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    1 {-|
    2 Module:      Y2015.D08
    3 Description: Advent of Code Day 08 Solutions.
    4 License:     MIT
    5 Maintainer:  @tylerjl
    6 
    7 Solutions to the day 08 set of problems for <adventofcode.com>.
    8 -}
    9 
   10 module Y2015.D08 (difference, encoded) where
   11 
   12 body :: [a] -> [a]
   13 body []  = []
   14 body [_] = []
   15 body xs  = tail $ init xs
   16 
   17 hexChars :: String
   18 hexChars = "0123456789abcdef"
   19 
   20 escape :: String -> String
   21 escape []                                   = []
   22 escape [x]                                  = [x]
   23 escape (v:w:x:y:zs) | [v,w] == "\\x" && hex = '.'  : escape zs
   24                     where hex = all (`elem` hexChars) [x,y]
   25 escape (x:y:zs)     | [x,y] == "\\\""       = '"'  : escape zs
   26                     | [x,y] == "\\\\"       = '\\' : escape zs
   27                     | otherwise             = x    : escape (y:zs)
   28 
   29 encode :: String -> String
   30 encode = (++) "\"" . (:) '"' . encode'
   31 
   32 encode' :: String -> String
   33 encode' []                 = []
   34 encode' (x:xs) | x == '"'  = '\\' : '"' : encode' xs
   35                | x == '\\' = "\\\\"    ++ encode' xs
   36                | otherwise = x          : encode' xs
   37 
   38 squish :: String -> String
   39 squish = filter (/= '\n')
   40 
   41 solve :: (Int -> Int -> Int) -> (String -> String) -> String -> Int
   42 solve g f s = g (original s) (new s)
   43     where original = length . squish
   44           new      = length . squish . unlines . map f . lines
   45 
   46 -- |Finds the length difference between escaped and unescaped string
   47 difference :: String -- ^ Input string with escapes
   48            -> Int    -- ^ Unescaped length difference
   49 difference = solve (-) (escape . body)
   50 
   51 -- |Same as 'encoded', but different
   52 encoded :: String -- ^ Input string with escapes
   53         -> Int    -- ^ Length difference to encoded string
   54 encoded = solve (flip (-)) encode