Added solution for day 3

3/example.txt

@@ -0,0 +1,12 @@
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010

3/solution.hs

@@ -0,0 +1,55 @@
+import Data.Bits ( complement, Bits (shift, shiftR, rotate, complementBit), shiftL, (.|.) )
+import Data.List (transpose, isPrefixOf, inits, find, tails, sort)
+import Debug.Trace
+import Data.Maybe
+
+main :: IO ()
+main = readFile "3/input.txt" >>= print . solve . parse . lines
+
+parse :: [String] -> [String]
+parse = id
+
+solve :: [String] -> (Int,Int)
+solve input = (f input, g input)
+    where f = powerUse . transpose
+          g = lifeSupport
+
+powerUse :: [String] -> Int
+powerUse i = gamma i * epsilon i
+    where
+        gamma   = pack . rate (>=)
+        epsilon = pack . rate (<)
+
+rate :: (Int -> Int -> Bool) -> [String] -> [Int]
+rate op = foldr (\c -> (:) (
+        let ones   = count '1' c;
+            zeroes = count '0' c;
+        in if ones `op` zeroes
+            then 1
+            else 0
+    )) []
+    where
+        count x = length . filter (== x)
+
+lifeSupport :: [String] -> Int
+lifeSupport i = oxygen x * scrubber x
+    where
+        x = reverse i
+        oxygen   = rating 0 (>=)
+        scrubber = rating 0 (<)
+
+rating :: Int -> (Int -> Int -> Bool) -> [String] -> Int
+rating _ _ [result] = convert result
+rating n op list    = rating (n + 1) op (filter (\a -> (a !! n) == (f (transpose list) !! n)) list)
+    where 
+        f = map (head . show) . rate op
+
+pack :: [Int] -> Int
+pack = foldl f 0
+    where
+        f acc i = acc `shiftL` 1 .|. i
+
+unpack :: String -> [Int]
+unpack = map (\x -> if x == '0' then 0 else 1)
+
+convert = pack . unpack