problems/day04.html

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  16 Oh, hello!  Funny seeing you here.
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  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!
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  35 If you'd like to hang out, I'm @ericwastl on Twitter.
  36
  37 - Eric Wastl
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  90 <header><div><h1 class="title-global"><a href="/">Advent of Code</a></h1><nav><ul><li><a href="/2021/about">[About]</a></li><li><a href="/2021/events">[Events]</a></li><li><a href="https://teespring.com/stores/advent-of-code" target="_blank">[Shop]</a></li><li><a href="/2021/settings">[Settings]</a></li><li><a href="/2021/auth/logout">[Log Out]</a></li></ul></nav><div class="user">Neil Smith <a href="/2021/support" class="supporter-badge" title="Advent of Code Supporter">(AoC++)</a> <span class="star-count">8*</span></div></div><div><h1 class="title-event">&nbsp;&nbsp;&nbsp;<span class="title-event-wrap">sub y{</span><a href="/2021">2021</a><span class="title-event-wrap">}</span></h1><nav><ul><li><a href="/2021">[Calendar]</a></li><li><a href="/2021/support">[AoC++]</a></li><li><a href="/2021/sponsors">[Sponsors]</a></li><li><a href="/2021/leaderboard">[Leaderboard]</a></li><li><a href="/2021/stats">[Stats]</a></li></ul></nav></div></header>
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  98 <article class="day-desc"><h2>--- Day 4: Giant Squid ---</h2><p>You're already almost 1.5km (almost a mile) below the surface of the ocean, already so deep that you can't see any sunlight. What you <em>can</em> see, however, is a giant squid that has attached itself to the outside of your submarine.</p>
  99 <p>Maybe it wants to play <a href="https://en.wikipedia.org/wiki/Bingo_(American_version)" target="_blank">bingo</a>?</p>
 100 <p>Bingo is played on a set of boards each consisting of a 5x5 grid of numbers. Numbers are chosen at random, and the chosen number is <em>marked</em> on all boards on which it appears. (Numbers may not appear on all boards.) If all numbers in any row or any column of a board are marked, that board <em>wins</em>. (Diagonals don't count.)</p>
 101 <p>The submarine has a <em>bingo subsystem</em> to help passengers (currently, you and the giant squid) pass the time. It automatically generates a random order in which to draw numbers and a random set of boards (your puzzle input). For example:</p>
 102 <pre><code>7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
 103
 104 22 13 17 11  0
 105  8  2 23  4 24
 106 21  9 14 16  7
 107  6 10  3 18  5
 108  1 12 20 15 19
 109
 110  3 15  0  2 22
 111  9 18 13 17  5
 112 19  8  7 25 23
 113 20 11 10 24  4
 114 14 21 16 12  6
 115
 116 14 21 17 24  4
 117 10 16 15  9 19
 118 18  8 23 26 20
 119 22 11 13  6  5
 120  2  0 12  3  7
 121 </code></pre>
 122 <p>After the first five numbers are drawn (<code>7</code>, <code>4</code>, <code>9</code>, <code>5</code>, and <code>11</code>), there are no winners, but the boards are marked as follows (shown here adjacent to each other to save space):</p>
 123 <pre><code>22 13 17 <em>11</em>  0         3 15  0  2 22        14 21 17 24  <em>4</em>
 124  8  2 23  <em>4</em> 24         <em>9</em> 18 13 17  <em>5</em>        10 16 15  <em>9</em> 19
 125 21  <em>9</em> 14 16  <em>7</em>        19  8  <em>7</em> 25 23        18  8 23 26 20
 126  6 10  3 18  <em>5</em>        20 <em>11</em> 10 24  <em>4</em>        22 <em>11</em> 13  6  <em>5</em>
 127  1 12 20 15 19        14 21 16 12  6         2  0 12  3  <em>7</em>
 128 </code></pre>
 129 <p>After the next six numbers are drawn (<code>17</code>, <code>23</code>, <code>2</code>, <code>0</code>, <code>14</code>, and <code>21</code>), there are still no winners:</p>
 130 <pre><code>22 13 <em>17</em> <em>11</em>  <em>0</em>         3 15  <em>0</em>  <em>2</em> 22        <em>14</em> <em>21</em> <em>17</em> 24  <em>4</em>
 131  8  <em>2</em> <em>23</em>  <em>4</em> 24         <em>9</em> 18 13 <em>17</em>  <em>5</em>        10 16 15  <em>9</em> 19
 132 <em>21</em>  <em>9</em> <em>14</em> 16  <em>7</em>        19  8  <em>7</em> 25 <em>23</em>        18  8 <em>23</em> 26 20
 133  6 10  3 18  <em>5</em>        20 <em>11</em> 10 24  <em>4</em>        22 <em>11</em> 13  6  <em>5</em>
 134  1 12 20 15 19        <em>14</em> <em>21</em> 16 12  6         <em>2</em>  <em>0</em> 12  3  <em>7</em>
 135 </code></pre>
 136 <p>Finally, <code>24</code> is drawn:</p>
 137 <pre><code>22 13 <em>17</em> <em>11</em>  <em>0</em>         3 15  <em>0</em>  <em>2</em> 22        <em>14</em> <em>21</em> <em>17</em> <em>24</em>  <em>4</em>
 138  8  <em>2</em> <em>23</em>  <em>4</em> <em>24</em>         <em>9</em> 18 13 <em>17</em>  <em>5</em>        10 16 15  <em>9</em> 19
 139 <em>21</em>  <em>9</em> <em>14</em> 16  <em>7</em>        19  8  <em>7</em> 25 <em>23</em>        18  8 <em>23</em> 26 20
 140  6 10  3 18  <em>5</em>        20 <em>11</em> 10 <em>24</em>  <em>4</em>        22 <em>11</em> 13  6  <em>5</em>
 141  1 12 20 15 19        <em>14</em> <em>21</em> 16 12  6         <em>2</em>  <em>0</em> 12  3  <em>7</em>
 142 </code></pre>
 143 <p>At this point, the third board <em>wins</em> because it has at least one complete row or column of marked numbers (in this case, the entire top row is marked: <code><em>14 21 17 24  4</em></code>).</p>
 144 <p>The <em>score</em> of the winning board can now be calculated. Start by finding the <em>sum of all unmarked numbers</em> on that board; in this case, the sum is <code>188</code>. Then, multiply that sum by <em>the number that was just called</em> when the board won, <code>24</code>, to get the final score, <code>188 * 24 = <em>4512</em></code>.</p>
 145 <p>To guarantee victory against the giant squid, figure out which board will win first. <em>What will your final score be if you choose that board?</em></p>
 146 </article>
 147 <p>Your puzzle answer was <code>82440</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>On the other hand, it might be wise to try a different strategy: <span title="That's 'cuz a submarine don't pull things' antennas out of their sockets when they lose. Giant squid are known to do that.">let the giant squid win</span>.</p>
 148 <p>You aren't sure how many bingo boards a giant squid could play at once, so rather than waste time counting its arms, the safe thing to do is to <em>figure out which board will win last</em> and choose that one. That way, no matter which boards it picks, it will win for sure.</p>
 149 <p>In the above example, the second board is the last to win, which happens after <code>13</code> is eventually called and its middle column is completely marked. If you were to keep playing until this point, the second board would have a sum of unmarked numbers equal to <code>148</code> for a final score of <code>148 * 13 = <em>1924</em></code>.</p>
 150 <p>Figure out which board will win last. <em>Once it wins, what would its final score be?</em></p>
 151 </article>
 152 <p>Your puzzle answer was <code>20774</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
 153 <p>At this point, you should <a href="/2021">return to your Advent calendar</a> and try another puzzle.</p>
 154 <p>If you still want to see it, you can <a href="4/input" target="_blank">get your puzzle input</a>.</p>
 155 <p>You can also <span class="share">[Share<span class="share-content">on
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 158 ></span>]</span> this puzzle.</p>
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