problems/day07.html

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  91 <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/settings">[Settings]</a></li><li><a href="/2022/auth/logout">[Log Out]</a></li></ul></nav><div class="user">Neil Smith <a href="/2022/support" class="supporter-badge" title="Advent of Code Supporter">(AoC++)</a> <span class="star-count">14*</span></div></div><div><h1 class="title-event">&nbsp;&nbsp;&nbsp;<span class="title-event-wrap">0xffff&amp;</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>
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  98 <article class="day-desc"><h2>--- Day 7: No Space Left On Device ---</h2><p>You can hear birds chirping and raindrops hitting leaves as the expedition proceeds. Occasionally, you can even hear much louder sounds in the distance; how big do the animals get out here, anyway?</p>
  99 <p>The device the Elves gave you has problems with more than just its communication system. You try to run a system update:</p>
 100 <pre><code>$ system-update --please --pretty-please-with-sugar-on-top
 101 <span title="E099 PROGRAMMER IS OVERLY POLITE">Error</span>: No space left on device
 102 </code></pre>
 103 <p>Perhaps you can delete some files to make space for the update?</p>
 104 <p>You browse around the filesystem to assess the situation and save the resulting terminal output (your puzzle input). For example:</p>
 105 <pre><code>$ cd /
 106 $ ls
 107 dir a
 108 14848514 b.txt
 109 8504156 c.dat
 110 dir d
 111 $ cd a
 112 $ ls
 113 dir e
 114 29116 f
 115 2557 g
 116 62596 h.lst
 117 $ cd e
 118 $ ls
 119 584 i
 120 $ cd ..
 121 $ cd ..
 122 $ cd d
 123 $ ls
 124 4060174 j
 125 8033020 d.log
 126 5626152 d.ext
 127 7214296 k
 128 </code></pre>
 129 <p>The filesystem consists of a tree of files (plain data) and directories (which can contain other directories or files). The outermost directory is called <code>/</code>. You can navigate around the filesystem, moving into or out of directories and listing the contents of the directory you're currently in.</p>
 130 <p>Within the terminal output, lines that begin with <code>$</code> are <em>commands you executed</em>, very much like some modern computers:</p>
 131 <ul>
 132 <li><code>cd</code> means <em>change directory</em>. This changes which directory is the current directory, but the specific result depends on the argument:
 133   <ul>
 134   <li><code>cd x</code> moves <em>in</em> one level: it looks in the current directory for the directory named <code>x</code> and makes it the current directory.</li>
 135   <li><code>cd ..</code> moves <em>out</em> one level: it finds the directory that contains the current directory, then makes that directory the current directory.</li>
 136   <li><code>cd /</code> switches the current directory to the outermost directory, <code>/</code>.</li>
 137   </ul>
 138 </li>
 139 <li><code>ls</code> means <em>list</em>. It prints out all of the files and directories immediately contained by the current directory:
 140   <ul>
 141   <li><code>123 abc</code> means that the current directory contains a file named <code>abc</code> with size <code>123</code>.</li>
 142   <li><code>dir xyz</code> means that the current directory contains a directory named <code>xyz</code>.</li>
 143   </ul>
 144 </li>
 145 </ul>
 146 <p>Given the commands and output in the example above, you can determine that the filesystem looks visually like this:</p>
 147 <pre><code>- / (dir)
 148   - a (dir)
 149     - e (dir)
 150       - i (file, size=584)
 151     - f (file, size=29116)
 152     - g (file, size=2557)
 153     - h.lst (file, size=62596)
 154   - b.txt (file, size=14848514)
 155   - c.dat (file, size=8504156)
 156   - d (dir)
 157     - j (file, size=4060174)
 158     - d.log (file, size=8033020)
 159     - d.ext (file, size=5626152)
 160     - k (file, size=7214296)
 161 </code></pre>
 162 <p>Here, there are four directories: <code>/</code> (the outermost directory), <code>a</code> and <code>d</code> (which are in <code>/</code>), and <code>e</code> (which is in <code>a</code>). These directories also contain files of various sizes.</p>
 163 <p>Since the disk is full, your first step should probably be to find directories that are good candidates for deletion. To do this, you need to determine the <em>total size</em> of each directory. The total size of a directory is the sum of the sizes of the files it contains, directly or indirectly. (Directories themselves do not count as having any intrinsic size.)</p>
 164 <p>The total sizes of the directories above can be found as follows:</p>
 165 <ul>
 166 <li>The total size of directory <code>e</code> is <em>584</em> because it contains a single file <code>i</code> of size 584 and no other directories.</li>
 167 <li>The directory <code>a</code> has total size <em>94853</em> because it contains files <code>f</code> (size 29116), <code>g</code> (size 2557), and <code>h.lst</code> (size 62596), plus file <code>i</code> indirectly (<code>a</code> contains <code>e</code> which contains <code>i</code>).</li>
 168 <li>Directory <code>d</code> has total size <em>24933642</em>.</li>
 169 <li>As the outermost directory, <code>/</code> contains every file. Its total size is <em>48381165</em>, the sum of the size of every file.</li>
 170 </ul>
 171 <p>To begin, find all of the directories with a total size of <em>at most 100000</em>, then calculate the sum of their total sizes. In the example above, these directories are <code>a</code> and <code>e</code>; the sum of their total sizes is <code><em>95437</em></code> (94853 + 584). (As in this example, this process can count files more than once!)</p>
 172 <p>Find all of the directories with a total size of at most 100000. <em>What is the sum of the total sizes of those directories?</em></p>
 173 </article>
 174 <p>Your puzzle answer was <code>1084134</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>Now, you're ready to choose a directory to delete.</p>
 175 <p>The total disk space available to the filesystem is <code><em>70000000</em></code>. To run the update, you need unused space of at least <code><em>30000000</em></code>. You need to find a directory you can delete that will <em>free up enough space</em> to run the update.</p>
 176 <p>In the example above, the total size of the outermost directory (and thus the total amount of used space) is <code>48381165</code>; this means that the size of the <em>unused</em> space must currently be <code>21618835</code>, which isn't quite the <code>30000000</code> required by the update. Therefore, the update still requires a directory with total size of at least <code>8381165</code> to be deleted before it can run.</p>
 177 <p>To achieve this, you have the following options:</p>
 178 <ul>
 179 <li>Delete directory <code>e</code>, which would increase unused space by <code>584</code>.</li>
 180 <li>Delete directory <code>a</code>, which would increase unused space by <code>94853</code>.</li>
 181 <li>Delete directory <code>d</code>, which would increase unused space by <code>24933642</code>.</li>
 182 <li>Delete directory <code>/</code>, which would increase unused space by <code>48381165</code>.</li>
 183 </ul>
 184 <p>Directories <code>e</code> and <code>a</code> are both too small; deleting them would not free up enough space. However, directories <code>d</code> and <code>/</code> are both big enough! Between these, choose the <em>smallest</em>: <code>d</code>, increasing unused space by <code><em>24933642</em></code>.</p>
 185 <p>Find the smallest directory that, if deleted, would free up enough space on the filesystem to run the update. <em>What is the total size of that directory?</em></p>
 186 </article>
 187 <p>Your puzzle answer was <code>6183184</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
 188 <p>At this point, you should <a href="/2022">return to your Advent calendar</a> and try another puzzle.</p>
 189 <p>If you still want to see it, you can <a href="7/input" target="_blank">get your puzzle input</a>.</p>
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