--- /dev/null
+-- Writeup at https://work.njae.me.uk/2022/12/21/advent-of-code-2022-day-20/
+
+import Debug.Trace
+
+import AoC
+import Data.List
+import Data.Maybe
+import Data.CircularList
+import Control.Lens
+
+data IndexedElem = IndexedElem { _idx :: Int, _shift :: Int, _value :: Int}
+ deriving (Show, Eq, Ord)
+makeLenses ''IndexedElem
+
+type MixList = CList IndexedElem
+
+key :: Int
+key = 811589153
+
+main :: IO ()
+main =
+ do dataFileName <- getDataFileName
+ text <- readFile dataFileName
+ let mixlist = successfulParse text
+ -- print mixlist
+ print $ part1 mixlist
+ print $ part2 mixlist
+
+part1, part2 :: [IndexedElem] -> Int
+part1 mixlist = findGrove $ mixRound $ fromList mixlist
+
+part2 mixlist = findGrove $ (!!10) $ iterate mixRound cMixlist
+ where cMixlist = fromList $ fmap scaleElem mixlist
+ scaleElem e = e & value %~ (* key) & shift .~ (((e ^. value) * key) `mod` (scale - 1))
+ scale = length mixlist
+
+mixRound :: MixList -> MixList
+mixRound mixlist = foldl' mixOne mixlist [1..(size mixlist)]
+
+mixOne :: MixList -> Int -> MixList
+mixOne mixlist elemIndex = insertL element $ rotN (element ^. shift) $ removeL elementFocused
+ where elementFocused = fromJust $ findRotateTo (\e -> e ^. idx == elemIndex) mixlist
+ element = fromJust $ focus elementFocused
+
+findGrove :: MixList -> Int
+findGrove mixlist = focus1 + focus2 + focus3
+ where mixlist0 = fromJust $ findRotateTo (\ep -> ep ^. value == 0) mixlist
+ focus1 = (fromJust $ focus $ rotN 1000 mixlist0) ^. value
+ focus2 = (fromJust $ focus $ rotN 2000 mixlist0) ^. value
+ focus3 = (fromJust $ focus $ rotN 3000 mixlist0) ^. value
+
+successfulParse :: String -> [IndexedElem]
+successfulParse text = fmap mkElem $ zip [1..] tns
+ where tns = fmap read $ lines text
+ mkElem (i, n) =
+ IndexedElem {_idx = i, _value = n,
+ _shift = n `mod` (l - 1) }
+ l = length tns
--- /dev/null
+<!DOCTYPE html>
+<html lang="en-us">
+<head>
+<meta charset="utf-8"/>
+<title>Day 20 - Advent of Code 2022</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'/>
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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>
+</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
+
+
+
+
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+
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+
+
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+
+
+
+
+
+
+-->
+<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/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">40*</span></div></div><div><h1 class="title-event"> <span class="title-event-wrap">0.0.0.0:</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://www.accenture.com/us-en/industries/afs-index" target="_blank" onclick="if(ga)ga('send','event','sponsor','sidebar',this.href);" rel="noopener">Accenture Federal Services</a> - Technology & ingenuity moving missions forward – come solve problems with us. Hiring software engineers, developers, and more now. Refer someone to earn up to $20K.</div></div>
+</div><!--/sidebar-->
+
+<main>
+<article class="day-desc"><h2>--- Day 20: Grove Positioning System ---</h2><p>It's finally time to meet back up with the Elves. When you try to contact them, however, you get no reply. Perhaps you're out of range?</p>
+<p>You know they're headed to the grove where the <em class="star">star</em> fruit grows, so if you can figure out where that is, you should be able to meet back up with them.</p>
+<p>Fortunately, your handheld device has a file (your puzzle input) that contains the grove's coordinates! Unfortunately, the file is <em>encrypted</em> - just in case the device were to fall into the wrong hands.</p>
+<p>Maybe you can <span title="You once again make a mental note to remind the Elves later not to invent their own cryptographic functions.">decrypt</span> it?</p>
+<p>When you were still back at the camp, you overheard some Elves talking about coordinate file encryption. The main operation involved in decrypting the file is called <em>mixing</em>.</p>
+<p>The encrypted file is a list of numbers. To <em>mix</em> the file, move each number forward or backward in the file a number of positions equal to the value of the number being moved. The list is <em>circular</em>, so moving a number off one end of the list wraps back around to the other end as if the ends were connected.</p>
+<p>For example, to move the <code>1</code> in a sequence like <code>4, 5, 6, <em>1</em>, 7, 8, 9</code>, the <code>1</code> moves one position forward: <code>4, 5, 6, 7, <em>1</em>, 8, 9</code>. To move the <code>-2</code> in a sequence like <code>4, <em>-2</em>, 5, 6, 7, 8, 9</code>, the <code>-2</code> moves two positions backward, wrapping around: <code>4, 5, 6, 7, 8, <em>-2</em>, 9</code>.</p>
+<p>The numbers should be moved <em>in the order they originally appear</em> in the encrypted file. Numbers moving around during the mixing process do not change the order in which the numbers are moved.</p>
+<p>Consider this encrypted file:</p>
+<pre><code>1
+2
+-3
+3
+-2
+0
+4
+</code></pre>
+<p>Mixing this file proceeds as follows:</p>
+<pre><code>Initial arrangement:
+1, 2, -3, 3, -2, 0, 4
+
+1 moves between 2 and -3:
+2, 1, -3, 3, -2, 0, 4
+
+2 moves between -3 and 3:
+1, -3, 2, 3, -2, 0, 4
+
+-3 moves between -2 and 0:
+1, 2, 3, -2, -3, 0, 4
+
+3 moves between 0 and 4:
+1, 2, -2, -3, 0, 3, 4
+
+-2 moves between 4 and 1:
+1, 2, -3, 0, 3, 4, -2
+
+0 does not move:
+1, 2, -3, 0, 3, 4, -2
+
+4 moves between -3 and 0:
+1, 2, -3, 4, 0, 3, -2
+</code></pre>
+<p>Then, the grove coordinates can be found by looking at the 1000th, 2000th, and 3000th numbers after the value <code>0</code>, wrapping around the list as necessary. In the above example, the 1000th number after <code>0</code> is <code><em>4</em></code>, the 2000th is <code><em>-3</em></code>, and the 3000th is <code><em>2</em></code>; adding these together produces <code><em>3</em></code>.</p>
+<p>Mix your encrypted file exactly once. <em>What is the sum of the three numbers that form the grove coordinates?</em></p>
+</article>
+<p>Your puzzle answer was <code>8721</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>The grove coordinate values seem nonsensical. While you ponder the mysteries of Elf encryption, you suddenly remember the rest of the decryption routine you overheard back at camp.</p>
+<p>First, you need to apply the <em>decryption key</em>, <code>811589153</code>. Multiply each number by the decryption key before you begin; this will produce the actual list of numbers to mix.</p>
+<p>Second, you need to mix the list of numbers <em>ten times</em>. The order in which the numbers are mixed does not change during mixing; the numbers are still moved in the order they appeared in the original, pre-mixed list. (So, if -3 appears fourth in the original list of numbers to mix, -3 will be the fourth number to move during each round of mixing.)</p>
+<p>Using the same example as above:</p>
+<pre><code>Initial arrangement:
+811589153, 1623178306, -2434767459, 2434767459, -1623178306, 0, 3246356612
+
+After 1 round of mixing:
+0, -2434767459, 3246356612, -1623178306, 2434767459, 1623178306, 811589153
+
+After 2 rounds of mixing:
+0, 2434767459, 1623178306, 3246356612, -2434767459, -1623178306, 811589153
+
+After 3 rounds of mixing:
+0, 811589153, 2434767459, 3246356612, 1623178306, -1623178306, -2434767459
+
+After 4 rounds of mixing:
+0, 1623178306, -2434767459, 811589153, 2434767459, 3246356612, -1623178306
+
+After 5 rounds of mixing:
+0, 811589153, -1623178306, 1623178306, -2434767459, 3246356612, 2434767459
+
+After 6 rounds of mixing:
+0, 811589153, -1623178306, 3246356612, -2434767459, 1623178306, 2434767459
+
+After 7 rounds of mixing:
+0, -2434767459, 2434767459, 1623178306, -1623178306, 811589153, 3246356612
+
+After 8 rounds of mixing:
+0, 1623178306, 3246356612, 811589153, -2434767459, 2434767459, -1623178306
+
+After 9 rounds of mixing:
+0, 811589153, 1623178306, -2434767459, 3246356612, 2434767459, -1623178306
+
+After 10 rounds of mixing:
+0, -2434767459, 1623178306, 3246356612, -1623178306, 2434767459, 811589153
+</code></pre>
+<p>The grove coordinates can still be found in the same way. Here, the 1000th number after <code>0</code> is <code><em>811589153</em></code>, the 2000th is <code><em>2434767459</em></code>, and the 3000th is <code><em>-1623178306</em></code>; adding these together produces <code><em>1623178306</em></code>.</p>
+<p>Apply the decryption key and mix your encrypted file ten times. <em>What is the sum of the three numbers that form the grove coordinates?</em></p>
+</article>
+<p>Your puzzle answer was <code>831878881825</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="/2022">return to your Advent calendar</a> and try another puzzle.</p>
+<p>If you still want to see it, you can <a href="20/input" target="_blank">get your puzzle input</a>.</p>
+<p>You can also <span class="share">[Share<span class="share-content">on
+ <a href="https://twitter.com/intent/tweet?text=I%27ve+completed+%22Grove+Positioning+System%22+%2D+Day+20+%2D+Advent+of+Code+2022&url=https%3A%2F%2Fadventofcode%2Ecom%2F2022%2Fday%2F20&related=ericwastl&hashtags=AdventOfCode" target="_blank">Twitter</a>
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