source /home/neil/.ghcup/env
```
+and then set the default GHC to use with `ghcup set ghc 9.0.1` .
+
Install [Haskell Language Server](https://haskell-language-server.readthedocs.io/en/latest/configuration.html) for Sublime Text
executable advent03
import: common-extensions, build-directives
main-is: advent03/Main.hs
+
+executable advent04
+ import: common-extensions, build-directives
+ main-is: advent04/Main.hs
+ build-depends: text, attoparsec
--- /dev/null
+import Data.Text ()
+import qualified Data.Text.IO as TIO
+
+import Data.Attoparsec.Text
+import Control.Applicative
+
+import Data.List
+
+type Square = [[Int]]
+type BingoSquare = [[BingoNum]]
+data BingoNum = BingoNum Int Bool
+ deriving (Eq, Show)
+data BingoState = BingoState Int [BingoSquare]
+ deriving (Eq, Show)
+
+
+
+main :: IO ()
+main =
+ do text <- TIO.readFile "data/advent04.txt"
+ let (nums, rawSquares) = successfulParse text
+ let squares = map mkSquare rawSquares
+ print $ part1 nums squares
+ print $ part2 nums squares
+
+part1 :: [Int] -> [BingoSquare] -> Int
+part1 callNums squares = finalCalled * winningSum
+ where allSteps = scanl' bingoStep (BingoState 0 squares) callNums
+ BingoState finalCalled finalSquares = head $ dropWhile (not . hasCompletedSquare) allSteps
+ winningSquare = head $ filter completed finalSquares
+ winningSum = unmarkedSum winningSquare
+
+part2 :: [Int] -> [BingoSquare] -> Int
+part2 callNums squares = finalCalled * winningSum
+ where allSteps = scanl' pruningBingoStep (BingoState 0 squares) callNums
+ BingoState finalCalled finalSquares =
+ head $ dropWhile (not . hasCompletedSquare)
+ $ dropWhile manyRemainingSquares allSteps
+ winningSquare = head finalSquares
+ winningSum = unmarkedSum winningSquare
+
+
+bingoStep :: BingoState -> Int -> BingoState
+bingoStep (BingoState _ squares) caller = BingoState caller squares'
+ where squares' = map (callSquare caller) squares
+
+pruningBingoStep :: BingoState -> Int -> BingoState
+pruningBingoStep (BingoState _ squares) caller = BingoState caller squares''
+ where squares' = filter (not . completed) squares
+ squares'' = map (callSquare caller) squares'
+
+hasCompletedSquare :: BingoState -> Bool
+hasCompletedSquare (BingoState _n squares) = any completed squares
+
+
+unmarkedSum :: BingoSquare -> Int
+unmarkedSum bingoSquare =
+ sum [value bn | r <- bingoSquare, bn <- r, (not $ isCalled bn)]
+
+manyRemainingSquares :: BingoState -> Bool
+manyRemainingSquares (BingoState _ squares) = (length squares) > 1
+
+
+mkBingoNum :: Int -> BingoNum
+mkBingoNum n = BingoNum n False
+
+forceCall :: BingoNum -> BingoNum
+forceCall (BingoNum n _) = BingoNum n True
+
+call :: Int -> BingoNum -> BingoNum
+call num (BingoNum target called)
+ | num == target = BingoNum target True
+ | otherwise = BingoNum target called
+
+isCalled :: BingoNum -> Bool
+isCalled (BingoNum _ c) = c
+
+value :: BingoNum -> Int
+value (BingoNum n _) = n
+
+mkSquare :: Square -> BingoSquare
+mkSquare = map (map mkBingoNum)
+
+callSquare :: Int -> BingoSquare -> BingoSquare
+callSquare n = map (map (call n))
+
+completed :: BingoSquare -> Bool
+completed sq = (any completedRow sq) || (any completedRow $ transpose sq)
+
+completedRow :: [BingoNum] -> Bool
+completedRow = all isCalled
+
+-- Parse the input file
+
+bingoP = (,) <$> calledP <*> (blankLines *> squaresP)
+
+calledP = decimal `sepBy` ","
+
+squaresP = squareP `sepBy` blankLines
+squareP = rowP `sepBy` endOfLine
+rowP = paddedDecimal `sepBy1` " "
+
+-- paddedDecimal :: Parser Text Int
+paddedDecimal = (many " ") *> decimal
+
+blankLines = many1 endOfLine
+
+-- successfulParse :: Text -> (Integer, [Maybe Integer])
+successfulParse input =
+ case parseOnly bingoP input of
+ Left _err -> ([], []) -- TIO.putStr $ T.pack $ parseErrorPretty err
+ Right bingo -> bingo
--- /dev/null
+93,49,16,88,4,92,23,38,44,98,97,8,5,69,41,70,19,11,29,40,90,43,79,96,68,10,31,35,34,32,0,67,83,33,2,76,24,87,99,77,82,66,12,15,28,59,64,95,91,71,62,22,53,46,39,81,75,86,74,56,50,18,17,73,13,54,60,48,21,51,52,55,85,80,30,36,47,3,26,57,84,25,63,27,37,94,7,45,58,9,78,65,72,6,14,61,20,1,42,89
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+
+62 45 2 46 90
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+
+72 63 57 95 16
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+
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+ 8 95 88 42 6
+
+ 4 37 62 80 10
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+
+61 45 93 95 91
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+
+91 59 26 69 61
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+
+94 50 23 64 46
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+
+89 97 86 21 4
+57 29 17 46 22
+25 10 49 74 63
+24 23 93 56 11
+37 48 82 55 88
\ No newline at end of file
--- /dev/null
+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
+
+22 13 17 11 0
+ 8 2 23 4 24
+21 9 14 16 7
+ 6 10 3 18 5
+ 1 12 20 15 19
+
+ 3 15 0 2 22
+ 9 18 13 17 5
+19 8 7 25 23
+20 11 10 24 4
+14 21 16 12 6
+
+14 21 17 24 4
+10 16 15 9 19
+18 8 23 26 20
+22 11 13 6 5
+ 2 0 12 3 7
\ No newline at end of file
--- /dev/null
+<!DOCTYPE html>
+<html lang="en-us">
+<head>
+<meta charset="utf-8"/>
+<title>Day 3 - Advent of Code 2021</title>
+<!--[if lt IE 9]><script src="/static/html5.js"></script><![endif]-->
+<link href='//fonts.googleapis.com/css?family=Source+Code+Pro:300&subset=latin,latin-ext' rel='stylesheet' type='text/css'/>
+<link rel="stylesheet" type="text/css" href="/static/style.css?26"/>
+<link rel="stylesheet alternate" type="text/css" href="/static/highcontrast.css?0" title="High Contrast"/>
+<link rel="shortcut icon" href="/favicon.png"/>
+</head><!--
+
+
+
+
+Oh, hello! Funny seeing you here.
+
+I appreciate your enthusiasm, but you aren't going to find much down here.
+There certainly aren't clues to any of the puzzles. The best surprises don't
+even appear in the source until you unlock them for real.
+
+Please be careful with automated requests; I'm not a massive company, and I can
+only take so much traffic. Please be considerate so that everyone gets to play.
+
+If you're curious about how Advent of Code works, it's running on some custom
+Perl code. Other than a few integrations (auth, analytics, social media), I
+built the whole thing myself, including the design, animations, prose, and all
+of the puzzles.
+
+The puzzles are most of the work; preparing a new calendar and a new set of
+puzzles each year takes all of my free time for 4-5 months. A lot of effort
+went into building this thing - I hope you're enjoying playing it as much as I
+enjoyed making it for you!
+
+If you'd like to hang out, I'm @ericwastl on Twitter.
+
+- Eric Wastl
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+-->
+<body>
+<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">6*</span></div></div><div><h1 class="title-event"> <span class="title-event-wrap">{:year </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>
+
+<div id="sidebar">
+<div id="sponsor"><div class="quiet">Our <a href="/2021/sponsors">sponsors</a> help make Advent of Code possible:</div><div class="sponsor"><a href="https://blog.scottlogic.com/category/tech.html" target="_blank" onclick="if(ga)ga('send','event','sponsor','sidebar',this.href);" rel="noopener">Scott Logic</a> - Check out our tech blog if you're interested in joining a smart, inclusive community. Have a great and safe Christmas!</div></div>
+</div><!--/sidebar-->
+
+<main>
+<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>
+<article class="day-desc"><h2>--- Day 3: Binary Diagnostic ---</h2><p>The submarine has been making some <span title="Turns out oceans are heavy.">odd creaking noises</span>, so you ask it to produce a diagnostic report just in case.</p>
+<p>The diagnostic report (your puzzle input) consists of a list of binary numbers which, when decoded properly, can tell you many useful things about the conditions of the submarine. The first parameter to check is the <em>power consumption</em>.</p>
+<p>You need to use the binary numbers in the diagnostic report to generate two new binary numbers (called the <em>gamma rate</em> and the <em>epsilon rate</em>). The power consumption can then be found by multiplying the gamma rate by the epsilon rate.</p>
+<p>Each bit in the gamma rate can be determined by finding the <em>most common bit in the corresponding position</em> of all numbers in the diagnostic report. For example, given the following diagnostic report:</p>
+<pre><code>00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010
+</code></pre>
+<p>Considering only the first bit of each number, there are five <code>0</code> bits and seven <code>1</code> bits. Since the most common bit is <code>1</code>, the first bit of the gamma rate is <code>1</code>.</p>
+<p>The most common second bit of the numbers in the diagnostic report is <code>0</code>, so the second bit of the gamma rate is <code>0</code>.</p>
+<p>The most common value of the third, fourth, and fifth bits are <code>1</code>, <code>1</code>, and <code>0</code>, respectively, and so the final three bits of the gamma rate are <code>110</code>.</p>
+<p>So, the gamma rate is the binary number <code>10110</code>, or <code><em>22</em></code> in decimal.</p>
+<p>The epsilon rate is calculated in a similar way; rather than use the most common bit, the least common bit from each position is used. So, the epsilon rate is <code>01001</code>, or <code><em>9</em></code> in decimal. Multiplying the gamma rate (<code>22</code>) by the epsilon rate (<code>9</code>) produces the power consumption, <code><em>198</em></code>.</p>
+<p>Use the binary numbers in your diagnostic report to calculate the gamma rate and epsilon rate, then multiply them together. <em>What is the power consumption of the submarine?</em> (Be sure to represent your answer in decimal, not binary.)</p>
+</article>
+<p>Your puzzle answer was <code>2724524</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>Next, you should verify the <em>life support rating</em>, which can be determined by multiplying the <em>oxygen generator rating</em> by the <em>CO2 scrubber rating</em>.</p>
+<p>Both the oxygen generator rating and the CO2 scrubber rating are values that can be found in your diagnostic report - finding them is the tricky part. Both values are located using a similar process that involves filtering out values until only one remains. Before searching for either rating value, start with the full list of binary numbers from your diagnostic report and <em>consider just the first bit</em> of those numbers. Then:</p>
+<ul>
+<li>Keep only numbers selected by the <em>bit criteria</em> for the type of rating value for which you are searching. Discard numbers which do not match the bit criteria.</li>
+<li>If you only have one number left, stop; this is the rating value for which you are searching.</li>
+<li>Otherwise, repeat the process, considering the next bit to the right.</li>
+</ul>
+<p>The <em>bit criteria</em> depends on which type of rating value you want to find:</p>
+<ul>
+<li>To find <em>oxygen generator rating</em>, determine the <em>most common</em> value (<code>0</code> or <code>1</code>) in the current bit position, and keep only numbers with that bit in that position. If <code>0</code> and <code>1</code> are equally common, keep values with a <code><em>1</em></code> in the position being considered.</li>
+<li>To find <em>CO2 scrubber rating</em>, determine the <em>least common</em> value (<code>0</code> or <code>1</code>) in the current bit position, and keep only numbers with that bit in that position. If <code>0</code> and <code>1</code> are equally common, keep values with a <code><em>0</em></code> in the position being considered.</li>
+</ul>
+<p>For example, to determine the <em>oxygen generator rating</em> value using the same example diagnostic report from above:</p>
+<ul>
+<li>Start with all 12 numbers and consider only the first bit of each number. There are more <code>1</code> bits (7) than <code>0</code> bits (5), so keep only the 7 numbers with a <code>1</code> in the first position: <code>11110</code>, <code>10110</code>, <code>10111</code>, <code>10101</code>, <code>11100</code>, <code>10000</code>, and <code>11001</code>.</li>
+<li>Then, consider the second bit of the 7 remaining numbers: there are more <code>0</code> bits (4) than <code>1</code> bits (3), so keep only the 4 numbers with a <code>0</code> in the second position: <code>10110</code>, <code>10111</code>, <code>10101</code>, and <code>10000</code>.</li>
+<li>In the third position, three of the four numbers have a <code>1</code>, so keep those three: <code>10110</code>, <code>10111</code>, and <code>10101</code>.</li>
+<li>In the fourth position, two of the three numbers have a <code>1</code>, so keep those two: <code>10110</code> and <code>10111</code>.</li>
+<li>In the fifth position, there are an equal number of <code>0</code> bits and <code>1</code> bits (one each). So, to find the <em>oxygen generator rating</em>, keep the number with a <code>1</code> in that position: <code>10111</code>.</li>
+<li>As there is only one number left, stop; the <em>oxygen generator rating</em> is <code>10111</code>, or <code><em>23</em></code> in decimal.</li>
+</ul>
+<p>Then, to determine the <em>CO2 scrubber rating</em> value from the same example above:</p>
+<ul>
+<li>Start again with all 12 numbers and consider only the first bit of each number. There are fewer <code>0</code> bits (5) than <code>1</code> bits (7), so keep only the 5 numbers with a <code>0</code> in the first position: <code>00100</code>, <code>01111</code>, <code>00111</code>, <code>00010</code>, and <code>01010</code>.</li>
+<li>Then, consider the second bit of the 5 remaining numbers: there are fewer <code>1</code> bits (2) than <code>0</code> bits (3), so keep only the 2 numbers with a <code>1</code> in the second position: <code>01111</code> and <code>01010</code>.</li>
+<li>In the third position, there are an equal number of <code>0</code> bits and <code>1</code> bits (one each). So, to find the <em>CO2 scrubber rating</em>, keep the number with a <code>0</code> in that position: <code>01010</code>.</li>
+<li>As there is only one number left, stop; the <em>CO2 scrubber rating</em> is <code>01010</code>, or <code><em>10</em></code> in decimal.</li>
+</ul>
+<p>Finally, to find the life support rating, multiply the oxygen generator rating (<code>23</code>) by the CO2 scrubber rating (<code>10</code>) to get <code><em>230</em></code>.</p>
+<p>Use the binary numbers in your diagnostic report to calculate the oxygen generator rating and CO2 scrubber rating, then multiply them together. <em>What is the life support rating of the submarine?</em> (Be sure to represent your answer in decimal, not binary.)</p>
+</article>
+<p>Your puzzle answer was <code>2775870</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
+<p>At this point, you should <a href="/2021">return to your Advent calendar</a> and try another puzzle.</p>
+<p>If you still want to see it, you can <a href="3/input" target="_blank">get your puzzle input</a>.</p>
+<p>You can also <span class="share">[Share<span class="share-content">on
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+></span>]</span> this puzzle.</p>
+</main>
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+<title>Day 4 - Advent of Code 2021</title>
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+I appreciate your enthusiasm, but you aren't going to find much down here.
+There certainly aren't clues to any of the puzzles. The best surprises don't
+even appear in the source until you unlock them for real.
+
+Please be careful with automated requests; I'm not a massive company, and I can
+only take so much traffic. Please be considerate so that everyone gets to play.
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+If you're curious about how Advent of Code works, it's running on some custom
+Perl code. Other than a few integrations (auth, analytics, social media), I
+built the whole thing myself, including the design, animations, prose, and all
+of the puzzles.
+
+The puzzles are most of the work; preparing a new calendar and a new set of
+puzzles each year takes all of my free time for 4-5 months. A lot of effort
+went into building this thing - I hope you're enjoying playing it as much as I
+enjoyed making it for you!
+
+If you'd like to hang out, I'm @ericwastl on Twitter.
+
+- Eric Wastl
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+<body>
+<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"> <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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+<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>
+<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>
+<p>Maybe it wants to play <a href="https://en.wikipedia.org/wiki/Bingo_(American_version)" target="_blank">bingo</a>?</p>
+<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>
+<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>
+<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
+
+22 13 17 11 0
+ 8 2 23 4 24
+21 9 14 16 7
+ 6 10 3 18 5
+ 1 12 20 15 19
+
+ 3 15 0 2 22
+ 9 18 13 17 5
+19 8 7 25 23
+20 11 10 24 4
+14 21 16 12 6
+
+14 21 17 24 4
+10 16 15 9 19
+18 8 23 26 20
+22 11 13 6 5
+ 2 0 12 3 7
+</code></pre>
+<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>
+<pre><code>22 13 17 <em>11</em> 0 3 15 0 2 22 14 21 17 24 <em>4</em>
+ 8 2 23 <em>4</em> 24 <em>9</em> 18 13 17 <em>5</em> 10 16 15 <em>9</em> 19
+21 <em>9</em> 14 16 <em>7</em> 19 8 <em>7</em> 25 23 18 8 23 26 20
+ 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>
+ 1 12 20 15 19 14 21 16 12 6 2 0 12 3 <em>7</em>
+</code></pre>
+<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>
+<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>
+ 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
+<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
+ 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>
+ 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>
+</code></pre>
+<p>Finally, <code>24</code> is drawn:</p>
+<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>
+ 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
+<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
+ 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>
+ 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>
+</code></pre>
+<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>
+<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>
+<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>
+</article>
+<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>
+<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>
+<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>
+<p>Figure out which board will win last. <em>Once it wins, what would its final score be?</em></p>
+</article>
+<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>
+<p>At this point, you should <a href="/2021">return to your Advent calendar</a> and try another puzzle.</p>
+<p>If you still want to see it, you can <a href="4/input" target="_blank">get your puzzle input</a>.</p>
+<p>You can also <span class="share">[Share<span class="share-content">on
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