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    1 {-|
    2 Module:      Y2015.D13
    3 Description: Advent of Code Day 13 Solutions.
    4 License:     MIT
    5 Maintainer:  @tylerjl
    6 
    7 Solutions to the day 13 set of problems for <adventofcode.com>.
    8 -}
    9 
   10 module Y2015.D13 (solveSeating) where
   11 
   12 import           Data.List   (nub, permutations)
   13 import           Data.Map    (Map, findWithDefault, fromList, keys)
   14 
   15 type Guest       = String
   16 type Happiness   = Int
   17 type Edge        = (Guest, Guest)
   18 type Preferences = Map Edge Happiness
   19 
   20 -- |Find optimal seating happiness!
   21 solveSeating :: String -- ^ Input of seating happiness stats
   22              -> Int    -- ^ Optimal possible happiness
   23 solveSeating i = maximum $ map sum guestMoods
   24     where prefs        = toSeating i
   25           guests       = nub . uncurry (++) . unzip $ keys prefs
   26           pairs        = map (zip <*> tail . cycle) $ permutations guests
   27           arrangements = map rePair pairs
   28           guestMoods   = map (map (flip (findWithDefault 0) prefs)) arrangements
   29 
   30 rePair :: [(a, a)] -> [(a, a)]
   31 rePair []         = []
   32 rePair ((x,y):xs) = [(x,y),(y,x)] ++ rePair xs
   33 
   34 toSeating :: String -> Preferences
   35 toSeating = fromList . map (parseSeating . words . init) . lines
   36 
   37 parseSeating :: [String] -> (Edge, Happiness)
   38 parseSeating [a,_,s,h,_,_,_,_,_,_,b] = ((a, b), hap s)
   39     where change = read h
   40           hap "lose" = negate change
   41           hap _ = change
   42 parseSeating _ = (("", ""), 0)