From 5ef88a61e55d7103553fa6b81df5e2a46009c204 Mon Sep 17 00:00:00 2001
From: Yuchen Pei <me@ypei.me>
Date: Mon, 11 Dec 2017 16:38:28 +0100
Subject: finished Day 10

---
 Puzzle10.hs | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

(limited to 'Puzzle10.hs')

diff --git a/Puzzle10.hs b/Puzzle10.hs
index 4909eac..fc01499 100644
--- a/Puzzle10.hs
+++ b/Puzzle10.hs
@@ -1,4 +1,7 @@
 import Data.List.Split (splitOn)
+import Data.Bits (xor)
+import Numeric (showHex)
+import Data.Char (ord)
 
 split3Ways :: [Int] -> Int -> Int -> ([Int], [Int], [Int])
 split3Ways xs from to
@@ -28,4 +31,22 @@ parseInput = (fmap read) . (splitOn ",")
 solve1 :: [Char] -> Int
 solve1 = solve1' . parseInput
 
+sparseHash :: [Int] -> [Int]
+sparseHash xs = let (ys, _, _) = foldl step ([0 .. 255], 0, 0) $ take (64 * (length xs)) (cycle xs) in ys
+
+stepHash :: (Int, [Int]) -> (Int, [Int])
+stepHash (xs, ys) = (foldl1 xor (take 16 ys), drop 16 ys)
+
+int2Hex :: Int -> [Char]
+int2Hex xs
+  | length ys == 2 = ys
+  | otherwise = '0':ys
+    where ys = showHex xs ""
+
+denseHash :: [Int] -> [Char]
+denseHash xs = mconcat $ fmap (int2Hex . fst) $ take 16 $ drop 1 $ iterate stepHash (0, xs)
+
+solve2 :: [Char]
+solve2 = denseHash $ sparseHash $ (ord <$> input) ++ [17, 31, 73, 47, 23]
+
 input = "120,93,0,90,5,80,129,74,1,165,204,255,254,2,50,113"
-- 
cgit v1.2.3