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<!DOCTYPE html>
<html lang="en-us">
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<meta charset="utf-8"/>
<title>Day 8 - Advent of Code 2022</title>
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<style>article *[title]{border-bottom:1px dotted #ffff66;}</style><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>Your puzzle answer was <code>1816</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>Content with the amount of tree cover available, the Elves just need to know the best spot to build their tree house: they would like to be able to see a lot of <em>trees</em>.</p>
<p>To measure the viewing distance from a given tree, look up, down, left, and right from that tree; stop if you reach an edge or at the first tree that is the same height or taller than the tree under consideration. (If a tree is right on the edge, at least one of its viewing distances will be zero.)</p>
<p>The Elves don't care about distant trees taller than those found by the rules above; the proposed tree house has large <a href="https://en.wikipedia.org/wiki/Eaves" target="_blank">eaves</a> to keep it dry, so they wouldn't be able to see higher than the tree house anyway.</p>
<p>In the example above, consider the middle <code>5</code> in the second row:</p>
<pre><code>30373
25<em>5</em>12
65332
33549
35390
</code></pre>
<ul>
<li>Looking up, its view is not blocked; it can see <code><em>1</em></code> tree (of height <code>3</code>).</li>
<li>Looking left, its view is blocked immediately; it can see only <code><em>1</em></code> tree (of height <code>5</code>, right next to it).</li>
<li>Looking right, its view is not blocked; it can see <code><em>2</em></code> trees.</li>
<li>Looking down, its view is blocked eventually; it can see <code><em>2</em></code> trees (one of height <code>3</code>, then the tree of height <code>5</code> that blocks its view).</li>
</ul>
<p>A tree's <em>scenic score</em> is found by <em>multiplying together</em> its viewing distance in each of the four directions. For this tree, this is <code><em>4</em></code> (found by multiplying <code>1 * 1 * 2 * 2</code>).</p>
<p>However, you can do even better: consider the tree of height <code>5</code> in the middle of the fourth row:</p>
<pre><code>30373
25512
65332
33<em>5</em>49
35390
</code></pre>
<ul>
<li>Looking up, its view is blocked at <code><em>2</em></code> trees (by another tree with a height of <code>5</code>).</li>
<li>Looking left, its view is not blocked; it can see <code><em>2</em></code> trees.</li>
<li>Looking down, its view is also not blocked; it can see <code><em>1</em></code> tree.</li>
<li>Looking right, its view is blocked at <code><em>2</em></code> trees (by a massive tree of height <code>9</code>).</li>
</ul>
<p>This tree's scenic score is <code><em>8</em></code> (<code>2 * 2 * 1 * 2</code>); this is the ideal spot for the tree house.</p>
<p>Consider each tree on your map. <em>What is the highest scenic score possible for any tree?</em></p>
</article>
<p>Your puzzle answer was <code>383520</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
<p>At this point, all that is left is for you to <a href="/2022">admire your Advent calendar</a>.</p>
<p>If you still want to see it, you can <a href="8/input" target="_blank">get your puzzle input</a>.</p>
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