--- /dev/null
+import Data.List ((\\), nub, sortOn)
+import Numeric (showIntAtBase)
+import Data.Char (intToDigit)
+import Data.Bits (popCount)
+
+import qualified Data.Map.Lazy as Map -- day 4, 5
+
+type Pos = (Int, Int)
+
+seed = 1362
+
+goal1 = (31, 39)
+
+main :: IO ()
+main = do
+ part1
+ part2
+
+
+part1 :: IO ()
+part1 = print $ length $ tail $ extractJust $ aStar [[(1, 1)]] []
+
+part2 :: IO ()
+part2 = do print $ length $ tail $ edl 50 [[(1, 1)]] []
+ putStrLn $ showRoomR 30 25 $ edl 50 [[(1, 1)]] []
+-- part2 = print $ length $ tail $ edl 50 [[(1, 1)]] []
+
+
+extractJust :: Maybe [a] -> [a]
+extractJust Nothing = []
+extractJust (Just x) = x
+
+isWall :: Int -> Int -> Bool
+isWall x y = (popCount n) `mod` 2 == 1
+ where
+ n = x*x + 3*x + 2*x*y + y + y*y + seed
+
+
+showRoom w h = unlines rows
+ where
+ rows = [row x | x <- [0..h]]
+ row x = [showCell x y | y <- [0..w]]
+ showCell x y = if (isWall x y) then '#' else '.'
+
+showRoomR w h reached = unlines rows
+ where
+ rows = [row x | x <- [0..h]]
+ row x = [showCell x y | y <- [0..w]]
+ showCell x y = if (isWall x y)
+ then '#'
+ else if (x, y) `elem` reached
+ then 'O'
+ else '.'
+
+
+aStar :: [[Pos]] -> [Pos] -> Maybe [Pos]
+aStar [] _ = Nothing
+aStar (currentTrail:trails) closed =
+ if isGoal (head currentTrail) then Just currentTrail
+ else if (head currentTrail) `elem` closed then aStar trails closed
+ else aStar newAgenda ((head currentTrail): closed)
+ where newAgenda =
+ sortOn (\a -> trailCost a) $
+ trails ++ (candidates currentTrail closed)
+ trailCost t = estimateCost (head t) + length t - 1
+
+
+-- exhaustive depth-limited
+edl :: Int -> [[Pos]] -> [Pos] -> [Pos]
+edl _ [] closed = nub closed
+edl limit (currentTrail:trails) closed =
+ if (length currentTrail) > (limit+1) then edl limit trails ((head currentTrail):closed)
+ else if (head currentTrail) `elem` closed then edl limit trails closed
+ else edl limit newAgenda ((head currentTrail):closed)
+ where newAgenda = trails ++ (candidates currentTrail closed)
+
+candidates :: [Pos] -> [Pos] -> [[Pos]]
+candidates currentTrail closed = newCandidates
+ where
+ (candidate:trail) = currentTrail
+ succs = legalSuccessors $ successors candidate
+ nonloops = (succs \\ trail) \\ closed
+ newCandidates = map (\n -> n:candidate:trail) nonloops
+
+isGoal :: Pos -> Bool
+isGoal p = p == goal1
+
+isLegal :: Pos -> Bool
+isLegal (x, y) =
+ x >= 0 && y >= 0 && (not $ isWall x y)
+
+successors :: Pos -> [Pos]
+successors (x, y) = [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]
+
+legalSuccessors :: [Pos] -> [Pos]
+legalSuccessors = filter (isLegal)
+
+estimateCost :: Pos -> Int
+estimateCost (x, y) = abs (x - gx) + abs (y - gy)
+ where (gx, gy) = goal1
+
--- /dev/null
+<!DOCTYPE html>
+<html lang="en-us">
+<head>
+<meta charset="utf-8"/>
+<title>Day 13 - 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?9"/>
+<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
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+-->
+<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">26*</span></div></div><div><h1 class="title-event"> <span class="title-event-wrap">λy.</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>
+
+<div id="sidebar">
+<div id="sponsor"><div class="quiet">Our <a href="/2016/sponsors">sponsors</a> help make AoC possible:</div><p><a href="https://www.detroitlabs.com/careers" target="_blank" onclick="if(ga)ga('send','event','sponsor','click',this.href);">Detroit Labs</a> - Build beautiful mobile apps.</p></div>
+<div id="ad">
+<script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
+<!-- Advent of Code Wide Skyscraper -->
+<ins class="adsbygoogle"
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+
+<main>
+<article class="day-desc"><h2>--- Day 13: A Maze of Twisty Little Cubicles ---</h2><p>You arrive at the first floor of this new building to discover a much less welcoming environment than the shiny atrium of the last one. Instead, you are in a maze of <span title="You are in a twisty alike of little cubicles, all maze.">twisty little cubicles</span>, all alike.</p>
+<p>Every location in this area is addressed by a pair of non-negative integers (<code>x,y</code>). Each such coordinate is either a wall or an open space. You can't move diagonally. The cube maze starts at <code>0,0</code> and seems to extend infinitely toward <em>positive</em> <code>x</code> and <code>y</code>; negative values are <em>invalid</em>, as they represent a location outside the building. You are in a small waiting area at <code>1,1</code>.</p>
+<p>While it seems chaotic, a nearby morale-boosting poster explains, the layout is actually quite logical. You can determine whether a given <code>x,y</code> coordinate will be a wall or an open space using a simple system:</p>
+<ul>
+<li>Find <code>x*x + 3*x + 2*x*y + y + y*y</code>.</li>
+<li>Add the office designer's favorite number (your puzzle input).</li>
+<li>Find the <a href="https://en.wikipedia.org/wiki/Binary_number">binary representation</a> of that sum; count the <em>number</em> of <a href="https://en.wikipedia.org/wiki/Bit">bits</a> that are <code>1</code>.
+<ul>
+<li>If the number of bits that are <code>1</code> is <em>even</em>, it's an <em>open space</em>.</li>
+<li>If the number of bits that are <code>1</code> is <em>odd</em>, it's a <em>wall</em>.</li>
+</ul>
+</li>
+</ul>
+<p>For example, if the office designer's favorite number were <code>10</code>, drawing walls as <code>#</code> and open spaces as <code>.</code>, the corner of the building containing <code>0,0</code> would look like this:</p>
+<pre><code> 0123456789
+0 .#.####.##
+1 ..#..#...#
+2 #....##...
+3 ###.#.###.
+4 .##..#..#.
+5 ..##....#.
+6 #...##.###
+</code></pre>
+<p>Now, suppose you wanted to reach <code>7,4</code>. The shortest route you could take is marked as <code>O</code>:</p>
+<pre><code> 0123456789
+0 .#.####.##
+1 .O#..#...#
+2 #OOO.##...
+3 ###O#.###.
+4 .##OO#OO#.
+5 ..##OOO.#.
+6 #...##.###
+</code></pre>
+<p>Thus, reaching <code>7,4</code> would take a minimum of <code>11</code> steps (starting from your current location, <code>1,1</code>).</p>
+<p>What is the <em>fewest number of steps required</em> for you to reach <code>31,39</code>?</p>
+</article>
+<p>Your puzzle answer was <code>82</code>.</p><article class="day-desc"><h2>--- Part Two ---</h2><p><em>How many locations</em> (distinct <code>x,y</code> coordinates, including your starting location) can you reach in at most <code>50</code> steps?</p>
+</article>
+<p>Your puzzle answer was <code>138</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">1362</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+%22A+Maze+of+Twisty+Little+Cubicles%22+%2D+Day+13+%2D+Advent+of+Code+2016&url=http%3A%2F%2Fadventofcode%2Ecom%2F2016%2Fday%2F13&related=ericwastl&hashtags=AdventOfCode" target="_blank">Twitter</a>
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+></span>]</span> this puzzle.</p>
+</main>
+
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