>The top-middle <code>5</code> is <em>visible</em> from the top and right.</li> <li>The top-right <code>1</code> is not visible from any direction; for it to be visible, there would need to only be trees of height <em>0</em> between it and an edge.</li> <li>The left-middle <code>5</code> is <em>visible</em>, but only from the right.</li> <li>The center <code>3</code> is not visible from any direction; for it to be visible, there would need to be only trees of at most height <code>2</code> between it and an edge.</li> <li>The right-middle <code>3</code> is <em>visible</em> from the right.</li> <li>In the bottom row, the middle <code>5</code> is <em>visible</em>, but the <code>3</code> and <code>4</code> are not.</li> </ul> <p>With 16 trees visible on the edge and another 5 visible in the interior, a total of <code><em>21</em></code> trees are visible in this arrangement.</p> <p>Consider your map; <em>how many trees are visible from outside the grid?</em></p> </article> <p>To play, please identify yourself via one of these services:</p> <p><a href="/auth/github">[GitHub]</a> <a href="/auth/google">[Google]</a> <a href="/auth/twitter">[Twitter]</a> <a href="/auth/reddit">[Reddit]</a> <span class="quiet">- <a href="/about#faq_auth">[How Does Auth Work?]</a></span></p> </main>  <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','//www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-69522494-1', 'auto'); ga('set', 'anonymizeIp', true); ga('send', 'pageview'); </script>  </body> </html>