2015 Day 03 in Haskell

2015/day03/day03.hs

@@ -0,0 +1,24 @@
+import Aoc
+import Data.List
+
+parseFile :: [String] -> [Char]
+parseFile = single
+
+move :: (Int, Int) -> Char -> (Int, Int)
+move (x, y) 'v' = (x, y - 1)
+move (x, y) '^' = (x, y + 1)
+move (x, y) '<' = (x - 1, y)
+move (x, y) '>' = (x + 1, y)
+
+visited :: [Char] -> [(Int, Int)]
+visited = uncurry (:) . foldl (\(loc, locs) c -> (move loc c, loc:locs)) ((0, 0), [])
+
+part1 :: [Char] -> Int
+part1 = length . nub . visited
+
+part2 :: [Char] -> Int
+part2 = length . nub . uncurry (++) . both visited . split
+    where split cs = foldr (\(c, i) (evens, odds) -> if even i then (c:evens, odds) else (evens, c:odds)) ([], []) (zip cs [0..])
+
+main :: IO ()
+main = aocMain parseFile part1 part2

aoc.hs

@@ -18,4 +18,10 @@ pair :: [a] -> (a, a)
 pair as = let [a1, a2] = as in (a1, a2)
 
 triplet :: [a] -> (a, a, a)
-triplet as = let [a1, a2, a3] = as in (a1, a2, a3)
+triplet as = let [a1, a2, a3] = as in (a1, a2, a3)
+
+single :: [a] -> a
+single as = let [a] = as in a
+
+both :: (a -> b) -> (a, a) -> (b, b)
+both f (a, b) = (f a, f b)