--- /dev/null
+module Main(main) where
+
+import Data.Hash.MD5 (md5s, Str(..))
+import Data.List (isPrefixOf)
+import qualified Data.Map.Lazy as Map
+
+type Password = Map.Map Integer Char
+
+input = "cxdnnyjw"
+
+main :: IO ()
+main = do
+ part1
+ part2
+
+
+part1 :: IO ()
+part1 = do
+ print $ take 8 [h!!5 | h <- filter (interesting) $ md5sequence input 0]
+
+part2 :: IO ()
+part2 = do
+ print $ Map.foldr (:) [] password
+ where interestingHashes =
+ [(read [h!!5], h!!6) |
+ h <- filter (interesting) (md5sequence input 0),
+ h!!5 `elem` "01234567"]
+ password = findPassword Map.empty interestingHashes
+
+
+md5sequence :: String -> Integer -> [String]
+md5sequence key i = (md5s (Str (key ++ show i))) : (md5sequence key (i+1))
+
+interesting :: String -> Bool
+interesting hash = "00000" `isPrefixOf` hash
+
+dontReplace :: (Integer, Char) -> Password -> Password
+dontReplace (k, v) = Map.insertWith (\_ v -> v) k v
+
+findPassword :: Password -> [(Integer, Char)] -> Password
+findPassword p (candidate:candidates)
+ | Map.size p == 8 = p
+ | otherwise = findPassword p' candidates
+ where p' = dontReplace candidate p
--- /dev/null
+<!DOCTYPE html>
+<html lang="en-us">
+<head>
+<meta charset="utf-8"/>
+<title>Day 5 - Advent of Code 2016</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?7"/>
+<link rel="shortcut icon" href="/favicon.ico?2"/>
+</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 Google, 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, ads, social media),
+I built the whole thing myself, including the design, animations, prose, and
+all of the puzzles.
+
+The puzzles probably took the longest; the easiest ones were around 45 minutes
+each, but the harder ones took 2-3 hours, and a few even longer than that. 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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+
+
+
+
+
+
+-->
+<body>
+<header><div><h1 class="title-global"><a href="/">Advent of Code</a></h1><nav><ul><li><a href="/2016/about">[About]</a></li><li><a href="/2016/support">[AoC++]</a></li><li><a href="/2016/events">[Events]</a></li><li><a href="/2016/settings">[Settings]</a></li><li><a href="/2016/auth/logout">[Log Out]</a></li></ul></nav><div class="user">Neil Smith <span class="supporter">(AoC++)</span> <span class="star-count">10*</span></div></div><div><h1 class="title-event"> <span class="title-event-wrap">y(</span><a href="/2016">2016</a><span class="title-event-wrap">)</span></h1><nav><ul><li><a href="/2016">[Calendar]</a></li><li><a href="/2016/leaderboard">[Leaderboard]</a></li><li><a href="/2016/stats">[Stats]</a></li><li><a href="/2016/sponsors">[Sponsors]</a></li></ul></nav></div></header>
+
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+<div id="sponsor"><div class="quiet">Our <a href="/2016/sponsors">sponsors</a> help make AoC possible:</div><p><a href="http://www.novetta.com/careers/#opportunities" target="_blank" onclick="if(ga)ga('send','event','sponsor','click',this.href);">Novetta</a> - Unleash your imagination. Innovate at Novetta.</p></div>
+<div id="ad">
+<script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
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+<ins class="adsbygoogle"
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+</div><!--/ad-->
+</div><!--/sidebar-->
+
+<main>
+<article class="day-desc"><h2>--- Day 5: How About a Nice Game of Chess? ---</h2><p>You are faced with a security door designed by Easter Bunny engineers that seem to have acquired most of their security knowledge by watching <a href="https://en.wikipedia.org/wiki/Hackers_(film)">hacking</a> <a href="https://en.wikipedia.org/wiki/WarGames">movies</a>.</p>
+<p>The <em>eight-character password</em> for the door is generated one character at a time by finding the <a href="https://en.wikipedia.org/wiki/MD5">MD5</a> hash of some Door ID (your puzzle input) and an increasing integer index (starting with <code>0</code>).</p>
+<p>A hash indicates the <em>next character</em> in the password if its <a href="https://en.wikipedia.org/wiki/Hexadecimal">hexadecimal</a> representation starts with <em>five zeroes</em>. If it does, the sixth character in the hash is the next character of the password.</p>
+<p>For example, if the Door ID is <code>abc</code>:</p>
+<ul>
+<li>The first index which produces a hash that starts with five zeroes is <code>3231929</code>, which we find by hashing <code>abc3231929</code>; the sixth character of the hash, and thus the first character of the password, is <code>1</code>.</li>
+<li><code>5017308</code> produces the next interesting hash, which starts with <code>000008f82...</code>, so the second character of the password is <code>8</code>.</li>
+<li>The third time a hash starts with five zeroes is for <code>abc5278568</code>, discovering the character <code>f</code>.</li>
+</ul>
+<p>In this example, after continuing this search a total of eight times, the password is <code>18f47a30</code>.</p>
+<p>Given the actual Door ID, <em>what is the password</em>?</p>
+</article>
+<p>Your puzzle answer was <code>f77a0e6e</code>.</p><article class="day-desc"><h2>--- Part Two ---</h2><p>As the door slides open, you are presented with a second door that uses a slightly more <span title="This one says 'WOPR' in block letters.">inspired</span> security mechanism. Clearly unimpressed by the last version (in what movie is the password decrypted <em>in order</em>?!), the Easter Bunny engineers have worked out <a href="https://www.youtube.com/watch?v=NHWjlCaIrQo&t=25">a better solution</a>.</p>
+<p>Instead of simply filling in the password from left to right, the hash now also indicates the <em>position</em> within the password to fill. You still look for hashes that begin with five zeroes; however, now, the <em>sixth</em> character represents the <em>position</em> (<code>0</code>-<code>7</code>), and the <em>seventh</em> character is the character to put in that position.</p>
+<p>A hash result of <code>000001f</code> means that <code>f</code> is the <em>second</em> character in the password. Use only the <em>first result</em> for each position, and ignore invalid positions.</p>
+<p>For example, if the Door ID is <code>abc</code>:</p>
+<ul>
+<li>The first interesting hash is from <code>abc3231929</code>, which produces <code>0000015...</code>; so, <code>5</code> goes in position <code>1</code>: <code>_5______</code>.</li>
+<li>In the previous method, <code>5017308</code> produced an interesting hash; however, it is ignored, because it specifies an invalid position (<code>8</code>).</li>
+<li>The second interesting hash is at index <code>5357525</code>, which produces <code>000004e...</code>; so, <code>e</code> goes in position <code>4</code>: <code>_5__e___</code>.</li>
+</ul>
+<p>You almost choke on your popcorn as the final character falls into place, producing the password <code>05ace8e3</code>.</p>
+<p>Given the actual Door ID and this new method, <em>what is the password</em>? Be extra proud of your solution if it uses a cinematic "decrypting" animation.</p>
+</article>
+<p>Your puzzle answer was <code>999828ec</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="/2016">return to your advent calendar</a> and try another puzzle.</p>
+<p>Your puzzle input was <code class="puzzle-input">cxdnnyjw</code>.</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+%22How+About+a+Nice+Game+of+Chess%3F%22+%2D+Day+5+%2D+Advent+of+Code+2016&url=http%3A%2F%2Fadventofcode%2Ecom%2F2016%2Fday%2F5&related=ericwastl&hashtags=AdventOfCode" target="_blank">Twitter</a>
+ <a href="https://plus.google.com/share?url=http%3A%2F%2Fadventofcode%2Ecom%2F2016%2Fday%2F5" target="_blank">Google+</a>
+ <a href="http://www.reddit.com/submit?url=http%3A%2F%2Fadventofcode%2Ecom%2F2016%2Fday%2F5&title=I%27ve+completed+%22How+About+a+Nice+Game+of+Chess%3F%22+%2D+Day+5+%2D+Advent+of+Code+2016" target="_blank">Reddit</a
+></span>]</span> this puzzle.</p>
+</main>
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